My truck currently has the original, unrebuilt 302 in it. It's a 79 f-150. It has 150,000 miles. I am pretty sure the thermostat is stuck open as it has always ran on the high side of "normal" on the temp gage when running at highway speeds. Now at highway speeds it runs on the bar for the very end of normal range, hotter than it used to. I had the truck on a lift to find a rattle and found the muffler was going bad so my buddy put a 5.9 Dokata R/T muffler on it (free flowing, not loud, a new take off and free lol) and got rid of the cat. The cat was very stopped up, to the point the muffler guy didn't know how I got there. We figured that had been causing my hot running problem. But the temp has not changed, althought I have alot better performance.
I put a new radiator in last year along with a new heatercore. I was going to replace the thermostat but that requires removing the water pump and timing chain cover. If I do that I might as well replace the water pump and timing chain, which I'd rather not do as I will be putting a new engine in in a few months. I'm just trying to get it to run cooler for the time being. It only does this at highway speeds (55 plus) and if I slow down to 35-40 the temp goes down. Any ideas of whats caused this? It's started running hotter in the last few months, but the thermostat has been stuck open the entire time I've owned it. I'd like to just get it running alittler cooler so I'm not having to constantly watch the temp gage and fear overheating (it's never boiled over, I also have an over flow tank and the truck is always full of water and oil as it should be).
Please advise.
Nick

 

Chaning the thermostat does not require removing anything but the upper hose and some anitfreeze. There are 2 bolts in the intake that are a pain to get in and out. I have on mine took off the dist cap and/or turn the dist to reach the lower bolt though.

 

If your thermostat was stuck open the truck would run cold, even colder on the interstate. stuck closed, it would overheat and keep going up until you shut the engine off (or locked it up). thermostat may be part of the issue but not all of it i dont think...
do you have a sufficient fan shroud mounted on the radiator? i think the thermostat is probably working, maybe not well, but enough that its not overheating. its definately not stuck open or closed.
a fan shroud makes a huge difference if you dont have one, if you do....then i would go ahead and flush the system a few times and replace the thermostat and see what it does. be sure to use distilled water to mix with the antifreeze...well water and even city water has deposits that corrode the inside of the engine and also usually are what cause thermostats to go bad. I even put in about 1 cup of machinist's cutting oil to coat all the metal and reduce corrosion, just for added protection.

Jimmy

 

The engine being a 302 requires me to remove the water pump, along with the A/C compressor bracket to get to one of the bolts (atleast on my truck, does yours have A/C). I have not tried the distributor,hadn't thought of that.
It has the factory fan shroud on the radiator. The engine/engine compartment is as it came from the factory minus the smog pump.

A thermostat that is stuck open will cause an engine to run hot at highway speeds due to the fact that it is being cooled enough by air flow (esp. in the cooler times of the year) and because the air is moving too fast over the radiator it will not sufficiently cool the "water" and the engine will continue to get hot (to a certain point, not over heating though). Most thermostats will close after you have been on the interstate for awhile. This engine takes quite sometime to heat up, longer than it should, but once your on the highway for a bit the temp gage continues to climb until the top of normal. Atleast that's been my experiance, there have been several "tech letters" published in Hot Rod, Car Craft, etc through the years on the topic. I agree with you and I'm sure there is also another problem as the thermostat has been stuck open since I have owned the truck and it just recently (past few months) starter getting hotter than it normally does. I've picked my brain and can't think of anything that would be causing it to run hotter (other than the cat, but that was removed and it hasn't affect the temp at all). Hoping someone knows something I don't
Thank you guys for your help!
Nick

 

Mine is a 79 F-150 302 with AC also and I never had to remove anything but what I said before. The lower right bolt is a real pain which is made easier my moving the dist(mark where it was before moving). Yours could be different from mine but I have had this one since it was brand new in 79. Good luck in fixing whatever is wrong though! I had to replace the radiator about 10 years ago when it started to run hotter and hotter but you have already done this.

 

Usually getting hot at high speeds means that some of the flaps and baffles are missing that direct air thru the radiator at high speed (>35). The air flow produced by the vehicle in motion takes the path of least resistance and bypasses the radiator.

A lean condition or EGR systems can sometimes contribute to the problem.

 

I am missing the flaps that go in the middle of the core support (the ones on the ends are still there). I assume one goes here as there are holes for it. I'm sure I can get the plastic clips that push into the holes, but where could I get the rubber type flaps that go here? Could I use say a tire inner tube cut to fit?

Last I checked the EGR was fine BUT you never know. This truck doesn't really have any off the line power due to 2.75 gears and 150,000 miles so I dunno if I would beable to tell a loss of "power" off the line (not sure if the EGR on this truck would do this but on chevy products I've worked on you can tell a noticeable differance after the EGR was replaced.)
Whats a quick/easy way to check the EGR? If I remember right I can take the vacum line off and plug it with a bolt, if the engine has more "power" the EGR is bad, correct?

Custom79- I appreciate the help and I'd like to apologize because I think my reply came across as rude. Didn't mean for it to sound that way but it did. Sorry bud and thank you for the help!

Nick

 

I use rubber belting like is used for conveyors for replacement flaps. You can get it from rubber supply companies, often as scrap. You can also use Kydex brand plastic on some of them. Kydex is an ABS plastic sheet available from plastic supply houses.

You can plug your EGR vacuum line but you really need to determine if the valve is leaking. You can get more information in the engine forums.

 

No problem.....I just hope you get her fixed.

 

I got to looking at it yesterday and I think I'll make some of those "flaps" out of metal. All that'd be needed is use a metal brake to bend the the metal at the top and bottom. Think it'll work?
Nick