Coolant temp fluctuations

[showknow]

'91 4.0 4x4 Auto 170k

Had overheating probs this summer in FL. Told it was the fan clutch.

Back in NC since March. Overheated in stop and go traffic but was good temp at high speed. So I pulled the therm at that time, not much money to spend.

Recently, replaced fan clutch and therm. Rad is two years old. Pump is two years old. Flushed system. Replaced top and bottom hoses. Temp gauge moves from N on NORMAL up to M and the cools right back down in cycles... I could set my watch to it. No matter the speed I'm going or stop and go traffic.

Any ideas?

 

[ricco750]

'91 4.0 4x4 Auto 170k

Had overheating probs this summer in FL. Told it was the fan clutch.

Back in NC since March. Overheated in stop and go traffic but was good temp at high speed. So I pulled the therm at that time, not much money to spend.

Recently, replaced fan clutch and therm. Rad is two years old. Pump is two years old. Flushed system. Replaced top and bottom hoses. Temp gauge moves from N on NORMAL up to M and the cools right back down in cycles... I could set my watch to it. No matter the speed I'm going or stop and go traffic.

Any ideas?

First, you're a brave man to show your pic...occasionally we get some real psychos on this site, although most folks seem to be nice.

Anyway, to answer your question, I'm the original owner of my 93XLT 4X2 with 245,000 miles on it and my temp gauge has done this the whole time...and I've been through three rads, four fan clutches and fans, four therms...you get the picture. That being said, I did something this past weekend that I have never done before...I needed a new water pump (#4), so I went through the whole system. Everything got replaced, even the heater core, with the exception of the radiator, which was in good shape. But here's what I never did before...I replaced the temp sending units on the water pump housing...one goes to the dash, the other goes to the computer...and now my dash gauge sits very steadily at the "N", with a slight move up into the "O", then back down. I'm not running a fan clutch now, as it's quite cold. I'm gonna go electric in the Spring. My two cents.

 

[alphamale]

Temp

Howdy, my 93 ran like that for a year after replacing my head gaskets. While the engine is running pull the upper radiator hose at the radiator and see what kind of flow you have. Make sure you are putting water in the radiator so as not to let the engine run out. I had one heck of an air pocket in the cooling system. By pulling the top hose you will be able to tell if their is air in the system. Also with the radiator cap off allow the engine to warm up. If water is blowing out the radiator opening could be blown headgaskets or just air in the system. I took my water pump off and ran my garden hose into each water passage until almost all the air came out of the block. Preatty much resolved that issue. One thing they should have done on these engines was to put a shrader valve or bleed valve in the system to bleed the air out.
Hope this helps.