Engine/Transmission (1998.5 - 2002) Radiator super-cooled

[CCahill]

I put in a new t-stat recently, 'cause the truck wouldn't get up to temp... now it's gets up to temp OK, but yesterday I noticed when we were coming back from a day of snowshoeing... and on long downhills, coasting, the temp would drop to 150-160... then on the flats, or uphill, the temps came back up... that tells me the t-stat is not working correctly... like I say it's new, and wasn't cheap... any thoughts ?

 

[snuff]

do you use a cold front for the grill,?



also it could be the fan clutch, that has happened to be on my other truck,

 

[Alan Reagan]

Sounds cold outside. At idle and coasting, there is a lot of wind going across the radiator and engine. That will cause them to cool down like you describe. That's why these engines have to have a high idle when sitting still and not under load. When you are coasting, there is no load on the engine and it can't maintain it's temperature in the cold temps. The engine is very efficient and just doesn't generate enough excess heat under no load conditions.



As mentioned above, check the fan clutch. Otherwise, you can put a cold front on the engine to help reduce heat loss. I had to make an emergency cold front using a large cardboard sheet. I slipped it between the intercooler and radiator. Make sure if you do this that you cut a hole in the center so that if the engine does reach a temperature where the fan clutch engages, it can draw air through without over stressing the fan blades. Also, the intercooler does need some air flow to work properly.

 

[mhenon]

I wouldn't worry about the intercooler too much in really low temps. Cold air's nice when you want to make lots of power. When it's in the teens or below though you want to get as much heat to the engine as possible. I've got a cardboard winter front and re-routed air to the filter box so that it comes in from the engine bay. Even with that it's difficult to get IAT much more than 40-50 deg above ambient. At -10 deg and highway speeds I don't think you'll ever see the fan kick on.

Mike

 

[aircop]

Sounds normal to me, my truck does the same thing. Not as bad now that I have a cold front on it.

 

[analog]

I seem to remember reading somewhere in here that fuel to the engine shuts off when you are coasting. Am I smoking the good stuff, or is this legit?

I know when I head down a long downhill grade on one of the highways around here I regularly see my coolant temp (Isspro Guage) get down to 140-150*. I don't run a cold front. If indeed the fuel is shut off, there isn't much heat being generated if you are just coasting.

I do know my EGT guage goes down to below 200 on these long coasts.

 

[mhenon]

Foot off the accelerator and rpm above idle (coasting) and there's no fuel going to the engine. Just a giant airpump under those conditions.

Mike

 

[foolkiller]

my 99 did this for awhile. took for ever to warm up would cool down to the point of making the heater air luke warm on downhill runs. put a 195 (if i remember correctly 195) degree stat in it and it got better but it would still cool off a bit when coming down big grades in the winter.



my 07 does it too. not as bad but it does do it.



your situation sounds normal to me but t-stats are cheap and easy.



doubt it has anything to do with your intercooler though.



j

 

[2-ND TIME]

Radiator cooling

Sounds normal but. Before you replace the t-stat take it out and put it in a pot of water and use a meat therm and see if it opens at the correct temp? Even test the new one to see if it opens when it should. I have four pieces of baler belting hung infront of the rad to reduce air flow throught the rad. The air going throught the intercooler shouldn't be highter then 150*F then you only loose 1% power for every 10*F above that. Not much problem of that this time of the year. It is -40*C out this morning so hope I can get some heat out of the engine.

 

[Wyomingcowboy]

Not to offend anyone, but check to be sure it is in correctly. (Right side up) I only say this because I had the same problem so I bought a new T-stat from NAPA only to find the other one was in backwards!!! Saved me $30 and now my temps peg at 190 and stay there.

 

[Alan Reagan]

I seem to remember reading somewhere in here that fuel to the engine shuts off when you are coasting. Am I smoking the good stuff, or is this legit?



I know when I head down a long downhill grade on one of the highways around here I regularly see my coolant temp (Isspro Guage) get down to 140-150*. I don't run a cold front. If indeed the fuel is shut off, there isn't much heat being generated if you are just coasting.



I do know my EGT guage goes down to below 200 on these long coasts.

You are not smoking the good stuff yet. It is true, theoretically, that the fuel is shut off when coasting. However, as you can tell from the original post, the engine cools to about 140-150 and it will hold there so some fuel is being burned.

 

[cojhl2]

You are not smoking the good stuff yet. It is true, theoretically, that the fuel is shut off when coasting. However, as you can tell from the original post, the engine cools to about 140-150 and it will hold there so some fuel is being burned.

Don't forget friction.



On the same subject:

The old timers used to tell me here is an example of why exhaust brakes were originally designed. :: The engine internals cool way down going down hill then you light a 1700 deg fire at the bottom. What a shock. So make the engine work. Of course later Mr Cummins built what we now know as the Jacobs Brake, which still compresses the cylinder charge creating heat. (Seems that when the valve opens all work would be given up though)



Before exhaust brakes, we used to go down long grades with our foot on the air < 05psi and the other foot on the fuel feed to keep a small fire going.



Diesel engine by design ingests a full cylinder of air so with no fire all you have is friction to keep the heat up.



I would not expect the engine to stay hot going downhill. .



Most of this post is nostalgia I guess!!!



BTW, a SI engine works against a vacum so work is being done even going down hill. .

 

[DPellegrin]

The "friction" that is being talked about is the molecular friction of compressing the air charge. Even when there is no fuel injected and the engine is being motored by the inertia of the vehicle, TDC cylinder temperatures are still in the 1100F-1300F range depending on the speed of the engine. If the temps were not this high the diesel engine would never start.



Regards,