[RangerGress]

The max temp per vm motori of 284 is sump temps aka in the oil pan. The derate temp of 268 F is post oil cooler which is whats measured. When coolant comes back from the radiator it’s typically around 30-50 degrees lower than whats displayed on most engines the displayed temp is at the return for the water pump which is hottest.

Re. oil temp. Understood, thx.

We'll probably never agree re. our oil cooler, but I do have the Ram engineer on my side on that.

30-50deg of temp drop sounds high. I've taken an IR gun to radiator inlet/outlet hoses and AL bits many times and the temp drop across the radiator is much less than that. Water is moving pretty fast thru the coolant system. There wouldn't be enough time in the radiator to drop so much temp.

I went looking for some numbers to remind myself how pressure and anti-freeze impacts boiling temps. The bottom line is that we have become accustomed to coolant temps pretty darn close to the boiling point of our coolant.

The boiling point of water goes up only slowly with pressure, and once the coolant is out of the engine, the system isn't under much pressure. Sure, anti-freeze has an anti-boil but the standard 50/50 mix only gives you about 15deg of protection.

The chart below shows how pressure increases the boiling point of antifreeze. Note 236deg for 50% solution at 4psi. There's got to be parts of the coolant system that are as low as 4psi because the pump is sucking and the pressure at the radiator inlet will be only barely higher.

The chart below indicates that the boiling point of antifreeze at 4psi is 236deg and pressure in the hose between the engine and radiator inlet is not going to be much more than that. As coolant temp increases, so does pressure due to microboiling. That's good in the sense that increased pressure helps keeps coolant flashing at bay, but the increased pressure also stresses gaskets and hoses leading to premature failure. So when your EVIC says your coolant temp is >225deg, consider how close you are to bad things.

Sure, it's not a crisis because engines aren't blowing up every day due to coolant overheats, but it does seem to be a thin margin of error. We know that coolant related things fail on these trucks, and here we are talking about the coolant system putting unusual stress on bits.

Situation at high altitudes is worse. A mile of elevation and you lose about 25% of air pressure. That would drop the boil point by about 8deg.

 

[Brokedownbutgood]

There well be no where in the cooling system thats under vacuum at operating temps the cap pressure for the expansion tank is 21 psi I suspected based off lots of testing on other engines block pressure is around 50-60 psi in the upper rpm range. Might be as low as 20 psi other wise. Either way coolant boiling is only a concern if the system is low or has a leak. Personally I want coolant temps between 180-210 F and oil temps between 210-240 F. But that would require a major redesign to the cooling system to get there. Cooling systems pressurize as they heat the entire system is sealed and water pumps are not positive displacement.

 

[RangerGress]

There well be no where in the cooling system thats under vacuum at operating temps the cap pressure for the expansion tank is 21 psi I suspected based off lots of testing on other engines block pressure is around 50-60 psi in the upper rpm range. Might be as low as 20 psi other wise. Either way coolant boiling is only a concern if the system is low or has a leak. Personally I want coolant temps between 180-210 F and oil temps between 210-240 F. But that would require a major redesign to the cooling system to get there. Cooling systems pressurize as they heat the entire system is sealed and water pumps are not positive displacement.

I think that in order for the water pump to add significant pressure to the coolant, call it 10psi, there would have to be flow restriction in the system and there isn't. The coolant system is designed to flow freely. Sure, the holes in the headgasket are kinda small, but there's a bunch of them and it's not like the water pump is designed to move 100gal/min. Can't be the tstat providing the flow restriction because when the water is really hot it's fully open.

I can probably test the system pressure. Just takes putting a gauge on.

As a data point, the expansion tank reservoir for the BMW race car is also 21psi. I've done a lot of testing on that coolant system. The pressure in the block doesn't turn off the 7psi coolant pressure warning light until the coolant gets good and hot. That means that the waterpump, churning cold water against the closed thermostat, can't get to 7psi. That tells us something about water pump design. Sure, it's not the same water pump, but when the design imperatives are the same the designs tend to be pretty similar.

I found some old test data. The coolant pressure in the race car varies from 2-12psi depending on temp, rpm, and location tested.

