I recently put 33x10.5 bfg mts on my 1982 p/u. I did not do anything to the gearing.

I tend to drive my trunk in the city 90% of the time. It is now hunting season so I have to drive about 60-90 miles freeway to get to my spots. I noticed that I was overheating I got the needle touching the line and then I managed to downshift to 3rd but reving the engine really high to keep up with highway speeds and it managed to cool down a little bit (about 85% to 99%) I had to keep switching gears from 3rd to 4th I could not just keep it in one gear or the truck would overheat. I have a L45 4 speed transmission ... I am just curious if the upgrade to bigger tires is causing this, or where should I start trouble shooting?

 

The tires would put a bigger load on the engine, but the cooling system will work just as good if it is in good shape. This might seem obvious, but make sure that there is enough coolant in it first. If you do any wheeling, check that the radiator is not caked with mud or anything like that. Do you ever hear the fan come on while driving? If not, then the fan clutch might not be working properly. My fan clutch quit working a while back and the temperature would only climb when I put a large load on the engine. Downshifting to 3rd cools it a little for lots of reasons. I did the same thing before I changed my fan clutch.

 

I was going to start with a thermostat that seamed the most reasonable. I also had thought about the fan clutch ...that changing gears must have put different torque on the clutch and caused it to spin a little

is there a real way of testing if it is the fan clutch?

 

Yeah there us I dont quit remember is has to do with truning by hand I dont remember I am planing on putting a electirc fan anyways on mine, thats the way to go, one less pulley. I know for sure it tool me a while from over heating everything from thermostat to new radiator. I now have new everything and the sucker wont over heat at all. Sometimes while your going down road you can tirn on your heater to help also cool the engine, it disipates heat from the engine. Fuel mixture can also do it to, see if you are running rich, getting the right fuel mixture can cool your engine especially at idle. Let me know man what happens

 

If the fan clutch is working then the fan will come on when the engine starts to get hot. You will hear it. Thermostats usually get stuck closed, but there is always a chance that it got stuck partially open. It is easy enough to check, so it would not hurt to do so. If it is old, then you might want to change it anyway.

 

did the thermostat no change....
then I did a new fan clutch and bingo nice temps again

 

well damn .. I drove it Sunday morning for a hunting trip 100 miles going 65 the whole way and it worked fine. On the way back I got within 10 miles of home and my temps jumped in the red and I had no heat from the heater. So I called a buddy and we put in a new thermostat and that was a no go.. I am at a loss really ...at this point it could only be a bad radiator(blockage) or a bad water pump.

or am I missing something? ...how can I check if the radiator is bad or the water pump is bad?

 

You can check the radiator for cold spots by warming up the engine and carefully checking for cool spots. If some passages are clogged they won't be as hot (tip: get a non-contact thermometer which instantly reads the temp). Water pump is a possibility as well since you have no heat, perhaps nothing is circulating.

 

Could be waterpump if revving the engine helped keep it cooler or it may be the radiator, as mentioned that was unable to shed the additional heat of the larger tires. Often you can look inside the radiator at the cooling passages to look for deposits. Best place to see is the lower hose connection (radiator drained of course).

 

What if the alternator belt was lose?

 

The alternator belt being loose might have an effect on it. It would have to be really loose though, and it would probably be squealing. Did the driving conditions change when it overheated? Like a steep hill or stop and go traffic or something like that?

 

Steep hill this last time now it happens on flat ground...and I took it out wheeling right before all the problems started went through some big water puddle crossings and the belt started squeling ..although after it dried out it stopped slipping...

[update]

I am loosing a lot of fluid ...and my exhaust has a lot of white smoke /condinsation ...headgasket time ...well at least now is a good time to do that 22r/20r hybrid