I have a 1999 1 ton with the 24 valve Cummins and 5 speed and pull a 30 fifth wheel camper.<br>Last year it started overheating so I put on a new fan clutch and it seemed to solve the problem.<br>We went on a 4100 mile trip over mountains with no problem. (of course this was in Oct with no real high <br>temps).<br>Last week we went on another trip and it started overheating again just like it did before I replaced the fan clutch.<br>These were hot days and it seemed like it would overheat when we had a wind at our back more than any other time.<br>If I would shift down and keep the engine revved up to about 2600 it would cool down enough that the light would go off.<br>but still run very hot.<br>I have had people say they can hear the fan clutch when it comes on but I can not (maybe because of the diesel noise).<br><br>What can I do to solve the heating problem??? Would the fan clutch have gone bad again already?<br><br>Thanks for any help as I am getting tired of this!!!!!!<br>

 

When you say overheating, how high does the temp gage go up? Diesels like heat, 3/4 gage is not to hot for them. I would look at the following if it is really overheating I would do the following: make sure you have a good airflow thru the rad, bugs like to plug the air as does the oil from the vent, i would look at a new thermostat and a cooling system flush and a fresh fill, between 50 and 65% max.<br>

 

It gets really hot.....the warning light goes on and the temp gauge goes over to about 230 and I have to pull over and let it cool or even tho it is not working the engine sometimes if I drop a gear it will cool enough for the light to go off but still runs about 210.<br><br>I have cleaned the radiator fins out and checked the water mix and all that stuff but have not chaged the thermostat.

 

I'd change the t-stat for starters. <br><br>But is the radiator plugged up inside? Inhibiting coolant flow? How did the coolant look when you flushed it?

 

Flush the cooling system and get a new thermostat, Cummins part no. 3935811. $16.88 at your local Cummins Dealer.

 

thanks all.....will get a t-stat and flush

 

To check the fan clutch, turn the fan when the engine is not running. It should be stiff to turn. If it spins freely, it needs to be replaced.<br>If the fan clutch kicks in you will hear the rush of air from the fan building up speed. You should have no problem hearing this over the diesel, even more so at higher RPMs.<br><br>If you are moving at 30+ MPH, you should not need the fan anyway as there is plenty of air getting through the radiator at that speed or above. If this overheating is occurring at 30+, you should look for another problem first, like the other suggested.<br><br>Chris

 

One more question, do you all recommend the 190 or the 180 <br>degree themostat?

 

I tried to buy a 180* from Cummins and they wouldn't even sell it to me since the engine was in a Dodge. If you can find a way around that, then I'd go with the 180* in the summer time and a 190* in the winter.

 

Now I am really confused.....from what I have read, I thought part #3954194 was 180 * and part 3935811 was 190*.<br>I went to my friendly??? cummins dealer today and tried to get a 3935811 and he said it converted to a 3954194 now.<br><br>So I think he is saying that the 190* is no longer available??<br>Only the part # is on the box so I don't know if it is 180,190 or what.<br><br>Any ideas about this?

 

As someone else said, diesels like it hot. I'd stay with the 190. I put 190 or 195 in my gassers too.<br><br>Chris

 

I wanted the 190 but according to the parts person only the 180 is available???

 

Sorry about so many questions, but does anyone know if the 190* t-stat is still available or was this parts man just trying to make a sale and feeding me a bunch of bull?<br><br>This is the only cummins dealer within about 100 miles.

 

I don't honestly know, myself. I would probably just go to NAPA or other parts store for my thermostat. Stant is a really good brand if you can find it.<br><br>Chris

 

Regarding the fan clutch, you should hear the fan start to &quot;roar&quot; (for lack of a better term) as the temp goes up, particularly on grades. If it heats up on a grade, the settles down, I doubt it's the thermostat. If you are feeling really ambitious, get two temp gauges, one on the lower hose and one on the upper hose and observe the difference when the engine is overheating. Low temp difference = poor airflow. Big temp difference = poor coolant flow.