Hard to imagine how our coolant hoses would handle 50-60psi. When I was messing with them the other day, I didn't notice any reinforcing like you'd see with fuel injection hose.

 

[RangerGress]

There well be no where in the cooling system thats under vacuum at operating temps the cap pressure for the expansion tank is 21 psi I suspected based off lots of testing on other engines block pressure is around 50-60 psi in the upper rpm range. Might be as low as 20 psi other wise. Either way coolant boiling is only a concern if the system is low or has a leak. Personally I want coolant temps between 180-210 F and oil temps between 210-240 F. But that would require a major redesign to the cooling system to get there. Cooling systems pressurize as they heat the entire system is sealed and water pumps are not positive displacement.

Ok, I tested pressure at the reservoir. 0 psi up to 205deg. Pressure then jumped to 4psi at 210deg, and stayed there until 212 which is when I shut down the truck. Certainly the pressure will go up a bit more as the coolant gets extremely hot, but there's a limit to how hard I want to run the truck sitting at the curb. No reason to imagine that the coolant pressure goes up sharply.

I was running the truck at 2500rpm the whole time with the pressure gauge readable from inside the truck. If rpm had an effect on reservoir pressure, it was too slight for me to notice. Like I said, the pump isn't the primary driver of coolant pressure. Microboiling is. Certainly the pressure immed after the pump, at 2500rpm, is higher than the pressure at the reservior tho.

Note that these #'s are essentially the same as the race car's that I discussed.Not surprising, pretty much the same problem--get heat out of the engine, pretty much the same solution.

I also noticed that the radiator return got warm at 195, and was clearly passing plenty of hot coolant by 197. So much for the tstat not opening until 208deg.

All temps at the EVIC.

Video goodness.

 

[howie12]

I will point out that there seems to be no evidence there is cavitation at the water pump. For those that haven't heard it is is very loud and sounds like marbles are flowing through the pump. For those that haven't seen a centrifugal pump apart that has been subject to cavitation you will see large rounded erosion depressions in an iron or steel impeller. I feel confident at whatever temps our trucks are running at or might achieve the design does not permit cavitation at the water pump. If it occured the damage would be quick and obvious. If you want to see some typical pics of an impeller that has been cavitating you can go to centrifugal pump cavitation pictures - Google Search

 

[RangerGress]

I will point out that there seems to be no evidence there is cavitation at the water pump. For those that haven't heard it is is very loud and sounds like marbles are flowing through the pump. For those that haven't seen a centrifugal pump apart that has been subject to cavitation you will see large rounded erosion depressions in an iron or steel impeller. I feel confident at whatever temps our trucks are running at or might achieve the design does not permit cavitation at the water pump. If it occurred the damage would be quick and obvious. If you want to see some typical pics of an impeller that has been cavitating you can go to centrifugal pump cavitation pictures - Google Search

I wouldn't expect cavitation to be an issue. It's a pretty controlled environment and preventing cavitation, I think, is mostly just blade design since rpms and pressure before/after are all known. The environment is so predictable that cavitation occurring would be a really big design screwup.

 

[howie12]

I think that in order for the water pump to add significant pressure to the coolant, call it 10psi, there would have to be flow restriction in the system and there isn't. The coolant system is designed to flow freely. Sure, the holes in the headgasket are kinda small, but there's a bunch of them and it's not like the water pump is designed to move 100gal/min. Can't be the tstat providing the flow restriction because when the water is really hot it's fully open.

I can probably test the system pressure. Just takes putting a gauge on.

As a data point, the expansion tank reservoir for the BMW race car is also 21psi. I've done a lot of testing on that coolant system. The pressure in the block doesn't turn off the 7psi coolant pressure warning light until the coolant gets good and hot. That means that the waterpump, churning cold water against the closed thermostat, can't get to 7psi. That tells us something about water pump design. Sure, it's not the same water pump, but when the design imperatives are the same the designs tend to be pretty similar.

I found some old test data. The coolant pressure in the race car varies from 2-12psi depending on temp, rpm, and location tested.

Hard to imagine how our coolant hoses would handle 50-60psi. When I was messing with them the other day, I didn't notice any reinforcing like you'd see with fuel injection hose.

