EGT and Coolant Temp Question

[Brooklyn Tow]

Could anyone explain the relation between EGT's and coolant temps?

If you see high coolant temps 210* and higher, what would this translate in EGT temps and vice versa? when your egt's start climbing, do you notice an increase in coolant temps?......Not looking for specific #'s, but in general, is/how much of a relationship is there between the 2?

Obviously this quetion is for the attentive gauge watchers.

 

[ak diesel driver]

anytime your egts go up it will affect the engine temp but it is possible to have high engine temps without "high" egt. faulty cooling system. I've never had a cooling issue but last summer towing my 26' TT I could see my temps go up a couple of ticks when on a big hill. Saw some 900-1000* egts then. Might have seen higher but the hills weren't very long.

 

[bison]

I also never had a cooling issue yet,might be cause there aint no AC on my trucks and i got the cooler T-stats.
Egt's run up to 1100 on a hard pull uphill without affecting the Engine temps really noticeble on both heads CTS'ses,highest i seen is 90 degree C. The EGT's drop considerable and fast once i take my foot out of it or i crest the hill.

 

[schiker]

They are temperature indicators of the heat dissiapation balance.

The heat comes from fuel burn. When load increases (towing, hill, head wind etc.) you add fuel to keep speed or accelerate. This adds heat to the combustion chamber and EGT will climb. EGT will track but with some delay with fuel pedal pretty much exclusively. Intake air cools EGT and boost has a relation but pretty much EGT tracks with fuelrate. No load idle EGT should be very low <300F, city driving only a little fuel EGT will range 300-500F. Cruise interstate with 70mph EGT might range 500-650 ish depending on turbo and exhaust etc. Loaded or hill climb with foot on 3/4 pedal it will range upwards of 800+F Then depending on truck setup max pedal EGT might climb 1100F or higher.

ECT is even slower but will also track behind EGT. The combustion chamber radiates most of the heat into the head. If the radiator has the capacity to reject all the heat then ECT might not move. But usually it will increase some depending on ambient and what numbers you talking about.

ECT numbers are all over the place depending on ambient, number ranges you would like to discuss, and condition of cooling system:
Simple: As heat is generated the thermostats will open and close to maintain ECT in the head/engine at operating temp. Anything under EGT 500F ish the cooling system should handle w/o any change in ECT due to stat modulation. Increase fuel thus heat and the radiator warms and the stats will stay open. More fuel equal more heat and once radiator heat soaks ECT will increase. As delta air and ECT in radiator increases so does heat transfer to the air increases. Once ECT climbs in radiator the fan clutch will engage to increase air flow over radiator and increase heat removal. If air increase doesn't remove heat ECT will continue to climb.

You did not mention boost but that will track even faster with foot pedal. Fuel equals heat which drives the turbo. IAT will track with boost and depends on system. Oil temperature will track somewhere behind ECT and lastly oil pressure will track behind that if oil temperature increases considerably.

 

[Matt Bachand]

I would think Oil Temp would track more closely to EGT than behind ECT considering its lubing and cooling the combustion area at the heart??? Schiker you have both gauges going? Always wanted an oil temp gauge, but afraid of causing an oil leak to install one.

But yeah, Don't think its possible to raise ECT off of its operating range, without raising EGT's first.

 

[Brooklyn Tow]

They are temperature indicators of the heat dissiapation balance.

The heat comes from fuel burn. When load increases (towing, hill, head wind etc.) you add fuel to keep speed or accelerate. This adds heat to the combustion chamber and EGT will climb. EGT will track but with some delay with fuel pedal pretty much exclusively. Intake air cools EGT and boost has a relation but pretty much EGT tracks with fuelrate. No load idle EGT should be very low <300F, city driving only a little fuel EGT will range 300-500F. Cruise interstate with 70mph EGT might range 500-650 ish depending on turbo and exhaust etc. Loaded or hill climb with foot on 3/4 pedal it will range upwards of 800+F Then depending on truck setup max pedal EGT might climb 1100F or higher.

ECT is even slower but will also track behind EGT. The combustion chamber radiates most of the heat into the head. If the radiator has the capacity to reject all the heat then ECT might not move. But usually it will increase some depending on ambient and what numbers you talking about.

