Higher EGT reading when engine is cold?

[Archive]

Well, I haven't been able to figure out this situation that I am observing. So, I have decided to see if anyone else has notices this.

If the air is less than 45 degrees in the morning when I start up my engine, the EGT (pre-turbo) goes up to 300 degrees within 5-6 seconds while idling. It seems that the temperature is higher when the engine is cold. If the air is warmer or the engine is warm, then the truck usually idles around 200 degrees.

It seems that one of the following must be true:

1) Exhaust temps are higher when engine is cold (or at least the measured temp is higher).
2) Gauge is not accurate or calibrated at these lower temps.
3) The voltage drop from the grid heaters are causing the gauge to show lower temperatures.

Well, I have not noticed any significant difference when the grid heater turns on or off. The temp before I start the truck is in a reasonable location on the gauge. I can't explain this and am wondering if I am the only person to notice this. Maybe my gauge is having problems at this temperature.

Thanks,
Tim

------------------
94' & 96' 2500 4x4, 12v, 5spd (Phx, AZ).

 

[Archive]

Tim,

Then ECM (Engine Computer) changes the injection timing and other things when the ambient air temperature is cold. This could be causing the higher temps.



------------------
98. 5 2500 QC LB 4x4 5spd, white. BFG 285x75x16
Cummins 24v w/ TST PowerMAX w/EGT and Boost gauges on A-Pillar.
SnugTop, JJ Stainless Running boards, Tow Hooks, Bushwacker Street Flares

 

[Archive]

Check the documentation that came with your gage and thermocouple. I think I remember that what is being measured is the difference between the air temp and the probe temp. I think it assumes 70 degrees or something like that and the gage is calibrated according the that assumption. So if it's 30 below it will be off a 100 degrees. Of course, when the engine is warn it's warming up the air under the hood so that would explain that observation.

------------------
Joe George
Eureka, CA

'95 2500 CC auto 4X4,Combo EGT/boost guage,custom switch panel,PacBrake,Torque plate,BD valve body,Automatic motorhome steps on both sides,Foldacover hard bed cover,Cummins chrome kit,Black steel grill guard,Front hitch receiver

 

[Archive]

I believe that Joe is correct. The thermocouple probe and gauge are calibrated for a certain ambient temp. When you deviate from that temp. it will appear that the gauge is readin incorrect.

------------------
Paul A. Schmidt
95, 4X4, SLT 2500, 5 spd. , 4. 10, 270 hp. ,675ft. lb. TST, AFC spring kit, Pacbrake, Walker muffler,
GearVendor O. D.
Eastern PA.

 

[Archive]

I agree with everyone, that the only explanation that is reasonable is the calibration explanation.

Sean: My truck is a 12v which has static timing!

Thanks for the responses,
Tim

------------------
94' & 96' 2500 4x4, 12v, 5spd (Phx, AZ).

 

[Archive]

I would guess that the engine and fuel being cold, that the burn rate of the fuel is slower in a cold combustion chamber and still burning as it is exhausted. As the engine and fuel warms the fuel burns faster and more completely in the combustion chamber before being exhausted. Just a guess on my part!

------------------
97 SLT 2500, 4x4, 5sp, 3. 54, 255/85/16. JRE #3 plate, JRE 300 hp Injectors, 16cm housing, Banks exhaust, K&N air filter, BD 60# exhaust brake, Isspro Digital Pyrometer and 50# Boost gauge, Centerforce Clutch, US Gear 20 % Overdrive, Rancho RS 9000 shocks, RS5000 steering stabilizer, Stull Stainless Steel Running Boards, Atwood Goose Neck Hitch, Alpine 3D Shuttle and Polk Audio speakers

 

[Archive]

I've noticed this on my truck as well. I think that it's the intake heaters. If you think about it the intake heaters are heating the air going into the engine to way above ambient air temp. Now it goes through the engine and comes out hotter through the exhaust. Let say the intake heaters are heating the air to say 120 degrees and the engine at idle at start up or after cooling down adds 180 degrees (the numbers are pure guesses) to that, it will give an EGT of 300. Now the intake heater goes off and the air going into the engine is at ambient temp of say 20 degrees and the engine adds the same 180 degrees you now have an EGT of 200. The reason I think this may be the case is if I start my engine cold my EGT shoots right up to 300 and once the intake heater stops cycling it drops right down to 200. Just a guess on my part.


------------------
-Steve St. Laurent - President of the Great Lakes chapter of the TDR
'98 QC LB (CMNSPWR), 4x4, ISB, 5sp, 4. 10 LSD, Prime-loc, boost & pyro gauges, TST Powermax, Permatech spray in liner, Grizzly ss nerf bars, front Draw-Tite receiver, BFG 285/75R16 AT KO's
http://my. voyager.net/stevest