Hey everyone, so I've finally got my truck ('70 F250 w/ a 390) up and running last week. It's first trip I took it around the block then at the end of the day a longer trip. After an hour and a half drive on combined freeway and streets but mostly freeway, ran great no problems. Tonight I took it home which is mostly freeway and halfway the temp gauge started to swing to the hot side. I pulled off the freeway peeked under the hood and the gauge settled and the radiator was full to the brim with coolant. Touched the lower and upper hoses and they both didn't seem too hot. Hop back on the freeway and I noticed it started to swing over to the hot side again anytime I let it coast or I wasn't in the gas pedal. What is going on?? Any ideas or is this just some screwed up coolant temp sensor? Please help.

 

Hi, I'm not a mechanic BUT my first thought would be to check or change your Thermostat and if that doesn't fix the problem, then maybe your water Pump is not functioning at 100%. Probably not getting that coolant fast enough into your motor. GOOD LUCK !!!

 

With a new build, one can't say everything is working fine until.... Don't know where you are but the temps are generally down in the US, so hot weather shouldn't be on the list. The thermostat and the sending unit is where I'd start. Could possibly have some air in the block somewhere.

Our trucks have big radiators with no built in overflow so you need a couple inches of air in the top for expansion. Don't keep refilling it to the neck if you find it down. Do you know aprox how much coolant was used in the first fill?

Should be more of a minor issue.


John

 

I would not trust the OEM gauges. They are notoriously inaccurate.

With radiator cap off, run the truck until the thermostat opens (feel upper hose), when hot fill with coolant/water until nearly full and watch for circulation in the radiator.

That will ensure you don't have any air bubbles and you are effectively "burping" the system.

 

3X on the thermostat. Besides it probably being the problem make sure you have a quality one in there. No China crap. And I don't mean to insult you but, make sure thermostat is installed with the spring side down towards the hot coolant in the engine. NOT pointing up at the thermostat housing.

 

After I rebuilt my engine it ran hotter than I liked, so I changed out the 195 degree thermostat for a 160 degree stat. After that it ran just where I wanted it. If you have a 195, you could try a 160 or a 180, if your engine actually is running too hot.

 

Yep fresh rebuilds all run warmer for a 1000 miles or so. A lot of guy install a aftermarket recover tank, then you can fill the rad all the way full. You also use a different rad cap for the sealed cooling system. Yeah if your worried put in a 180* stat

A 160* is a little on the low side as engine run at their best when warmer. Plus running cool air into them helps too.

orich

 

I AGREE, if you do change the Thermostat make sure you ask and get a QUALITY one not a CHEAP one. I made that mistake on my 1958 F250 and I ended up having to take out the Cheap one and went back to the auto parts store and they found a Quality one for me. 1 Year now and no Problems, GOOD ADVICE "JEFFFAFA"

 

Don't forget to drill a 1/8-inch hole on the thermostat flange to allow air to bypass or else air will be trapped on the engine side of the T-stat. When installing, the hole should be at the 12 o'clock position. Dig?

Also, open the heater control valve to cycle out any air trapped in there after working on the cooling system.

 

did you bleed the air out of the heater hoses ? Might be a simple air blockage and that the radiator is not full . Another problem could be simply installing thermostat backwards ?

 

You got that backwards there bud.......

 

Yeah, the T-Stat in these pictures is installed backwards.

 

Uh, no it isn't........

 

I knew you would come up with something comical there Area. I'm just waiting to hear what Hio's gonna say!

 

Tis back assward all right!!. The spring goes into the manifold..
orich