overheating/thermostat issues

[jaynes]

It's starting to not be an issue, as the temps are falling here in Mid Mo. , but when it gets warm, so does the engine. Going about 75-80 mph on the highway for an extended period of time at about 80 degrees or more, the engine will start to over heat... the thermo gauge just keeps climbing and climbing, until I have to slow down to 70 or under to keep the temps down! This is very annoying, also when it gots hot, the idle rpms drop drastically. After I've been running on the highway for an hour and it's warm out, I have to keep my foot lightly on the go pedal to keep the rpms up, other wise the idle drops so low the press. light comes on, and it feels like it could stall. This certainly isn't normal, and the idle is set fine, and idles fine when it's cool. This stuff is only when it gets hot. Any suggestions, like thermostat, radiator problems, anything else?? Thanks, sorry for the length!



jaynes

 

[y-knot]

J, Several years back I had a sticking thermostat that would stick closed till the temps got to 190 or so then open allowing the temp to drop like a rock. it would continue to do this cycle over and over, sometimes with a break where it would read normal, and then right back to the crazy up and down routine. I replaced the thermostat with a new one and it solved the problem. I remember Cummins passing out new thermostats at the Indy Cummins 200 race in '98 I believe, they had a batch of bad ones go Thur the plant.

 

[tugboatphil]

Jaynes,



I had my water pump go on the 90. Prior to failure it started "weeping" antifreeze out a small hole on the pump. This is apparently an indicator. However, I don't recall having the same overheating problem as you describe.

 

[bgilbert]

Jaynes, I'm in the same boat as you. My 91 727 tops out at 80mph, and when I run 75-80 for a period of time, it will run hot almost with the gauge all the way to the HOT side. This is empty, so I'd hate to see what pulling a load in hills would do. I just figured its a Cummins and it will run wide open all day, but I kept thinking something would let go. SO I am gonna buy a new updated thermostat to see if that cures this problem. All my cooling items are in good shape, I just don't know about the t-stat. I too would like to hear more thoughts on this.

 

[jaynes]

I'm relieved, although not excited, to hear I'm not the only one with a problem like this. But does your idle drop really low when it gets that hot? Why would it do that?



jaynes

 

[Bob Beauchaine]

If you've got the drop down radiator (tubes running verticle) they could be a problem. I've been a Dodge man for 40+ years and they could not build a cooling system that works well - still can't. My '93 has a cross flow radiator and I can run all day with my AC on towing my trailer in 95 degree weather at 70mph. My temp stays at 180 without any problem.



There are posts in the archives about converting your truck to the crossflow radiator. Also make sure your fan is working properly. It should produce a noticeable increase in noise when it comes on at higher temps.



Bob

 

[DBF]

cross flow radiator

Bob, can you remember the company that made this cross-flow radiator and the model number? I'm coming up on time to replace mine.



Tx, DBF

 

[JLEONARD]

I must be lucky, and I hope I don't jinx myself, but mine runs at the same temp all the time once it warms up.

The gage reading varies about 1 needle width from running the city streets, to running at 75/80 for an hour or more.

I normally run empty, but I have had a small load occasionally and it doesn't affect it at all.

At idle it might cool by an extra needle width... but that's about it.

That's summer and winter without a winter cover in the grill.

Jay

 

[bgilbert]

J, I think it has something to do with the non-OD transmission running the engine wide open for periods of time. My 89 5 speed has never run hot. 2600 rpm -don't know for sure, just guessing no tach equates to 80mph on my 91 727, 80mph on my 89 5 sp equates to about 2000 give or take can't remember the 89's been sitting for awhile.

 

[JLEONARD]

Bill,

OK. That makes sense.

At 70 I'm at about 2000 rpm... . at 80 about 2200. That's with 3. 54 diff ratio.

Jay

 

[michigandon]

If any of you guys want to convert from a downflow to a crossflow radiator, I still have a '93 rad out behind my garage. It will need to be recored (got trashed when the donor truck was wrecked), but the side tanks appear to still be good. It's free to anyone who wants to either come pick it up or pay to have it shipped to them. Or I can bring it down to Peru with me this weekend, although I realize that's kind of short notice.



Based on my own experience thus far, I righly recommend an aluminum radiator. I realize that that may not fit into everyones budget though.



Don