Odd...Coolant temp fluxuation

[dengerin]

'76 with a stock 2F

So at a stop/idle, my coolant temp rises rapidly, into the 'H' on the temp guage, but not enough for steam and all the goods to rush out of the radiator. Then, as I gain speed/RPM on the engine, coolant temp drops to just below the 'C' on the temp guage. Then, push in the clutch and roll to a stop, and the coolant temp shoots back up, usually before I have rolled to a stop.

What do y'all think? Do I just need a flush and fill, or is there something bigger going on. I've never experienced this before.

Thanks in advance.

 

[Poser]

Welcome.




Are you running a fan clutch?

What is the condition of this?


If when the engine is cold, have you tried to spin the fan by hand, with the engine not running?


If the fan spins freely when the engine is cold, then your fan clutch is junk.


Have you noticed a drop in coolant level at any time in the last month or so?


Have you got the engine HOT for an extended period of time?


Is your oil clear or at least black and not milky brown?

 

[Tunnelratt]

First of all check " SEARCH" there have been many posts on this, secondly run down the list of what have I done's, did you open the system and drain it down then forget to" Burp" the system, if you didnt " Burp " it can leave an air pocket in the head and give you fits, check the gauge, the factory one is prone to failure and incorrect readings, get one of those Air Conditioning thermometers with the long probe and the round dial on the end,slip it between the fins on your radiator, run the truck in the front yard and get it up to operating temp and watch the needle, it will heat up, when the thermostat opens the temp will drop, when it closes the temp will rise, hows the radiator? old, plugged up etc, water pump? thermostat, hoses, water passages clear? timing set correctly, whatever you do do something, I run a 75, 40 with a 76 engine, I blew the head gasket, and thinking back mine gave me similar warnings before it blew, I've since replaced every component on the cooling system and life is wonderful, also run an after market guage and an 8 blade factory fan

 

[dengerin]

Well... seems to have been related to an earlier idle adjustment/vacum leak issue ( https://forum.ih8mud.com/showthread.php?t=99757 )

Leaks fixed and carb adjusted all nice and pretty, and bam...no more coolant temp changes.

Guess I should fix one problem at a time.