Cummins Diesel Forum banner

Running cool

2K views 12 replies 8 participants last post by  illflem 
#1 ·
Generally speaking when driving down the road my truck will run really cool (170ish). It has run real cool when it was in the dodge and now it's in a gmc. I put in a new thermostat, and no change. It did run about 195 when it was 105 out this summer.

Any suggestions to get it to run warmer?
 
#2 ·
Cover up a portion of your radiator. The 12v has a thermostat bypass that allows some coolant to circulate through the radiator all the time.

I used to never reach 190 on my 30 mile commute when overnight temps started dipping to around 40, so I made some solid inserts that attach to the honeycomb portion of my grill, blocking almost all the passive airflow from the front. There's a 1/2" or so gap between my bumper that still allows air in, and the fan can suck as much air as it needs up from behind the bumper. Now I hit 190 after 8-10 miles on the highway and the temp doesn't bounce between 170 and 190, maybe 180 and 190.

I've also ran with the grille inserts in with outside temps as high as 65 and the stock fan kept it right at 190. I'll take them out when daytime highs start getting above 70 or when towing/hauling, but for empty driving you don't need any passive airflow.
 
#3 ·
That makes since because when I pulled into a convenience store after 1-1/2 hours of driving, the temp started raising. Got back onto the highway and dropped back down.

What's everyone's thoughts on putting a valve on that bypass that you could close during the winter?
 
#4 ·
Most older diesels have 172deg t-stats with the clutch fan reaching full lockup around 195deg, check your fan if it's pulling too much air your going to run cool. Covering part of the radiator will help maintain temps, we had winter fronts on semi's so the engine would run warmer and knock the chill off the firewall so the cab would be warmer. The bypass hose is only a 1/4" and it helps prevent the t-stat from air locking if you get low on coolant.
 
#9 ·
I'd disagree with the idea of ignoring low coolant temp as it means a low engine temp. I can see ignoring 170+ but if you have a truck that barely squeaks into the operating range it'd be best to do something about it.
 
#7 ·
Question: My old '95 just started running cool about 2 weeks ago, so I guess the thermostat is sticking open. Running around 140-150ish after 40 mile trip WITH winter fronts on and I have no real heat to speak of. Until now, for the 5 years I've owned it, it has warmed up fairly quickly and stayed at temp no problem.

I just picked up a new thermostat today but they didn't have the inner and outer seals, if ordered would be in stock in a couple of days. Do I have to have these seals or not?

I just wanted to save myself another 100 mile round trip to town if I didn't absolutely need the seals.

Thanks,
Kent
 
#10 · (Edited)
it'd be best to do something about it.
You could always buy a '98 and see what Cummins did about it, electronically make the gauge into an idiot light.
Obviously they didn't think it was much of a problem or it would have been addressed much sooner.
The real problem is a lot of people don't use these trucks for what they were designed for. Sort of doubt Dodge or Cummins thought many people were going to use the $3000 diesel engine option for cruising around empty.
Hook a load to it and the temp will come up and quit fluctuating.

My two 500 hp plus JD tractors and combine will all run right where the blue (cold) and green(normal) gauge areas come together all day until you put a load on them.
I see it as good engineering.
 
#11 ·
You could always buy a '98 and see what Cummins did about it, electronically make the gauge into an idiot light.
Obviously they didn't think it was much of a problem or it would have been addressed much sooner.
The main problem is a lot of people don't use these trucks for what they were designed for.
Hook a load to it and the temp will come up and quit fluctuating.
__________________
I have no problem with that, however most of us don't tug around a load everyday so might as well get it to warm up.
 
#12 ·
My 98 12v fluctuates. Maybe just the 24vs? My 91 toyota had the same idiot light for a gauge function problem. I was able to fix it by replacing a diode with a resistor in the gauge and it is now a functioning gauge again.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top