While I have not seen an example of the thermostat in our trucks every thermostat I have seen (more than hundreds but less than thousands) provides a significant restriction compared to no thermostat. In the olden days most every radiator flush would tell you to remove the thermostat before using the flush. The flow increase is obvious by just looking in the radiator with the thermostat in vs out. I do not agree technically that the comment that the thermostat provides no restriction because it is fully open is correct. From my experience the thermostat provides significant restriction when it is fully open. Look carefully at one and it should be clear that the flow path when fully open is quite restrictive compared to an open pipe. I feel certain when you think about this you will agree.

 

[howie12]

I wouldn't expect cavitation to be an issue. It's a pretty controlled environment and preventing cavitation, I think, is mostly just blade design since rpms and pressure before/after are all known. The environment is so predictable that cavitation occurring would be a really big design screwup.

What I didn't clearly state and should have is if the fluid in the engine was anywhere near boiling there would be cavitation at the pump(the lowest pressure point of the coolant in the engine) and since we have no evidence of that the pump suction is well above boiling in all circumstances since if it wasn't the impeller would be quickly destroyed by cavitation.

 

[howie12]

Re. stop comparing. The design of the cooling systems, from block and head water jacket to radiator is pretty close to identical.

Re. diesel engines run hotter. And it's a water cooled turbo. So maybe it should have gotten a bigger radiator then the Pentastar.

Re. max oil temp is 284deg. In the other thread you said the oil derate temp is 269deg, so I'm confused. High temp deration, oil or coolant? Is derate temp different than max temp?

Re. can't cool fluid with only a 5-10deg delta. I'd have to know more about the use case. If there seems to be a disconnect between the physics and what we're observing, it's always because we're missing something. The pic below shows the heat xfer equation for conduction and a quick glance shows that heat xfer is proportional to temp delta and surface area. So if you've got a small temp delta, you have to make up for it with huge surface area. There is just no getting around the fact that as delta T goes down, surface area has to go up. A heat exchange system wouldn't get designed with a small temp delta unless there was no other choice because making something big is expensive. In heat xfer, one always gets the two temps as far different as you can because that allows for a small heat exchanger.


View attachment 88877

Perhaps this calculation is coming from a typical wooden house building application with air on both sides. As I wrote in the past my one course of Thermo was a gazillion years ago and not up to your 3 courses. That said I would posit that the same exchanger with water on one side and air on the other would transfer a different amount of heat if there were water on both sides even if the delta t is the same. Seems to me the properties of the fluid must influence the amount of heat transferred. bticbw

 

[RangerGress]

Re. thermostat is a restriction. Agreed, it is a restriction to some extent. As a result of that restriction, the coolant pressure in the block is higher than in the radiator and reservoir. But the question becomes "how much of a restriction?" And I would argue "it does its job by being a restriction, but at full open its job is to be not enough restriction to matter. The coolant system has to move a fair amount of water in order to do it's job. So engineering a tstat that presented a problematic restriction at full open would be silly."

It's not a matter of using the restriction to keep the block and heads pressurized in order to prevent the coolant from flashing. The problem location for flashing is the hose to the radiator. The pressure there is low but the temp is high.

Re. cavitation. Hmm. There's no indication that the pressure at the intake of the pump is negative, at least not when the coolant is hot. Might be a bit negative when the thermostat is closed. Also, the intake to the pump is probably from the radiator return, the lowest temp point of the system. So that combo of relatively cool water and the fact that the system is pressurized by microboiling seems to be sum to a pump that doesn't cavitate at the intake. <shrugs shoulders>

Re. coolant being a better heat xfer fluid then air. All else being equal, sure. But we're not comparing fluids of the same temp, nor heat exchanges with the same surface area. We're comparing a real oil cooler with big surface area due to a zillion little fins to a little box not much bigger to a deck of playing cards, and ambient air temp vs. coolant temp at ~220deg.

 

[RangerGress]

I talked to a RAM engineer.

I remembered this afternoon that one of my racing buddies, that I've not seen in a while, is a RAM engineer, or at least used to be one. He works for Ford now on F-150 towing engineering. We talked over these Ram issues tonight. You guys will like some of his responses, others not.