ECT numbers are all over the place depending on ambient, number ranges you would like to discuss, and condition of cooling system:
Simple: As heat is generated the thermostats will open and close to maintain ECT in the head/engine at operating temp. Anything under EGT 500F ish the cooling system should handle w/o any change in ECT due to stat modulation. Increase fuel thus heat and the radiator warms and the stats will stay open. More fuel equal more heat and once radiator heat soaks ECT will increase. As delta air and ECT in radiator increases so does heat transfer to the air increases. Once ECT climbs in radiator the fan clutch will engage to increase air flow over radiator and increase heat removal. If air increase doesn't remove heat ECT will continue to climb.

You did not mention boost but that will track even faster with foot pedal. Fuel equals heat which drives the turbo. IAT will track with boost and depends on system. Oil temperature will track somewhere behind ECT and lastly oil pressure will track behind that if oil temperature increases considerably.

Thanks for the descriptive answer.....Good info for 6.5ers with no EGT gauge, like myself.

ECT is not a good EGT indicater.

 

[midniteplowboyy]

If you have the low flow water pump your generally safe on EGT's if your below 210ºF water temp. With the HO pump its best to have an EGT gauge, one might be higher than the other.

Engine oil temps dont fluctuate as quick and are not a good indicator.

 

[Brooklyn Tow]

If you have the low flow water pump your generally safe on EGT's if your below 210ºF water temp. With the HO pump its best to have an EGT gauge, one might be higher than the other.

Dual Stat and HO pump here....Good added info, to keep in mind.:thumbsup:

 

[Matt Bachand]

I disagree with the above statement. Your EGT's can go from 500-1000+ in about 10 seconds with heavy throttle climbing a big hill. Maybe faster depending on how hard your pushing it, and how much fuel you output.

As long as your not really working the truck, the above statement is a good generalization.

BUT, considering your a Tow Truck, and varying unknown weight/drag loads, your EGT's could get real hot really fast without you knowing it.

 

[NVW]

My truck never over heats but I can get high EGT's, I would agree that high CT would raise EGT as will high IAT.

 

[midniteplowboyy]

I disagree with the above statement. Your EGT's can go from 500-1000+ in about 10 seconds with heavy throttle climbing a big hill. Maybe faster depending on how hard your pushing it, and how much fuel you output.

As long as your not really working the truck, the above statement is a good generalization.

BUT, considering your a Tow Truck, and varying unknown weight/drag loads, your EGT's could get real hot really fast without you knowing it.

Maybe its a Texas thing with it being hotter down here, but my water temps can go from 150-230ºF in about ten seconds also, even with the HO, because these engines aint got enough water pump for the IDI head design. I've seen 100-125ºF temps going in at the rear of the head and 230ºF at the other end coming out with safe EGT's, but this is not on a stock engine.

With the low flow pumps, temps fluctuated more because they couldn't move as much heat, they'd go up/down like a pyrometer on hills with a load, even with stock fuel you could put one way past 210ºF easily. With the HO pump, it will keep a stock fuel engine water temps safe, this is where you need the pyrometer.

My 92 had crack free heads at around 200k when I replaced the head gaskets. Atleast 125k of those miles was towing 6-18k depending on empty or loaded weights. I'd run it up to 210º then start backing off the go peddle, I'd run it to 220º but not under full fuel, after 220º I'd back all the way out. This was the low output water pump though, if I'd had the HO I might have melted the pistons or cracked the heads because the water temps looked safer.

 

[Matt Bachand]

Maybe its a Texas thing with it being hotter down here, but my water temps can go from 150-230ºF in about ten seconds also, even with the HO, because these engines aint got enough water pump for the IDI head design. I've seen 100-125ºF temps going in at the rear of the head and 230ºF at the other end coming out with safe EGT's, but this is not on a stock engine.

With the low flow pumps, temps fluctuated more because they couldn't move as much heat, they'd go up/down like a pyrometer on hills with a load, even with stock fuel you could put one way past 210ºF easily. With the HO pump, it will keep a stock fuel engine water temps safe, this is where you need the pyrometer.

My 92 had crack free heads at around 200k when I replaced the head gaskets. Atleast 125k of those miles was towing 6-18k depending on empty or loaded weights. I'd run it up to 210º then start backing off the go peddle, I'd run it to 220º but not under full fuel, after 220º I'd back all the way out. This was the low output water pump though, if I'd had the HO I might have melted the pistons or cracked the heads because the water temps looked safer.

