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22george

Turbo cool down period

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How long do you guys let your engine cool down before turning it off? Down to what egt??I've been letting it cool down to 320-340 before I shut it off.Thanks

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That's a good number. I think most wait for 300. Really it depends on what you did beforehand. The oil gets hotter the more you load the engine (towing) so you want to give it a chance to cool down. As I think about it, I don't think egts are a very accurate indicator of when to shut down, I think an oil temp gauge in the oil outlet of the turbo would be a lot better. Just because the egt is cool doesn't mean the engine oil is cool (which is the reason you wait for the egts to go down, so the oil won't coke in the turbo). If you think about it, the coolant runs the same temp all the time, but under a load the higher egts are transfered to the oil because the pistons are getting hotter and are cooled by the oil. So when you get done towing, the oil is hot, the engine will get to 300* way quicker than the oil cools down from idling (pistons no longer heating it much). You have to give the cooling system some time to pull the heat out of the oil.Egt is a decent indication of load though, since the engine will have to cool a bit to stop heating the egts up. But if you notice, the egts go right back.up after shutdown do to heat soak, that is what you are trying to do while idling, get the heat out of the turbo via oil cooling. In short, if I drive 55 mph unloaded, I could care less what the Egt says. If i pull a trailer, I will watch egts and wait for 300 plus 2 minutes. If its a big load that sent coolant temps over 200 the whole time, then wait for 190 coolant, 300 Egt, plus 2 min.Just my theory of the day.

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Just riding around town or other short trips i let my egt cool to below 350*. if i am towing i will let it cool to below 300* and sometimes i dont shut it down. jsut depends on how hard i have been running it.I have wondered about the oil temp before like ISX mentions but at the time have no way to monitor it. i have 247k on her and the turbo is still in great shape as far as i can see.

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Just riding around town or other short trips i let my egt cool to below 350*. if i am towing i will let it cool to below 300* and sometimes i dont shut it down. jsut depends on how hard i have been running it. I have wondered about the oil temp before like ISX mentions but at the time have no way to monitor it. i have 247k on her and the turbo is still in great shape as far as i can see.

Yeah there is no way to monitor it really so we have to use EGT instead, though I might try and dig up a fancy sensor.

Oil temp typically follows the coolant temp fair close running empty... (Second hand info) So I tend to watch EGT's and Coolant Temp (Scan Gauge II) and try for below 350*F and below 193*F...

Running empty... Plus that still isn't exactly the thing. What I am getting at is that it's the heatsoak that does the coking "supposedly". My turbo didn't look too bad when I took it apart, but putting the new shaft in seemed to really make a difference. I'm thinking even a little coking has negative effects on performance. I am sure all of you have seen those pics of those glowing red turbos. Lets say the cooling system is big enough to handle that kind of combustion heat, so the coolant remains at 200F. The turbo on the other hand, sees all of the heat and gets very hot. I can floor it going up a hill and watch the EGT skyrocket over 1200F, yet I can top the hill and go downhill and watch the EGT go to 300F or less, yet pushing in the clutch you can watch it go back up to 400F, that is heat soak. It is an illusion because all the air the engine is pumping cools the EGT probe, even though the exhaust manifold and turbo remain very hot. Remember that the turbo in itself produces heat being something that spins several thousand RPM's. I don't think EGT's have anything to do with how hot the turbo is. Oh and the oil temp being the same thing...I want to see the temp on the oil outlet of the turbo.. Go 55mph for a while, until everything is nice and warmed up, then idle for 5 minutes and see what the oil temp is at that location. Now beat the crap out of it and see how long it takes to idle to get to the same temp and also note what your EGT says. I realize I am rocking the boat and I never thought this way until reading the title and it just kinda hit me. I think the oil cooler probably does a good job, but how long does it take to drain all the "coking heat" out of the turbo so the heat soaking doesn't coke it all. Thanks to whoever fixed my previous post. I typed it all with my cell phone at lunch :lol:

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I run an oil temp gauge. Generally, it takes about twice as long for the oil to get back to normal operating temperature, than the coolant. Even at 75 mph, it still takes about 2 x's as long. Most of the time my oil temp is about 185* at operating temp, after a pull, the oil temp went up to 224*, the coolant temp was at about 220*. It took about 2 minutes to have the coolant down to 190* and about 4 minutes to have the oil temp down to 190* also. This was at 75 mph. So it may take a bit longer if you are sitting idling to get the oil temp down. Posted Image Here is where I put the sensor for the oil temp. It is in the oil filter housing, next to the turbo line.