He said:
1. I'm a little too obsessed with reduced coolant temps. He says that 225deg really isn't a problem.

2. The oil/cooler heat exchanger is not an oil cooler. What most of you have been calling an oil cooler is most certainly not. It's mission is to quickly warm up oil in frigid environments. That said, if oil temps do get much higher than the coolant temp, the oil/coolant heat exchanger will allow the coolant to moderate the temp of the oil a little bit.

3. Oil doesn't cool the engine. Coolant cools the engine. Cooling oil will have some effect on keeping the engine cooler, just not much.

4. It doesn't do oil any harm to get hot, call it 275deg. So obsessing over cooling it doesn't necessarily make sense, unless there's another reason like derating. So if derating is a problem and you know for certain that it's being caused by hot oil, cool your oil. Otherwise don't bother. If your oil is spending a lot of time hot, maybe change it a bit more often.

5. Radiator fans in trucks are more useful then I was giving them credit for. If it was just a radiator w/o a bunch of crap in front of it, the utility of a fan would drop away at about 30mph. But there's so much crap in front of a radiator these days, that a well shrouded fan right behind the radiator can be useful at higher speeds. It's temperature controlled so comes on when it needs to. Pretty much no matter the truck's speed, cooling is improved when the fan comes on.

There was more, but it's time for another beer.

 

[Brokedownbutgood]

Well since I clearly am not an engineer but have lots of experience testing and working on them I decided to test my old thermostat, changed it when I did my water pump. It barely started to open at 198.8 F but didn’t actually fully unseat tell around 206 F. On the other side it didn’t seal back up tell around 195 F. Also keeping oil temps in check absolutely does cool the bottom end there is zero coolant down there if your piston cooling nozzles start to plug it well crack pistons from a lack of cooling, assuming the rod doesnt fail first.

 

[RangerGress]

Well since I clearly am not an engineer but have lots of experience testing and working on them I decided to test my old thermostat, changed it when I did my water pump. It barely started to open at 198.8 F but didn’t actually fully unseat tell around 206 F. On the other side it didn’t seal back up tell around 195 F. Also keeping oil temps in check absolutely does cool the bottom end there is zero coolant down there if your piston cooling nozzles start to plug it well crack pistons from a lack of cooling, assuming the rod doesnt fail first.

That thermostat behavior is pretty close to what I observed. Did tstat seem to fully open before water boiled? Good job doing some testing. Not enough of that in the world.

My #'s are temp from the EVIC, which is not going to be exactly the same as temp at the tstat's bimettalic device.

The oil cooling issue is one of prob 260deg vs. 230deg. You're talking re. extremes. Not going to throw a rod bearing because oil spend some hours at 260deg.

 

[Bounty Hunter]

I talked to a RAM engineer.

He said:
1. I'm a little too obsessed with reduced coolant temps. He says that 225deg really isn't a problem.

This we knew.

2. The oil/cooler heat exchanger is not an oil cooler. What most of you have been calling an oil cooler is most certainly not. It's mission is to quickly warm up oil in frigid environments.

Yes, we knew this too. Let's put it to bed, shall we?

3. Oil doesn't cool the engine. Coolant cools the engine. Cooling oil will have some effect on keeping the engine cooler, just not much.

Doesn't explain the piston cooling nozzles the engineers designed to spray oil onto the bottom of the pistons.

4. It doesn't do oil any harm to get hot, call it 275deg. So obsessing over cooling it doesn't necessarily make sense, unless there's another reason like derating. So if derating is a problem and you know for certain that it's being caused by hot oil, cool your oil. Otherwise don't bother. If your oil is spending a lot of time hot, maybe change it a bit more often.

5. Radiator fans in trucks are more useful then I was giving them credit for. If it was just a radiator w/o a bunch of crap in front of it, the utility of a fan would drop away at about 30mph. But there's so much crap in front of a radiator these days, that a well shrouded fan right behind the radiator can be useful at higher speeds. It's temperature controlled so comes on when it needs to. Pretty much no matter the truck's speed, cooling is improved when the fan comes on.

