1988 3.0 gets pretty warm on grades on the highway. Needle goes to around 3/4 of the way up when climbing long steep grades (especially in warm weather). I’ve pulled real steep grades in 30-40 deg temps and my gauge do much. Anyways, as soon as I flatten out or go back downhill, the guage will drop back down to around the 1/4 mark. On a fairly flat stretch at around 65 mph it will stay around 1/3-1/2 mark which is normal operating temp I assume (only toyota Ive owned). When driving around town and on trails it stays at the 1/4 mark. It’s never gotten up to the red caution area on my cluster. After these heating episodes grades I’ll notice the reservoir gets drained to almost empty.

Backstory: When I first got the truck I replaced the thermostat and main coolant hoses with all OEM parts and purchased a new csf radiator and cap. Truck had slipped a timing belt shortly after and I ended up just dropping a new engine in (0 miles). Out of curiosity I opened up the original engine since the coolant I had drained out when I got it was nasty. As expected, the coolant passages were awful. Brown sludge and completely blocked.

Been putting this off for way too long now. From what I’ve read, the best route is pressure testing the coolant system and flush it. Im hoping junk from the original motor didnt get into the new radiator and clog it. Is there anything else I’m missing that would be causing these issues?

 

Double posted for some reason. Not sure how to delete the duplicate.

 

I think you are on the right track. The engine and transmission are working harder uphill and the necessary circulation maybe just isnt there. Definitely flush. Helps to flush it from the heater hoses too.

Coolant can evaporate or burn off over time. How much are you losing? Wouldnt hurt to double check your work for leaks too. Could be slowly introducing air into the system causing the overheating too. Pressure testing will help you track down a hose leak very quickly.

 

Update: its my fan clutch. I can stop it by barely putting my thumb against it. Unless this is normal with this truck which i would find odd.

 

Depends on the temp. Stopping a fan blade when it’s not hot on the gauge is fine. If your gauge read 3/4 hot and you could stop with your finger that would be bad