running too hot, running too cold!

[jaynes]

Boy I'm on a roll with posts,lately!



My non IC '91 runs really hot in the summer, and really cold in the winter. Empty. I remember I was doing some storm chasing last summer, it was about 80-85 degrees outside, and I was going around 75-80 mph, running empty. My temp gauge climbed so high that I had to slow down to 65-70 mph, just too keep it cool. Does the same thing around town during the summer. In stop and go driving, I usually have to resort to idling it up in neutral to keep it cool. Sound like a thermostat stuck closed? But what about winter?



In the winter, the heater doesn't heat very well... or sometimes not at all, depending on how cold it is (card board helps), the engine never gets warm. Maybe this is closer to normal than the over heating thing, but i was just wondering. Almost kinda feels like the termostat is stuck open!



When the engine gets hot, the idle drops. I don't have any excessories (like a/c, well I do but it doesn't work) that could bring the idle down. My fan clutch is working, I can hear it kick in, and it does that alot in the summer. When the engine gets hot, the idle drops really low. After a drive on the highway for about an hour in the summer, if I pull off somewhere I have to keep my foot on the gas to keep the idle up to where the oil press doesn't drop to 0 and the light doesn't come on. What gives? Anyone have an idea? I raised the idle some, but i don't know how much good that did. Sorry for the length!!



Jaynes

 

[dodge cummins]

just replace the thermostat! it will only take you a hour including a full flush of coolant. the thermostat is about 20 bucks from cummins. you can get a direct replacement thermostat from tst. turn your idle up to 800 rpms with a/c engaged and in drive and that should take care of idle issue.

 

[jaynes]

I'll try that once it starts getting warmer out. I was going to replace it anyway, I just didn't see how the engine being hot would have an effect on the idle. Infact, when I got the inj. pump rebuilt, and we fired it back up, it sounded like it was idling low. They told me that had it set at 700 rpm, just like factory specs. I said it was too low, so they bumped it up to what sounded like quite a bit. Not sure what it is now... man I need a tach!



josh

 

[Paychk]

Josh



Do you have the cross flow style radiator? easier way to ask is your truck factory intercooled? It sounds like you have the old style radiator and they were know for short cycling the coolant. That would explain the the overheat in summer, but might not explain the no warm up in winter.

 

[RWWinslow]

Thermostat is probably a bit of a culprit in the winter. . . for the summer overheating conditions I would check the following:

1) Is the fan clutch still operational - sometimes when they fail the clutch will still appear to be turning the fan but not enough to pull air across the radiator.

2) Check your radiator exterior for pluggage. The old verticals will plug up with bugs, etc. I have found that mine will start running hot if it bugs up and plugs about 20% - they wash out pretty easily if you clean them regulalry.



3) Check the water passages for corrosion deposits / pluggage. If water other than distilled was used in the anti-freeze water mix, then you will have deposits built up that will plug the water passages.



4) Is your fan shroud still on? If the shroud is off, this will really heat up the radiator - especially the vertical flow ones.



5) Is your A/C condenser coil plugged up with bugs or mud?



Normally, the early 91's did not have a real big problem with overheating since there was no inter-cooler on the front. . . . . that said, you can still find a new replacement radiator at a fair price.

 

[TKingsbury]

I think I'd lean toward the thermostat. In the winter, the water circulates too fast and the rad cools it good because of low ambient temps. The water won't stay in the engine long enough to heat it. In the summer, the water doesn't stay in the radiator long enough to cool it when the ambient is too high. If your radiator were plugged, it'd overheat all the time.

Travis. .

 

[jaynes]

Fist thing I'm gonna do is buy a thermostat. While i'm at it, i'm going to check the radiator for plugage, and also get a radiator flush. I don't know how to check for deposists in the water passages, though. Thanks for the replys!



jaynes

 

[bgilbert]

Cummins stat ONLY. Do a search for the updated part number, it will not have the temp fluctuations. I'll post after some sleep on the running too hot/cold.

 

[cerberusiam]

First question would be are the high readings the stock temp gauge? If so put in a mechanical and verify that the temp is actually too high. The gauges in the early models would some times read hot when they were not.



I would suspect the thermostat is stuck partially open from the symptoms but verify the temps are actually getting too high before chasing a gremlin.

 

[BushWakr - RIP]

I'm gonna tip my hat in with most of the suggestions made above and, in particular RWWinslow's sequence of things to check/do.



I also suspect that your high coolant temps may be the cause of you idle drop... it has been something I've scratched my head over once or twice myself... it seems that when I really wail on the old girl, get her good and hot (EGT's) and push max fuel thru the thing the VE gets VERY hot... when this happens the idle becomes a bit unstable and seems to drop or "rump, rump" like a big cam gasser... after a while it cools and stabilizes... it may be coinscidence or it may not... but I have reproduced it.



When I came across this, I went to a more generous amount of additive in the fuel...

It 'seems' to have helped a tad...

When you have a chance and the system is hot like you describe, jump out (when you're stopped of coures ) and try to put/hold your hand on the VE pumps' body... you'll see what I mean when I say it gets HOT... which by the way, thins out the fuel too.



pb... .

 

[BHiggins]

I replaced three fan clutch's in my '90 for the same reason. Big mistake. It turned out to be the radiator. There were several rows in the center of the radiator that were clogged. No overheat problem ANYWHERE until I got on a big hill pulling a big load. The fan never came on... ever. It turned out none of the middle rows of the radiator "blew hot air" on the spring that locks the fan clutch.

Warm the truck up (get it hot) then, shut it off and run your hand across the radiator. You may feel a "cold spot" like I did.

 

[JLEONARD]

Josh,

Good idea to check the radiator for hot and cold spots. .

My non I/C top flow radiator equipped 91 runs a very even temperature... according to the gage... it doesn't vary more than the needle width once it comes up to temp... summer or winter.

I get awsum heat in the winter... blasts me out of the truck.

Jay

 

[RWWinslow]

More I think about your problem, and the experiences with my truck, I believe, from your description, that you might have more than one problem - not uncommon with these older trucks that are pushing the mileage envelope.

 

[jaynes]

hmmmm..... quite a few things I can check out