Puke

Lately, (with my 98 24 valve) I've noticed when I'm stuck in very slow traffic, that my temp guage is going up quite a bit...seems to be at 220 or so until the speed picks back up again. Did it yesterday and it was only 85 deggrees outside.
I don't recall this ever being the case until this summer. (not too many traffic jams here in Salt Lake). Usually (even when towing, etc.,) It has always sat just above 190 degrees...with a max at maybe 205 or 210 if I'm towing and climbing a long hill in very hot weather (like going to las vegas in the middle of the summer).

So this has me purplexed. If these things had electric fans..i'd think the fan wasn't working, but since it's not electric, I'm not sure what to think?? I mean, I have no idea whatsoever. About 2 years ago I replaced the thermostadt because the old one was staying open and the truck was not heating up. That's all I can think of right now.

Ok,
Anybody out there who might have an idea on this, please chime in. I don't even know where to start. The radiator level is OK, etc.,

high bid

Check the easy stuff first.
1. plenty of coolant
2. possibly a water pump going bad
3. I've read that the thermostat s/b purchased from the dealer or genos

duster75

Clean the rad. fins are plugged up on the outside. When you replaced the stat. did you replace with a cummin's 1? I've read on here that people have problems with over the counter 1's. Nate

Totallyrad

4. The area between the radiator and the condenser is plugged with bugs and trash.

Junk Man

AND you must pull the radiator to properly clean it. I have 30,000 mi on a clean radiator with no problem and haven't relocated the puke bottle.

Other likely culprit is an aftermarket thermostat. They will cycle up & down unlike the Cummins part which costs more but is rock solid.

Puke

My new thermostat was over the counter but wasn't cheap (was on a weekend,...I doubt it was an official cummins..
The old one took much much longer to let the truck warm up, ever since it was new it seemed like ten miles or more to warm up. I liked this one because my heater would get warm by the time I got to the freeway onramp to go to work.

OK, I guess I better check the bug thing between the radiator and a/c condesor unit.

Tacomaman87

It sounds to me like the fan clutch is not working. fas is not turning then when you take off air flowing through the rad cools it back down

Puke

Is there a "test" to see if the fan clutch is working?

Junk Man

I've had at least 3 aftermarket tstats installed & they all cycled. Cost was ~$35 which is too much. The only thing they were good for was the gasket which isn't available stand alone from Cummins. I used the gasket on an old OEM tstst & problem solved.

KATOOM

Yes. With the engine off, grab a fan blade and try to turn the fan. It should offer plenty of resistance and not spin freely. While holding the fan blade you should also take note if there is any free play in the fan. It shouldn't wiggle or move forward and back. Then when the engine is running and its hot out, you should clearly hear the fan roar when the engine RPM's are up. If the engine gets over 195*-200* and you dont hear the roar of the fan then the clutch fan is not working properly.

BUT.....I'd bet that you never relocated the engine crank vent tube which exits right between the engine and the radiator. All that oily blow by venting out is being tossed around by the engine fan and causing the radiator to collect oil residue, dirt, and bugs, eventually clogging a good portion of your radiator and seriously reducing the cooling ability. Its not obvious to see a plugged radiator either since you're looking through the A/C condenser and the aftercooler, but a good give away is engine fan blade edges all gunked up, dirty oily residue on the front of the engine and radiator.

Puke

OK,
Is there a place to get a cummins thermostat during the evening or weekend??? I guess I'll go get one. Maybe I'll end up online or something.
I do remember that little gasket thingey.

As far as the engine crank vent tube. In my case highly unlikely. I use one can of gunk degreaser on the engine and compartment every time I change the oil. There is little or no residue build up. Mine looks extremely clean compared to the regular "off the street" truck. (The outside of the truck may look like hell, but not the engine compartment.) Thanks for the responses.

KATOOM

Its highly unlikely its your thermostat. But if it helps you sleep at night go and get another one. I changed my bad thermostat with one I got at NAPA and I never had an issue. The only thing I've heard mentioned is that sometimes the cheap replacement thermostats can restrict flow because they have smaller openings. But thats not going to be why your truck gets hot in traffic. Your problem is air flow. So its either the clutch fan or a dirty radiator. Again, since you never relocated the engine vent tube (which is notorious for creating this issue) I'm leaning toward that being your problem. I dont care if you use engine gunk everyday. The problem is not on the surface but inside the radiator fins where you're not looking.

Russ Roth

Katoom,

Generally I agree with everything you have stated except for the vent tube. Ours do have it up by the radiator but if I am not mistaken my two buddies '98.5 and '99 have it on the side of the block. Still very well could be a blocked radiator and sometimes the only way to tell is pull it.

Mine started heating more than normal pulling my TT last winter and the backside of my radiator looks very clean but I'll bet it isn't. I had another buddy with a 2000 that I saw last hunting season. He complained about it heating so bad on the way up. I asked him about the vent knowing he wouldn't know and when we looked at it he knew immediately why his was heating. His is at the front just as ours is and the radiator looked to be about 60% plugged.

KATOOM

Very good point Russ Roth. Pre 2000 models do vent on the side instead of the front.
The OP could very well have a bogus thermostat but the reason I doubt it is because a bad or insufficient thermostat wouldn't allow the engine to cool back down when the speed picked up. Maybe I'm wrong here but that clearly sounds like an air flow issue.

Russ Roth

I agree that's what it sounds like. I just wanted to point out not all the 2nd Gens have the puke bottle on the front. Radiators still can get clogged though.