I've mentioned it before, but cooling my oil in an external oil cooler has subsequently reduced my coolant temps. I see large drops in oil temps based on air flow. You can keep your theories as all they've done is totally exhaust me by reading them.

Maybe you should consider removing your AGS as they often times close at highway speeds for improved aerodynamics. Doesn't do much for airflow across your coolant stack and your crazy high coolant temps lol.

 

[Brokedownbutgood]

That thermostat behavior is pretty close to what I observed. Did tstat seem to fully open before water boiled? Good job doing some testing. Not enough of that in the world.

My #'s are temp from the EVIC, which is not going to be exactly the same as temp at the tstat's bimettalic device.

The oil cooling issue is one of prob 260deg vs. 230deg. You're talking re. extremes. Not going to throw a rod bearing because oil spend some hours at 260deg.

The thermostat wasn't even close to fully open even at 210 F just barely unseated. In order to make it fully open I would have to use coolant instead of water so I could see it before it boils. But it does seem an engineer missed the mark on the opening point for the thermostat since there even stamped 98 which is 208 F.

 

[VernDiesel]

The former Ram engineer has confirmed what the consensus of forum has been since 2015.

4. "So if derating is a problem and you know for certain that it's being caused by hot oil, cool your oil."

Bounty and others did just that. Myself and most being cost adverse chose to simply mitigate it with throttle management. Thought this has been shown and discussed ad nauseum since 2015 and generally understood by the forum since then. Its in fact why GDE & other companies have built tested and a few even sold kits for this. Such as the one Bounty has. Ram likely used the 10.5 quart oil capacity to help mitigate the oil temp derate problem. As previously mentioned the new 3.0 having relocating the intercooler has bumped towing capacity by 3k while keeping the same cooling capacity and now only uses I believe 7 quarts of oil.


5. "Radiator fans in trucks are more useful then I was giving them credit for. If it was just a radiator w/o a bunch of crap in front of it, the utility of a fan would drop away at about 30mph. But there's so much crap in front of a radiator these days, that a well shrouded fan right behind the radiator can be useful at higher speeds. It's temperature controlled so comes on when it needs to. Pretty much no matter the truck's speed, cooling is improved when the fan comes on."

Conversely by relocating the heat soaked intercooler from in front of the radiator as I and others have suggested and as Ram has done in the gen 5 truck you get more cool fresh air to avert heat soak and allow for heat transfer. You always seemed to dismiss and ignore the idea. But it seems according to the results, Ram, and your Ram engineer it was not a foolish idea. Your larger radiator should help mitigate the derate and temps and keep the oil a little cooler a little longer as well as the water temps. Maybe I'll be wrong and it will show a great improvement. Certainly I'm no engineer as previously said i've just seen it work before in my 87 Buick Grand National and then in the Ford 3.5 & 2.7 Ecoboost.

 

[RangerGress]

At Bounty Hunter
Re. coolant temp not a problem. If one defines "problem" as engines blowing up, than yes we knew that. But my definition of the problem as it irritating me that the engine was getting well outside of the thermostat's management range--the optimal range for the engine to operate. If you don't like something, it's a problem. I'm the same way.

Re. the oil/water heat exchanger not being an oil cooler and "yes we knew that." Oh no. Folks here have been calling the oil warmer an oil cooler since the beginning. So "lets move on" indicates that you will no longer call it an oil cooler and you will correct others that do? You're well respected here, helping to make that clear would be a good thing for the community.

Re. Doesn't explain the piston cooling nozzles the engineers designed to spray oil onto the bottom of the pistons. What's to explain? The design reduces peak piston temps. That's not the same as cooling the engine. The little cyclical oil spritz could be pulling 10btu from the pistons while the radiator pulls 10000btu from the engine and turbo. It's just a little once per rev spritz, how much heat energy do you really expect it to remove?

Re. cooling oil reduced both oil temps and coolant temps. Of course it reduced oil temps. It should not have reduced coolant temps noticeably tho, the physics of that doesn't work. Whenever the physics of something doesn't work, it means that there's another fact at play. Recall that the Ram engineer supported me in this--that cooling the oil does not cool the engine. The oil does not move enough heat energy to make much of a dent in the cooling needs of the engine.