What were your EGT's during these runs?

I guess its all how you drive too... and each load will be different... as will each truck .... and each road....


You can directly control EGT's with your right foot. Without a guage you should worry only when really working it.

 

[midniteplowboyy]

What were your EGT's during these runs?

I guess its all how you drive too... and each load will be different... as will each truck ....

I have no ideal, I didnt have a pyrometer, this was back in the 90's before I had internet/forums and all this useful info.

Dont worry she's finally getting a pyrometer, along with new IP, injectors and glow plugs, just got to put her back together.

 

[Matt Bachand]

I guarantee my truck wouldn't be here today if it wasn't for these forums.... 100%. I would have overheated it to death road tripping with the plow.

Then again it had 85k of sheep driving it with a badly rotted plow so you know it got used... so who knows.



I sure as hell wouldn't have a pyrometer either

Or even think of EGT's.....

 

[bison]

I guarantee my truck wouldn't be here today if it wasn't for these forums.... 100%. I would have overheated it to death road tripping with the plow.

Then again it had 85k of sheep driving it with a badly rotted plow so you know it got used... so who knows.



I sure as hell wouldn't have a pyrometer either

Or even think of EGT's.....

you can count me in on this.

i been farting around with diesels all my life, never gave the EGT's a thought :rolleyes5: before i hit these forums.:thumbsup:

 

[Brooklyn Tow]

you can count me in on this.

i been farting around with diesels all my life, never gave the EGT's a thought :rolleyes5: before i hit these forums.:thumbsup:

Exactly why I asked.....Without a EGT/Pyrometer...It's kinda' like, trying to hear a mouse piss on cotton in China.

 

[bison]

As far as that goes ,stupid automotive diesel truck builders should've made them EGT/boost/fuel pressure sensors/gauges standard equipment.
Morons think only about their own bottomline.

 

[WarWagon]

As far as that goes ,stupid automotive diesel truck builders should've made them EGT/boost/fuel pressure sensors/gauges standard equipment.
Morons think only about their own bottomline.

:nono: Although you have the right idea it will not work for the lowest common denominator. Aka stupid people.

Do you know how many warranty claims and complaints GM would get from "bad" gauge readings because people don't understand the gauge?

The mere example of the numbed temperature gauge on the Duramax and further the numb oil pressure gauge is what they are thinking. 9 PSI "stop engine alarm" and 35 PSI read the same on the gauge. The 40 degree ECT gauge numb spot is well documented.

On topic:

Oil temperature also follows load. Not related to EGT exclusively as other factors like RPM affect oil temps. Downshifting at the same speed and load can raise oil temps 25 degrees.

You should watch trans temps and engine oil temp. If you overheat the engine oil you can scuff a piston and then it is only time before you are pulling the ruined engine out.

 

[schiker]

My last job I had the opportunity to heat balance test small diesel engines to see if radiator, enclosure, and overall application was acceptable to the manufacture to provide warranty. It was mainly Kubota and Yanmar I worked with but I had some info from Deutz and had some info from another company also doing some similar application. We would thermocouple up bottom and top radiator hose, oil pan, EGT, intake air (at filter) and air temp around engine, air temp in front of and behind radiator, and air flow through radiator.

Truck loading is very dynamic and you can see different stuff at different times. My testing was more steady state and measured the trend and peak temperatures after max load was established over enough time to determine it wasn't going to overheat.

The thing about oil temp I saw was it can change fairly fast but especially when you are near heat balance it can continue to climb slowly after reacting to the load. And it can take a long time to peak out if there is not enough oil cooling capacity and radiator is near balance too (up to 20-45 minutes after ECT has peaked). Too long for most all vehicle guage applications.

I suspect (but have never been told or read anything) but its because really high oil temp comes from the "flash" loading of exposure to the piston crown. Like running your finger through a candle flame. During this spray cooling or pass by the piston the oil is exposed to temps upwards of 600-800F or more - way past the typical break down temp of oil. Also the flash past the turbo can expose it to really high temps for a short time but oil doesn't break down and engines seem to live fine with the oil doing this "flash loading".