Hi everyone, I have 1993 F250 7.5 and I’m having an issue where the coolant temperature is fluctuating. Recently, my thermostat was leaking so I put a new thermostat gasket inside and it still leaked I ended up using Permatax gasket maker for thermostats and water pumps. It fixed the leak and before the truck was sitting for three months, but never had an issue with any cooling related things. I proceeded to bleed air in the system by opening the radiator cap having the heater on full blast and filling up the radiator as the coolant level went down. I then took it on a test drive today and I noticed that the coolant temperature was dropped below normal when I was driving, but then go a bit higher than normal when Idling. thinking there still might be air in the system, I tried to purge the system again by opening the radiator cap and letting it sit. As I was waiting, I pushed the gas a little bit for a few seconds, and then let go then suddenly a burst of coolant shot straight up in the air and I had shut the car off. After that, I began to fill the coolant again as it was low on the radiator. It seem to have taken the air out, but the temperature gauge was still acting funny as it was above normal temperature while idling. the coolant level on the radiator was going up and down a bit and when I shut off the car again, coolant was spewing out from the coolant auxiliary tank. While this was happening, I could hear what seems to be air like bubble noises coming from the radiator and the hoses. does this mean that I still have air in the system or maybe even a faulty thermostat? I shut the car off before the temperature gauge went to the red so I’m hoping I didn’t overheat the engine. Thanks for those who help with this matter in advance. This really isn’t a New Year’s that I had in mind...

 

Find a steep embankment and drive the front end of the truck up it. The goal is to the the front end as high as you can and let it sit there for a minute idling. Freeway overpass embankments are pretty handy for this since they're usually paved so even 2wd trucks can crawl up them.

 

I do have a pair or ramps that i can use to have the front end up that i use for oil changes on my other cars. would this be enough and could really something this minor cause the symptoms i've described above? last time i did the thermostat and bled the system, it was on level ground. not to mention i drive maybe like 500 miles or so a year max so im not sure if my thermostat would fail...

 

Ford v8s are usually self bleeding. The biggest problem I've run into is that the heater core will trap air and not put out heat.
I've only had to do my trick in a handful of vehicles, usually sedans. But it's worth a shot to see if it helps. It's free.

 

I’ll give that a shot. When I test drove the truck, the heat worked fine so it’s gotta be the air in the system or maybe something wrong with the thermostat and/or radiator cap. I did order them just in case but it does make me wonder if the thermostat is defective or maybe a piece of permeated is making it malfunction…

 

3 ways to verify T-stat.

Cheap IR gun monitoring output side of housing/hose from cold start.

Drill T-stat housing for temp sensor on output side of housing. ( I have Autometer manual gauge)

Pre install of T-stat test with controlled temp increase in pan of water & hi-temp/candy thermometer to verify opening temp. (something I always do.)

It helps to always use a Motorcraft t-stat too.

 

Have you replaced the radiator cap?
I've been in the habit lately to replace the rad cap at the same time I replace the thermostat.

 

I’ll try to use the thermo gun I have next time. I’ll also have to look into the housing temp gauge also.

 

I actually ordered a new thermostat and radiator cap. It’s been maybe 4 years or so since I’ve replaced them but I only drive around 500 miles a year or so. Nonetheless, it’s really to have something like what I described happen when all I did was replace the thermostat gasket…

 

When I replace thermostats I always drill an 1/8" hole in it and the system always bleeds itself.

 

Did the thermostat come out, and not installed backwards?

 

I never knew or heard of that method before. does it work well and how does it work?

 

I believe I did install it correctly. I have health issues that causes short term memory so i would have to double check. I even bought a new thermostat and a new tube or Permatex waterpump/thermostat gasket maker. Its been getting harder day by day to do things...

 

Motorcraft units have it from the factory

(Edit, got the wrong quote.... )

 

Been using that method on Mopars for 20 years now. Haven't had to burp a coolant system since. Did the same this past winter when I replaced the thermostat and radiator in my 4.9L.