Re. removing my AGS. Agreed, that's a reasonable idea.

At Brokedownbutgood
Re. thermostat opens at 208deg. That's temp at the tstat. What we've been talking about is temp at the EVIC display. They sense coolant temp in different locations and in different ways. The EVIC clearly shows that a person can drive around town with their coolant temp at 195-199deg. So using the measuring stick of EVIC temp, the tstat is open. Otherwise we'd have to come up with a theory how a person can drive all day with no coolant circulating.

Recall the post about ALLDATA saying that the tstat management range is 208-225. Converting that to temp (208-195=13deg delta) at the EVIC means that the tstat is full open, and therefore no longer managing engine temp, at 212deg at the EVIC. Do you accept that 225deg at the EVIC is 13deg outside of the tstat's management range? Do you accept that the tstat's management range was selected because that's the optimum temp for the engine to run at?

Related, the RAM engineer also confirmed that tstat weep holes are an aid for getting air out of the coolant system, not for circulating coolant.

At VernDiesel
Sure, derating due to oil temps is bad. But there seemed to be a consensus opinion seemed to be that high oil temps, say 260deg, were themselves inherently bad. The only problem with high oil temps is the derate. So if someone doesn't get hit by the derate, or avoids it with their gas pedal, then high oil temp isn't a problem. Yet, I bet there's all sorts of enthusiastic posts here re. oil coolers, and I bet most of those folks have never experienced oil temp derate. They're enthusiastic about the idea because folks here have convinced them that 260deg is inherently bad.

I tried to explain that it's high coolant temps that are fundamentally bad because they stress gaskets. Just because the gaskets survive doesn't change the fact that the high temps are hard on them. Our block doesn't expand much with heat, but all the AL bits fastened to it expand quite a bit. It's gaskets that make up the difference.

I'm not beating on folks for wanting to cool oil in order to avoid oil temp derate--it's a perfectly logical effort. I'm beating on folks for imagining that 260deg oil is worse than 230deg coolant, for imagining that cooling oil cools the engine, and for calling our oil warmer an oil cooler.

Re. I was wrong about the effectiveness of the cooling fan and the impact of the location of the intercooler. Agreed. And I'm perfectly happy to be wrong. Every time I get corrected, I better understand the issue under discussion. I want to be correct, so if you correct me, you do me a service. An attitude that seems kinda rare in the world.

 

[Brokedownbutgood]

Piston cooling nozzles are not “a little once per rev spritz” there open tubes that get feed from a common galley spraying a constant oil stream at the bottom of the pistons. They do in fact pull a lot of heat out of the pistons and rods. Ive seen them get slightly bent or blocked and do major engine damage.

 

[MAS]

Anyone know what happens to the viscosity of the oil at 260+ degrees? According to the manufacturers 270+ degrees will not harm the oil itself, but does it put it outside of a good viscosity range for the engine?

 

[RangerGress]

Piston cooling nozzles are not “a little once per rev spritz” there open tubes that get feed from a common galley spraying a constant oil stream at the bottom of the pistons. They do in fact pull a lot of heat out of the pistons and rods. Ive seen them get slightly bent or blocked and do major engine damage.

I looked into the oil spray harder. You're probably right re. them being a continuous spray. And I accept that the lack of them can result in piston failure. But that doesn't mean that they pull out a lot of heat from the engine. Since we have no oil cooler, it's not possible that oil spray pulls a lot of heat from the engine. There'd be no way to dump the heat. They just pull enough heat energy to keep the pistons happy.

Recall that the inside of the engine block is a crazy whirling hurricane of air and oil. So in the absence of oil sprayers, the cylinder walls and the underside of the pistons would still get wetted by oil. The oil sprayers just add a bit more oil, and ensure that it gets deep into the piston under-side.

Cooling rods isn't an issue. Can't have rod bearings cook, but they have their own source of oil to keep them cool. The rod itself doesn't need to be cooled. It's moving incredibly fast thru the engine's internal hurricane of air and oil. That's so much contact with air and oil that the oil spray won't add anything.