Truck Overheats only in 4wd


Hello! I have a 74 chevy Silverado c-10 with a 350.It was overheating, so I put a new Thermostat in.I live in the mountains and go up VERY steep hills everyday.It only seems to overheat in 4wd.I have an hour commute to work through the mountains and it is fine.I dunno what the deal is.Any clues?Thanks


Only SEEMS to overheat in 4 wheel drive. In 4hi?

Is the tranny ‘hunting’?

What kind of road/surface is this? Gravel?


speed when overheat occurs?


I’m guessing that you only have it in 4wd to crawl up the steepest hills, in which case having the 4wd on and the overheating are both the results of the steep hill. When you’re crawling up a hill, your engine is working very hard and there is not very much airflow through the radiator. If your cooling system is borderline, this may be the only time the trouble shows up. I’d pay particular attention to the fan clutch (if it has one) and make sure the cooling fan is getting full power. A partially clogged radiator or a waterpump on the way out could cause this too.

It is also entirely possible that the cooling system is working just fine, but isn’t adequate for a steep long-distance climb in 4wd. The four-wheel drive does add a bit more drag on the engine, as does an automatic transmission, if so equipped. You may consider a more effective radiator, a transmission cooler and/or an aftermarket, possibly electric, fan.

Also, I think what roadrunner may be hinting at is that if you’re using 4wd on a surface that doesn’t have enough “give” , it can be extra-hard on the drive train, as well as causing long-term damage to the transfer case.


If you aren’t driving on dirt or crushed stone, you shouldn’t use 4WD. Check the radiator from behind. If you see white or green coloring anywhere, you might need a new one. If you see missing fins between the tubes, replace the radiator. If the radiator is over 12 years old, replace it. Have the ignition timing checked.


It is a gravel/dirt road. It is an automatic. I have been goin in 4lo. after you said fan clutch it made me think… I dont have a fan shroud. Do you think that that could affect it.? Thanks


A shroud is definitely needed to couple the fan to the radiator and flow air properly through the radiator. The problem will become more pronounced as the radiator begins to build up scale internally and doesn’t cool as effectively. Before you mess with the fan clutch, get the correct shroud installed.


Nope. I’m looking at a heavier load on the engine.


Ahh, good. This answers my question too. Hope the shroud does it for you.