Engine/Transmission (1994 - 1998) coolant temp. will not stablilize

[MGarland]

Ok guy,s this is my first post here and I hope I am doing this correctly. I just bought a new to me 96 5 speed truck with 85000 mile on it and was doing some maint. on it and realized that the thermostat housing was leaking a little so I thought that I would get the new o-rings and a new t-stat and just replace the everything while I was in there. I get the job done and take it out for a test drive and the temp. guage goes to 190 deg. then it falls back to 150 deg. as the t-stat opens, everything seems to be fine except it keeps doing this 190 to 150 about every 2 minutes. I know that this can't be good on the motor with this much variation in temp. I took the truck to work and hooked it to our antifreeze reclaimer and purged the system backwards because I thought it still had some air in it. I took it out and drove it abou 40 miles and still the same, so I pulled the new t-stat out and out the old one back in, purged the system again, still the same. I then pulled the fan off thinking that maybe the clutch on it had failed and was locked tight because when the truck was cold the fan still moved a lot of air. It was still the same. I am now out of ideas and I need some help or suggestions, any ideas or experiences will be greatly appreciated. Thanks in advance

MGarland

 

[Mundgyver]

How is the water pump??? Is it pushing water?? Are the impeller blades intact or worn/corroded off??

 

[MGarland]

I have not had the water pump off yet because when the t-stat opens you can see the water moving in the radiator and I figured the the pump was working. Thanks for the reply.

MGarland

 

[Signal73]

Mine does the exact same thing along with others I have talked to. seems normal (believe it or not) in my book

 

[MGarland]

I hope that this is not normal because when it goes down to 150 deg. the heat goes to nothing and you can not regulate tthe heat in the cab very well.

MGarland

 

[Signal73]

oh yeah...

Found this on a nother post from HOHN:

It's NORMAL for these trucks, even with a new t-stat.



The reason is that the cooling system has such a large capacity. When the 'stat opens, it connects the 190° coolant with the cold coolant in the radiator. It doesn't take long for this mixing to drop the temp low enough to close the 'stat and whole process repeats itself.



If you're towing or working the truck, you'll notice this lessens or even goes entirely away.

 

[MGarland]

Signal73, Thanks for the info, I looked in the search section here and did not have much luck.

MGarland

 

[TRAMPLINEMAN]

Mine does it even when I'm towing.

 

[WDixon27]

i drilled a small hole in my new thermostat and it no longer cycles, i figured that the thermostat was too isolated from the flow through the bypass and was constantly being shocked by the temp changes, i drilled a couple 2mm holes so that coolant could flow around to the element and it stabilized

 

[Johnstra]

Did you ever figure out a way to keep it below 200*? Seems I remember you saying it stays constant but a bit on the high side.

-john

 

[mysteryman]

coolant

Today was the first cold day we have had in my area this year. My 93 was doing the same thing tonight... Drilling a hole in the t/stadt will help the problem. But to solve the problem all you need to do is cut a piece of card board and put in front of the rad. Cover 1/2 the rad first and see if it goes away... If not cover 3/4 of the rad... As long as it does not over heat you are fine..... The bottom line is that in the winter we just have too much cooling capasity... . The engine heats up , the t/stat opens up , the hot water goes out. then when the cold rushes in it instantly cools causing the t/stat to slam shut.....



Watch the big trucks this winter... ... you will notice that many will have the rad blocked off ... ... . Now you know why.....



I have a 68 Peterbilt with an 8v 71 in it... ... in the fall/winter while driving it gets up to 170 deg's. Then when I come to a red light the temp will drop to 100 deg's before the light turns green... . My Pete has automatic shutters in front of the rad... I have never even seen them open in the cooler months

Ok guy,s this is my first post here and I hope I am doing this correctly. I just bought a new to me 96 5 speed truck with 85000 mile on it and was doing some maint. on it and realized that the thermostat housing was leaking a little so I thought that I would get the new o-rings and a new t-stat and just replace the everything while I was in there. I get the job done and take it out for a test drive and the temp. guage goes to 190 deg. then it falls back to 150 deg. as the t-stat opens, everything seems to be fine except it keeps doing this 190 to 150 about every 2 minutes. I know that this can't be good on the motor with this much variation in temp. I took the truck to work and hooked it to our antifreeze reclaimer and purged the system backwards because I thought it still had some air in it. I took it out and drove it abou 40 miles and still the same, so I pulled the new t-stat out and out the old one back in, purged the system again, still the same. I then pulled the fan off thinking that maybe the clutch on it had failed and was locked tight because when the truck was cold the fan still moved a lot of air. It was still the same. I am now out of ideas and I need some help or suggestions, any ideas or experiences will be greatly appreciated. Thanks in advance

MGarland

 

[Grizzly]

I had the same problem with my 95 and was told by two dealers that it was normal.

 

[ttbird]

I have a 95 CTD and mine does the same thing. I have read here that Dodge or Cummins have developed a new and improved t-stat that stops the cycling but as mine has done this for many years I have not jumped to change it. I also use a cold front in the winter. Hope this helps.

 

[MGarland]

Thanks for all the good info and advice, I will be posting here in the future.

Thanks MGarland

 

[hsmith]

Normal for sure.

 

[K5IP]

Normal, yes. Still not good. I went through three of the upgraded thermostats before I finall foound one that does not fluctuate. I think drilling the small hole as suggested by WDixon is worth a shot, especially if you are thinking about changing it out again.

Even though most of these do move around, going down to 150 is too low. These engines need to be up to temperature to operate effeciently.

Rog

 

[biggy238]

I put a piece of cardboard in mine. This is on a new, unmodified t-stat.



It will still cycle, but it will be cycling "warm water" back into the block as opposed to cold water because the radiator isn't cooling it as much. This will cure the 60* drop every two minutes and give constant interior heat.



I wouldn't think the water pump could have died that quickly (85K) but it is still worth checking into. Try the cardboard first as it is most likely free.

 

[JThomas]

Water Temp

Hook 14,000 pounds of 5th wheel to your truck, and I'll bet the thermostat reading stabilizes real quick! Sure makes mine sit at 190 all day, even if 40 degrees out. What you are seeing is the result of the sensor being placed in a critical location. It is normal



J Thomas

 

[MGarland]

The truck has been pulling an 11000 poound enclosed gooseneck trailer and it will still still vary about 20 degrees an the guage. I hate to put any cardboard in front of radiator becaus it will also block the air from getting to the intercooler. I am going to pull the t-stat out monday after work and drill 2 holes in it and see if that makes any difference.

Thanks for all the great advice, MGarland

 

[WDixon27]

heres where i drilled mine

#ad


i haven't had any cycling since i drilled it, i have been drilling t-stats for years on the euro cars i work on for a living to help in bleeding but this is the first to get it to work properly