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When i come off the highway towing i usually just take it very easy in a lower gear all the way to the gas station. Just creeping along probably pissing everybody off, but it tends to help cool every thing off fairly well. by the time i get to the pump I am usually at no more than 350*. if i am just going to pump and run I just leave it running. if not i let cool to 300*, fill it up,and do my what ever it is I am going to do. then it is back on the road.

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I run an oil temp gauge. Generally, it takes about twice as long for the oil to get back to normal operating temperature, than the coolant. Even at 75 mph, it still takes about 2 x's as long. Most of the time my oil temp is about 185* at operating temp, after a pull, the oil temp went up to 224*, the coolant temp was at about 220*. It took about 2 minutes to have the coolant down to 190* and about 4 minutes to have the oil temp down to 190* also. This was at 75 mph. So it may take a bit longer if you are sitting idling to get the oil temp down. Posted Image Here is where I put the sensor for the oil temp. It is in the oil filter housing, next to the turbo line.

Ah HA! And that's the oil going to the turbo, so who knows what the oil from the turbo is doing. I'll get a gauge and figure this out.

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Ah HA! And that's the oil going to the turbo, so who knows what the oil from the turbo is doing. I'll get a gauge and figure this out.

OH LAWD! ISX is at it again. :lmao2: Fun stuff ISX. You ask the most interesting questions and expect valid answers with NUMBERS in them.

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this is one reason why i am headed to a water cooled turbo. it is the latent heat in the turbo housing and any heat that creeps from the head to the headers and then into the turbo that does the cooking. but then again i can usually shutdown at most places under 300* by the time i pull in.

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I would think that while you are idling and cooling down the oil flowing through the turbo would be cooling it also. Is 225 degrees oil temp a problem shutting down? My water temp has not gone above 190. Don't know, just throwing it out there wanting to see what everyone thinks.Thanks for the responses

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ISX, I'm following what you're saying but without trying to rock your boat, sorry but I dont agree, and here's why. First off the turbo isn't hot because its "spinning real fast" but in reality because the turbo is a compressor whereby the process of compressing air itself creates heat and also because the turbo impeller brunt's the direct heat of cylinder combustion. So for that reason, when the combustion temps are low, the turbo is no longer producing boost, and cooler air is flowing through it, then the turbo housing is cooling off. Heat soak can only take place when one object is hotter than another object but size of the subject objects also plays a part in how much heat soak takes place. Meaning that the cooler larger engine wont heat soak the smaller hotter turbo and vice versa. But hypothetically lets say if the engine was 400* and the turbo was 300* then definitely the hotter engine would increase the temp of the smaller turbo after shutdown.The lubricating oil passing through the turbo bearing housing is always safe as long as its continually flowing through. But because of the general design of the turbo bearing, the film of oil in the bearing bushing is measuring hundredths of a millimeter whereby allowing the turbo shaft to spin so freely. And because there is so little oil volume within that bearing surface, the oil is more susceptible to coking. You can use the engine oil temp in your cool down variable but oil temps should be no more than about 225* at the hottest anyways which means that the oil temp will have no effect on cool down time since the general temperature of the crankcase oil will always be less than the turbo. So what I'm getting at is there's no way to address the oils temp within the turbo after shutdown unless you allow enough engine idle time so the cooler EGT’s can reduce the turbo housing temp, you have a turbo timer to do this for you, or you have a way to continue pump oil through the turbo bearing via a separate electric oil pump.....or something of that nature. There are such devices too.I think what you’re trying to address is that idling after high load conditions means that the turbo housing could easily be hotter than one would think simply using the EGT’s to reference from. An example of that would be to place the engine under a good load like towing down the highway and then pull over. Idle for until the EGT’s drop to about 325*-350* and then shut down. But…..(if your thermocouple is mounted pre-turbo) then continue to watch the EGT’s with the engine off and you’ll see how the EGT’s will continue to rise around another 100* or so before they level off. The lower the load on the engine during running, the less this will happen. Thus the reason why Cummins states their specific idle cool down times as per certain driving conditions. Cummins doesn’t care about the oil temp coming out of the turbo because, as I stated, the real concern is the temperature of the turbo housing, not the oil, because the oil coking takes place when the turbo housing is hot enough that the oil left within the bearing surface cannot escape before the turbo housing temperature can drop to where a specific oil isn't subject to coking. That temp is roughly 300*-350* but you can add about 100* with synthetics since "true" synthetics will coke at higher temps then conventional oils. Not sure why I’m going on and on about this either but my point is that the only thing we can or should care about is that the EGT’s are low and are going to stay low enough after shutdown that there is no chance of oil coking. That’s all…..:)

