running hot

[blackdog1]

I've got a 79 Chevy K30 srw, 400 sb turbo 350. I can't drive anywhere with out running the temp up to dangerous levels. I've been told that the 400 2 bolt siamesed is especially sensitive to heat. I run with the plow just a few inches off the ground and things are ok until I have to get on it:burnout . When the blade is down plowing the temp is fine. I have to transport the plow some pretty good distances and this is starting to p** me off.Any help would be appreciated. How bout fitting a 6.2 diesel radiator in there?Electric fan? Thermostat? Thanks:headwall

[wyldman]

A thermostat will not help your overheating problem,unless it's stuck closed.It determines how cold an engine runs,not how hot.If it's been in there a while,it wouldn't hurt to change it to make sure it's not sticking partially closed.

Check the belts,and make sure they aren't slipping.

Check the rad,and make sure it's in good shape,and not plugged internally.It's hard to tell sometimes,and you may need to pull it out and have it cleaned out.Another option is to upgrade to a larger 3 or 4 core rad.It will help by adding more cooling.

Check the clutch fan.The plow may be disturbing airflow,and not allowing the clutch fan to heat up enough to kick in.Replacing it with a solid fan for the winter will help.

Also check the AC condensor (if equipped with AC).It may be plugged with debris,or the fins may be bent enough to restrict airflow.

The last thing is to make sure you have a large external trans cooler.It will help cool things down,and prevent large amounts of heat from the trans fluid to overwhelm the cooling system.

[John DiMartino]

The only things i can add that wyldman didnt already cover was the clutch fan,and shroud.I know that the thermal type is the one you want some cheaper clutch fans work off speed only and disengage above a certain RPM.You want to make sure yours has a spring in the front of it,and it works.Also if the radiator is transferring the heat like its supposed to be a good clutch fan should lock solid about 220-240 degrees,and start to drop the temp down real fast.you should hear the roar as it kicks in,and it will actually slow the truck a bit,since it takes a lot of HP to turn it. Once temps come down it shoud disengage and freewheel again.The one other thing is make sure the rad fins or condensor of it has one,isnt plugged with dirt,bugs,or road debris.A bit if compresssed air or a good degreaser/light power washing sometimes will do the trick if its not too bad.Sometimes you cant even see thru them with a flashlight in the other side they are so plugged up with debris.Check that good if you havent already. Finally i notice a lot of older trucks over the years tend to lose there shrouds,either from breaking them,or not being re installed after engine work. You need a fan shroud if you dont have one,sometimes non tow pkg trucks come with a top shroud /guard only,if you can get your hands on a full shroud it will help tremendously with cooling esp with the plow blocking the radiator.
My personal guess is with wyldmans,the rad is internally full of corrosion and the tubes are likely plugged if its been in there more than 5-6 yrs or so,and the coolant hasnt been flushed regularly. For what new rads cost if there is any doubt id just get a new one,and the biggest you can fit in there.

[79D604SPD]

My 79 K20 with a 400sb had the same problem with intermittently running hot and turns out my radiator fins were plugged with dirt and dust and everything else. I cleaned them out and now it runs around 195-200 degrees. My AC didn't work anyway, so I removed the condenser. My radiator is the factory 4 core.