i recently picked up a '79 bronco. I thought it was running a little warm. On the "A" in normal on the gauge. When i went to replace the thermostat, there was quite a bit of pressure on the blockside of the therm. is this normaL? i also noticed no fan shroud so i will get that replaced ASAP as i am sure it is causing alot of the problem. But the block coolant pressure concerns me a little. Any ideas??

Thanks
AO

 

Not sure what you mean by a lot of pressure on the block side. Do you mean the thermostat spring pressure was high or did water shoot out from the housing when you removed the hose? Or do you actually have a pressure gauge on the block?

A TStat will have a pretty strong spring. You can test a TStat by putting it in a pan of water with a thermometer and bringing it to a boil. it should open when you reach the operating temp.

On a truck as old as yous, I might suspect scaling inside the block and or radiator. You will need to chemical flush the system and might even need to rod out the radiator core. You might also just have an old inaccurate gauge.

Good Luck,

Jim Henderson

 

Jim- some fluid came from the hose but not much. I dont have a gauge on there but when i pulled the tstat out of the port , i had a small geyser. Just was not sure if that was normal

thanks

 

Water flowing out the TStat housing can be normal. It all depends on how low the housing is relative to the highest water level in the cooling system. Some overflow tanks are pressurized(probably not a 79 tho) and above the TStat housing which can cause water to gusher/geyser out maybe 3-4 inches for a few seconds.

Most cooling systems have relatively equal pressure in all parts since the block and pump only have one vavle, the TStat, so once the pump shuts off and the TStat is closed, the pressure should equalize on both sides of the TStat. If there is a lot of scaling in the block or radiator you might get a pressure differential but the time it takes to remove the housing should be enough for the pressure to equalize.

So my guess is that there are water pockets or tanks higher than your TStat housing which would cause water to gush out when you first remove it. I wouldn't worry about it unless it was shooting out say a foot above the housing, everythting is relative.

I think getting a new shroud will dramatically improve the temperature reading. If it did not improve I would look at gauge/sender problems and then radiator core and block clogging. I had a car that had a bad gauge and it always read very hot even though a regular thermometer in the radiator tank showed normal temps. I also had an engine with 180K miles on it that even though it was well maintained, it got deposits in the core from the antifreeze and additives used.

Good Luck,

Jim Henderson

 

thanks for the info jim. very helpful. I am picking up a shroud today and will go from there.