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ISX, I'm following what you're saying but without trying to rock your boat, sorry but I dont agree, and here's why. First off the turbo isn't hot because its "spinning real fast" but in reality because the turbo is a compressor whereby the process of compressing air itself creates heat and also because the turbo impeller brunt's the direct heat of cylinder combustion. So for that reason, when the combustion temps are low, the turbo is no longer producing boost, and cooler air is flowing through it, then the turbo housing is cooling off. Heat soak can only take place when one object is hotter than another object but size of the subject objects also plays a part in how much heat soak takes place. Meaning that the cooler larger engine wont heat soak the smaller hotter turbo and vice versa. But hypothetically lets say if the engine was 400* and the turbo was 300* then definitely the hotter engine would increase the temp of the smaller turbo after shutdown. The lubricating oil passing through the turbo bearing housing is always safe as long as its continually flowing through. But because of the general design of the turbo bearing, the film of oil in the bearing bushing is measuring hundredths of a millimeter whereby allowing the turbo shaft to spin so freely. And because there is so little oil volume within that bearing surface, the oil is more susceptible to coking. You can use the engine oil temp in your cool down variable but oil temps should be no more than about 225* at the hottest anyways which means that the oil temp will have no effect on cool down time since the general temperature of the crankcase oil will always be less than the turbo. So what I'm getting at is there's no way to address the oils temp within the turbo after shutdown unless you allow enough engine idle time so the cooler EGT’s can reduce the turbo housing temp, you have a turbo timer to do this for you, or you have a way to continue pump oil through the turbo bearing via a separate electric oil pump.....or something of that nature. There are such devices too. I think what you’re trying to address is that idling after high load conditions means that the turbo housing could easily be hotter than one would think simply using the EGT’s to reference from. An example of that would be to place the engine under a good load like towing down the highway and then pull over. Idle for until the EGT’s drop to about 325*-350* and then shut down. But…..(if your thermocouple is mounted pre-turbo) then continue to watch the EGT’s with the engine off and you’ll see how the EGT’s will continue to rise around another 100* or so before they level off. The lower the load on the engine during running, the less this will happen. Thus the reason why Cummins states their specific idle cool down times as per certain driving conditions. Cummins doesn’t care about the oil temp coming out of the turbo because, as I stated, the real concern is the temperature of the turbo housing, not the oil, because the oil coking takes place when the turbo housing is hot enough that the oil left within the bearing surface cannot escape before the turbo housing temperature can drop to where a specific oil isn't subject to coking. That temp is roughly 300*-350* but you can add about 100* with synthetics since "true" synthetics will coke at higher temps then conventional oils. Not sure why I’m going on and on about this either but my point is that the only thing we can or should care about is that the EGT’s are low and are going to stay low enough after shutdown that there is no chance of oil coking. That’s all…..:)

It was just a theory I had. I believe what you are saying but I like numbers. I will go with what you say until I can prove otherwise :lol: I need more gauges apparently. It is people like you that make me learn more so it's good that you stepped up and debated my theory.

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It was just a theory I had. I believe what you are saying but I like numbers. I will go with what you say until I can prove otherwise :lol: I need more gauges apparently. It is people like you that make me learn more so it's good that you stepped up and debated my theory.

