Turbo temp after shutdown

[JOblenes]

I have been a long time reader, but this is my first post. Definitely one of the most useful websites I visit. I noticed something the other day when shutting down my truck and was wondering if others have experienced the same thing. I just got back from a short drive and was letting the turbo cool off, I usually try and have the EGT drop to 350F or below. There was something interesting on the radio that I wanted to finish listening to so I turned the truck off and rotated the key back in the accessory position which in addition to providing power to the radio also provided power to the EGT gauge. I sat there and watched it, and over the next two to three minutes it climbed back up to 450-475F (I am guessing just heat transfer through conduction up from the base of the probe). I have done this a few more times since and it is amazing how hot it can get again (sometimes over 500F) even after a fairly long cool down. Any one else notice this? I have my probe mounted pre-turbo just above the flange. Seems like there is still a lot of residual heat even after the cooldown process. Does anyone know the "coking" temperature typical motor oils? how about synthetics (eg. royal purple)?

 

[RAMINSPEED]

After I let mine cool off to 235 and shut it down and hit the accessory position on the key it will climb some 15 to 20 degrees. If you have an automatic transmission you need to let it idle in either D or N with the AC off or it will never cool down to its potential. My probe is where yours is and I have the digital BD X-Monitor. I think i'll try my inferred temp gage on the manifold next time to see the discrepancy with my BD gage.

 

[WCPoe]

I also have found that with the A/C on the temps don't want to come down. So as I pull in I push the A/C button off but leave the fan blower running so I stay cool while I let the turbo cool down.

 

[nickleinonen]

After I let mine cool off to 235 and shut it down

i'd need to idle mine for like 10 min to get to that point... i'll watch until the gauge touches 300° and then shut down... i have hopped back in just a few minutes later and watched the gauge and it was sitting close to 350° so that seems to be fine for me

 

[rbattelle]

I've taken some data and found that heat transfer from the engine to the atmosphere and conduction across the engine equalize the entire engine temperature to around 140 degrees over a period of about 1 hour (I have hard data to show this if anyone wants it).



I'm surprised your probe is reading as high as 500 degrees after the engine is shut down. I do expect it to soak up some heat from the engine (as you mention), but Nick's experience seems much closer to "normal" to me. Maybe it's a gauge problem?



My probe is post-turbo and doesn't indicate any temperature rise at all after shutdown.



-Ryan

 

[p-Bar]

Jonathan,

I read your situation and did some checking on mine, here's what I came up with, after driving for awhile with air temp 85 F water temp 200 I would let it idle down like you did to 350 degrees then shut down the engine and put key on acc watched the egt it never went up but after 5 min it did start going down . I did this a couple of times and came out with the same results. Is your thermocouple pushed in the exhaust man. far enough?? I am pre turbo. Hope this helps



Don

 

[KLockliear]

It's called heat soak and it's normal.



I normally tell customers that have a pyro to let the EGT's drop until they stabilize. Sometimes thats a few seconds, sometimes longer.

 

[JOblenes]

Thanks everybody for the input. Seems like this is not typical behaviour. I don't think there is anything wrong with the gauge but now I'm going to have to look into it. I have a handheld thermocouple conditioner (I work in a research facility) that I may have to hook up and get some readings with a proper cold junction.



Ryan, did you ever measure the temperature of the turbo housing/exhaust manifold itself?



Thanks,

 

[lmills]

Mine does the same thing once in a while. Usually after a long ride or hard ride. I let it cool down to 350 then shut it down and watched it slowly creep back up. The first time it did it, I fired it back up and cooled it down longer. Who knows how many times it has done it in the past.

 

[rbattelle]

Ryan, did you ever measure the temperature of the turbo housing/exhaust manifold itself?

No, but I could easily do so... I have a thermocouple. I suppose I should.



-Ryan