Cooling conundrum, 2000 cummins 5.9L 24v

[-cycosis-]

So Ive had my rig for 7 years now. Shes a 5.9l cuummins mated with an at545. Doesnt go anywhere quick but I get here.

Lately Ive been noticing a cooling problem.

When I first start the engine from cold and then go for a drive, the engine temp creeps slowly all the way to 240. The fan clutch engages at 220 but the temp keeps building to an uncomfortably hot temp.

This is all experienced on flat roads btw and average outdoor temperatures, no grade or hot days. I let off the gas to bring down rpm and itll slowly come back down to 210.

Once this has happened, I can drive it with no further issues for long stretches with no overheating experienced again.

Why is this happening? I dont like seeing it get up to 240 degrees as Ive had the check engine light come on a couple of time when it gets that hot.

Steps Ive taken to try to solve this:

1. Taken the cold weather louvres off the intercooler to allow more airflow.
2. Flushed the radiator and new coolant put in.
3. Installed new engine temp sensor and new engine temp gauge (To ensure accurate temp readings).
4. Removed the interior heating plumbing to the rear heaters.

Im leaning towards an issue with t t-stat maybe? Anyone experience this as well? Any way to add additional cooling?

 

[mtnfreak]

Have you replaced the thermostat?
I did mine and solved my overheating issue on 8.3 cummins.

 

[-cycosis-]

Nah thats what I think Im going to replace next. I wonder if its sticking in the closed when the block is cold and gets forced open by the excess heat?

 

[nikitis]

Thermostats sometimes go bad and won't pop.


If you've checked the coolant levels and looks good, this is a good next step.


If that fails could be a bad water pump.

 

[mtnfreak]

Not sure but our bus is a 2000 bluebird and overheating was slight inclines, hot days, would get up to 220 then I would need to shift down and crawl up hills…when i pulled the TS out it looked ok but I think might have been the original. Someone told me they need replacement every few years. Use an OEM one the others can be iffy.

 

[Albatross]

This sounds exactly like a thermostat issue.


A thermostat uses different kinds of metal to force a valve open to allow new coolant in to the block. When first started, even with your water pump running, the engine block will keep the same coolant in it until the engine gets up to temperature. Once that temperature is reached, the thermostat opens, and colder coolant is allowed to enter the engine block. Eventually, all the fluid in the system should be at more or less the same temperature, with the coolant in the block being heated up, and then flowing back to the radiator to cool off, and then back around the ring again.


The problem you're describing is because your thermostat is "sticky" for some reason. It could be gunk, it could be old, it could be the spring around the seal... Who knows, who cares, the problem is definitely the thermostat.


You can spend an extra dollar or two (maybe three these days) and buy a "fail-open" thermostat to install at the top of the water-jacket for your block. When these thermostats fail, they fail in such a way as to not impede water flow; this is a superior option when you're living in basically any place where winters are shorter than six months. It may take longer to heat up, but it will still work. And for me, personally, growing up in Texas, I've had a few vehicles where I simply pulled the thermostat out completely, as "running too cold" was something that could never really happen, even on a diesel.

 

[cadillackid]

+1 on sounds like a thermostat issue.. its probably opening partially but not fully.. then when you get it really hot, the spring pressure is high enough to pop it open the rest of the way where it stays till you cool the engine down again..

 

[s2mikon]

A number of years (decades) ago I had a service truck with a Cat 3208 engine in it, and when you put it under a load (think ridge route I-5) it would begin heating up past 220 and I would back out of it and it would cool down to 210 and then when I kicked it in the butt again it would stay at 210 the rest of the way to the top. This happened a few times so I went to Cat and bought 2 new t-stats, Cat used 2 in the housing. Worked fine after that. Later when I had some time on my hands I put a pan of water on a heat plate and placed a feeler gauge in each t-stat and suspended them in the water. When the water was at about 180 one t-stat fell to the bottom but the other one hung on until the water was beginning to boil at that point it fell off. I like the idea of 2 t-stats to give you a little bit of safety margin. Don’t buy anything but genuine OEM. The aftermarket stuff is junk as far as I am concerned.

 

[cadillackid]

A number of years (decades) ago I had a service truck with a Cat 3208 engine in it, and when you put it under a load (think ridge route I-5) it would begin heating up past 220 and I would back out of it and it would cool down to 210 and then when I kicked it in the butt again it would stay at 210 the rest of the way to the top. This happened a few times so I went to Cat and bought 2 new t-stats, Cat used 2 in the housing. Worked fine after that. Later when I had some time on my hands I put a pan of water on a heat plate and placed a feeler gauge in each t-stat and suspended them in the water. When the water was at about 180 one t-stat fell to the bottom but the other one hung on until the water was beginning to boil at that point it fell off. I like the idea of 2 t-stats to give you a little bit of safety margin. Don’t buy anything but genuine OEM. The aftermarket stuff is junk as far as I am concerned.

even the OEM... I changed from a 195 to a 180 in my T444E (the earlier T444E got the 180.. the later got the 195).... it was right from the IH dealer.. it worked great the FIRST time.. opend right up at about 175-180... never closed again

 

[-cycosis-]

This has all been immensely helpful.

Ive reached out to my bluebird dealer who is my mechanic and they are chatting with their techs who serviced my cooling system. Likely gonna request a new t stat asap.

 

[sportyrick]

OEM ONLY, all others are imposters!