Thank you ISX. I appreciate your compliments and I dont claim to be "right" or any smarter than anyone else either. I kinda think the whole oiled turbo bearing concept is a little archaic but it does work and work well. I actually thought that air cushioned turbo bearings were on their way, but then again I haven't been paying to much attention. Its just that the everyday person usually doesn't have the required patience to make sure they allow enough cool down time for their turbo vehicle. If you ever feel like checking you'll find that most mechanical issues with turbo charged gasoline engines are turbo failure related. Thats because gas engines run so much hotter than diesel and unless the car is special in someway, like very expensive or very rare, then the consumer doesn't care and/or isn't smart enough to know how to properly treat their turbo engine. The same rule of thumb applies to limited slip differentials. Everyone complains that their LS sucks but they fail to realize that their one tire burn out, constant u-turning under power, and never changing the lube has or is destroying the LS clutches. In short, manufactures go through a lot of effort to make their product as simple and easy so people dont have to worry about what to do otherwise most people wont want it. Thus the reason Banks does so well. :)

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Thank you ISX. I appreciate your compliments and I dont claim to be "right" or any smarter than anyone else either. I kinda think the whole oiled turbo bearing concept is a little archaic but it does work and work well. I actually thought that air cushioned turbo bearings were on their way, but then again I haven't been paying to much attention. Its just that the everyday person usually doesn't have the required patience to make sure they allow enough cool down time for their turbo vehicle. If you ever feel like checking you'll find that most mechanical issues with turbo charged gasoline engines are turbo failure related. Thats because gas engines run so much hotter than diesel and unless the car is special in someway, like very expensive or very rare, then the consumer doesn't care and/or isn't smart enough to know how to properly treat their turbo engine. The same rule of thumb applies to limited slip differentials. Everyone complains that their LS sucks but they fail to realize that their one tire burn out, constant u-turning under power, and never changing the lube has or is destroying the LS clutches. In short, manufactures go through a lot of effort to make their product as simple and easy so people dont have to worry about what to do otherwise most people wont want it. Thus the reason Banks does so well. :)

This is true. It's just hard knowing when is the "right" time to shut down. I mean who was the person who originally decided 300 was the shutdown point? I am not saying it isn't the right temp I just like to see where this stuff was derived. Plus it is just interesting lol.

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Thats what drew me to Banks 6 years ago. One package with every thing I thought I needed. Fuel pressure was not issue with them then. Might have done it differantly knowing what i know now, but who knows. It is still serving me well though and I am happy with it.

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This is true. It's just hard knowing when is the "right" time to shut down. I mean who was the person who originally decided 300 was the shutdown point? I am not saying it isn't the right temp I just like to see where this stuff was derived. Plus it is just interesting lol.

I have always been under the impression that conventional oils will coke under a "constant" temperature of around *400 whereby some synthetics can sustain around 100* more. So if this is actually accurate information, maybe Cummins listed the cool down time and temp considering and how long it would take the turbo housing to reach a safe temp. Dont know but I do know when I used to cook that everyday cooking oils/shortenings can self ignite at around 475*-500*.

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i think one thing that is missed in this discussion is the cumulative effects of high turbo temp shutdown causing the coking.The time it takes for the oil to actually BBQ in the turbo probably is around the time that the turbo actually starts getting below the coking temp. But that small overlapping timeframe over and over again from heavy towing/no cooldown could be causing the cumulative buildup of coked oil in the bearing race.For us daily drivers, we shut down with minimal cooldown but yet there are no problems. Those that have had turbo bearing failure probably got the turbo real hot, and shutdown with non-sufficient cooldown times thus causing the buildup over time leading to failure.thoughts?

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I'll show you guys something interesting. Pics of my turbo after taking it apart. Probably 300k miles of buildup.

Here is the shaft I pulled out.

Posted Image

and the brand new one I got.

Posted Image

I polished the other one up and that back half took forever. It is very close to the exhaust gasses itself being that that is the turbine and it shows that the oil gets hot.

Posted Image

Posted Image

Thing is, putting that new shaft in helped turbo spoolup tremendously. I should take it apart again and see what it looks like since it probably has 10k miles on it now.

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Great photos ISX. Tells the true tale about whats going on.And I think that CUMMINSDIESELPWR is right on the money regarding cumulative hot shutdowns. This would be something that would happen over a period of time for the average vehicle. Matter of fact, somewhere I was reading that another common problem with turbo engines is people who dont allow enough start up idle time for the oil to properly circulate through the engine and turbo before reving the engine or taking off. Until the oil is fluid, the turbo bearings are basically running dry but the shaft will still spin in relation to the engines RPM's. Bad for the bushing and shaft.

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When I am pulling my fifth wheel I planed my stops so that way I start slowing down so it will cool down on it Owen. I will let it idle for about 2 mints then shut down.

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