I plan to install an exhaust gas temp gauge on my 2002 GMC Sierra 2500HD duramax/allison, since I routinely tow a 7,000# travel trailer, and I know how important it is not to coke the turbo when I shut down after long sessions on the highway. My question is: should it be installed pre or post turbo? The one truck store I've talked to so far had to call someone and ask how to install it, while I was standing there listening to him make the call! Talk about not instilling confidence in his level of expertise doing the work! Needless to say, I didn't hire him to do the job!
I installed my own pre-turbo. Shows what the turbo is ingesting and responds quicker to changes. Post turbo is really only good for knowing when the turbo is cool enough to shut down, but I generally just wait a few minutes to cool down when towing. You can still see the temp dropping off gradually when "cooling down", you just have to remember that the turbo is lagging behind a bit...
EGT pre or post turbo question #2 I see from the excellent answers I got to my first question (pre or post turbo; ans: pre) that I don't know enough yet to ask all the right questions! So here's my second one. The main reason I thought I wanted to measure EGT is to be sure I let the temp of the exhaust gas drop to 300 degrees or less before shutting down the engine after a long towing session. Or is it the temp IN the turbo that I'm supposed to get to 300 or less? In other words, exactly what point in the entire system is it that I'm trying to get below 300 degress before I consider it safe for the turbo to shut down the engine? Depending on exactly WHERE I'm trying to achieve 300 degrees, I'd have to interpret the gauge reading differently if I put it pre or post, wouldn't I? In other words, if it was pre, 300 would mean the TURBO woudl be under 300, so I'd be safe in shutting down. But if it was post, and I wanted the TURBO to be under 300, I'd need to wait until the gauge measured something less than 300 to be absolutely safe, wouldn't I? See how confused I am!
Actually, pre-turbo temps drop faster than post turbo due to the heat soak of the turbo itself, just like they also rise faster due to the turbo absorbing energy. So, you are right to say you interpret the values differently. As I said earlier, the pre-turbo temps respond faster due to the turbo soaking up and releasing heat as it "chases" the pre-turbo temps. But it's really not a huge deal and nothing to get too focused on. Basically, your pre-turbo temps will drop fairly rapidly to the "cool" range of 3-400, then you let it idle a bit so the "cool" gases can cool the turbo housing a bit. Something like 30 seconds to a minute after dropping below 400 or so is generally regarded to be plenty with the cooling effects of oil circulation and exhaust gas combined. If I'm pushing 12-13k up a long grade, I would probably wait longer just on principle, but it's really not necessary. In fact, GM (and others?) actually say that NO cool-down is required, though chips do bring up the EGTs higher than the factory spec'd. Hope that helps…
That reason for a pyro is minimal vs. what most people use a pyro for. If all I was worried about was shutting the truck down I wouldn't spend the money on a pyro. After pulling hard let the truck idle for about 2 minutes and shut it off. If the truck is empty you don't need to wait hardly at all, I don't. The real reason for a pyro is to monitor the exhaust temps to keep from melting the motor while in tow. Generally, when a truck is stock the EGT's while pulling a grade should be fine. Millions of stock diesel pickups tow grades every day without heating issues, because they are stock and the engine is set up correctly from the factory for the right amount of air vs. fuel that won't exceed safe EGT's. If you have a chip than you need the pyro, now the motor is getting more fuel than stock which means more heat, many times this is more heat than the stock turbo can take for an extended "pull." Anyway, pyros are for monitoring your EGT's while pulling, so you know how hot the turbo and head is and if you have to back off it or not. A pyro seems like an expensive tool for just turbo cool down.
EGT's I installed a EGT guage, pre-turbo to keep an eye on the temps going into the turbo after installing an edge EZ. My modifications increased power for towing and increased EGT. It's my understanding you don't want to run over 1250 or so for a prolonged period so I need to watch the guage. I actually never knew about cooling down until I saw an ad for a device to control shutdown. I've had my truck over a year now and I learn something new everyday or everytime I write a check for repairs.
i installed the pyro pre-turbo on my 05 dodge (thats where the instructions with my chip said to put it). with the chip installed, the egt climbs right up to 1100-1200 or higher if im on the gas for too long. actually diesel power magazine tested a cummins w/ the edge juice w/ attitude and said that the egt got up to 1600 degrees while being dyno'd in level 5 . since the pistons in your motor are made of alluminum (which melts at around 1100 degrees i think) those of us with chips NEED a pyro in order to prevent damage to our trucks. in regard to cool down, i usually let the egt get down to about 350 before i shut down. in the owner's manual for the cummins they give you a guide to how long you should cool down depending on how you were driving. they say if you tow a heavy load on the highway for a long period of time you should cool down for a couple of minutes. if you're just driving around town then you dont have to cool down at all. i have heard that the whole turbo coking thing is more of a problem with older diesels or turbocharged gas motors but im not sure... check out myth #7 on the bankspower website... http://www.bankspower.com/tech_TD-fact-Fiction.cfm
Pre-turbo is the way to go on the d-max. Pull out the passenger side wheel liner and look at the manifold. In the manifold, just between the exhaust ports for the back two cylinders. It's realy easy, let the truck idle while you drill it with a sharp bit (step it up slowly - use a pilot bit then drill to size for your tap), and the exhaust will blow the pieces out the hole. Tap it carefully and thread in your probe. Use the money you save for a 4" exhaust. You should never have to worry about EGT's with a 7k trailer. Cool down, I subscribe to the "let it idle for a while after dropping under 400" theory stated above. Getting down to 300 takes a LONG time, and your d-max won't go down that far unless you shut off the A/C and let it idle for quite some time. At least mine won't. Marc Marc
haha ya my cummins wont get down to 300 unless you turn the air off and sit there for like 10 minutes
Glad to hear it's not just me! Seems that by the time any truck gets down that far, the cylinder walls will be washing down with fuel, potentially damaging other stuff over time...
