Hey all,

So several months ago I got my 79 F250 4x4 300 Inline six rebuilt and back on the road. It runs great but with the rebuild I upgraded the carb, intake, exhaust and cam. Edelbrock 500 carb, Offy intake, EFI exhaust and Crane 262 ( I believe ) cam. So the MPG's did seem to be up a bit and now they're down. So the other issue that I'm having is it has a brand new radiator , water pump and thermostat in it yet it still seems to be running too high of a temp. So someone told me to re adjust the timing as that could be causing the overheating issue. Anyone know if that's possible or not ? I haven't had a chance to re look at the carb or anything yet to work on fixing it yet but just wanted to check around and see what might be the problem for both the temp and the low MPG's. I think that I'm going to adjust and re jet the carb and not sure yet about the overheating. I'd like a bigger radiator in it but the new one in it is the same size as the original one was. Any help ?

 

When is it over heating? Idle and slow speed or while at highway speeds?

Stock temp gauge or after market? Could be a gauge or sending unit giving false reading.

Was it running hot before you changed all of those components? Faulty thermostat? You can take it out and drop in a cup of boiling water and see if it opens.

Take care,

 

It overheats most all of the time, running 190-200. Low speeds once it warms up, and at speed or at idle. Once it warms up all the way to 190-200 it doesn't come back down at all. It is a aftermarket gauge as I installed the Dakota Digital Dash and it came with electric sending units. I guess it could be faulty. It had stock dash/gauges before the rebuild and upgrades and didn't run hot then. With the rebuild and upgrades I replaced: carb, intake, cam, exhaust, water pump, alternator, starter, radiator, and master cylinder, shocks, tires, exhaust system, seat and new window seals. The new radiator is stock so I'm wondering if I need to get something bigger. It has a very small shroud and I did replace the stock fan with a flex fan. Any ideas on that ? Any chance the carb adjustment or being out of adjustment and the timing could have anything to do with it ? Or should I check the thermostat and replace the sending unit first you think ?

 

Well crap,....

What temp thermostat are you running? Stock is around 192*..... so if you are indicating 190-200 then this may be normal and you don't really have an over temp problem.

I myself am not a fan of flex fans as they age they flex at to low an rpm causing problems.

As for Carb adjustments.... just make sure that the choke opens all the way when warm.

As for Timing,... I have seen where timing can cause Temp issues.... just verify that you have ~10* at Idle with the Vac advance line removed and plugged.

After re-reading your last post,... considering that the temp is about the same either at slow speed (idle) or high speed,.... 190-200.... I don't know if you even have a problem.

When you shut it down and pop the hood,... do you hear and faint boiling sounds?

As a last resort you can always buy a cheap IR Temp gun and shoot the radiator and compare the reading you get with the reading on yer Temp gauge.

Let us know what yo find,

 

Thanks Lee, I'll check it out. I haven't ran it in a few days but I'll be using it this weekend so I'll check it out then and see. I don't think that I remember hearing any boiling sounds but I'll check, and I'll check the timing. I'm sure that the choke is open it's just that I think it's running too rich and lower MPG than I should be getting or than what I was getting before. Probably a different issue all together. Thanks for your help and I'll check it out this weekend and let you know. Thanks again.

 

Is the fan facing the right way? If it's for a reverse-rotation water pump, it won't work right on a standard-rotation.
Retarded timing can heat them up, as can a lean mixture.

Does it smell hot?

If you still have the parts, I'd pop the stock temp gauge sender back on there and connect the stock gauge's wire, and see what that indicates.

What temperature is your thermostat rated at?

 

Try a cooler 180 temp thermostat, the cam oversized can cause this, I change mine depending on the season and it helps, or at least it did on my 302

 

You have a lot of good advice. Just "follow up" and let us know what you find.

Retarded ignition timing can contribute to overheating.

My opinion is, if you live in a place in the world where it gets "hot", you can't have too big of a radiator.

190-200F is "normal" if you have a high temperature thermostat. Thermostats are available down to 160F, generally.

On rebuilt engines, especially over-bores, things can be set a bit too "tight" resulting in higher operating temperatures.

It's always good to verify a temperature gauge.

Flex fans may have some problems, but they usually move as much air as a fixed factory fan or sad working clutch fan, at least when they're new.

Don't assume that something is "good" just because it's new. Try to verify component performance.

 

Engine is bored 20 over, just now has 6000 miles on the fresh new rebuild. The flex fan is facing the correct way but I have wondered about changing it to a solid type fan just in case it doesn't pull enough air through it. I would say the carb adjustment right now is running too rich, not too lean and I'll check the timing but haven't got to that yet. I am pretty positive that I put a 180 thermostat in it, but have wondered and been thinking about going down to a 160 just to see or replace the 180 just in case it's bad. But have wondered about a bigger radiator also just to give it a bit of extra. I'll know more tonight or tomorrow and report back and thanks for all the help and input guys. Work in progress.......

 

ok so it's time for an update here. I drove the truck this weekend and it still seemed to run 190-200 on the highway, maybe closer to 190 when at slower speeds. I was on my way home when it started to rain and turned on the wipers along with the heater/defroster and instantly the temp dropped to just barely above 180. down from close to 200. any other tips or ideas ? I'm going to check on the thermostat and maybe replace that and the fan as soon as I have time to get around to it. Just wondering what else I should check on it, when I have time probably next weekend. Thanks guys.

 

When you turn on the heater it puts a "slug" of cool water into the system and gives the hot water another place to go (the heater core). Hence, the temperature drop. Checking the thermostat is a good idea. You may want to invest a few dollars in a new 160 model.

 

190°-200° is a normal operating temp. A 180° stat starts to open at 192° it is not open at 180°
And yes timing will affect engine temperature, if it is not advanced enough the engine will run hot.
Since the engine is still new it will run a bit warm until things are loosened up and broken in just due to increased friction on the cylinder walls.

Ideally you want as hot a thermostat as your motor/cooling system can stand, As engine temp drops cylinder wear increases and combustion efficiency drops. 160° is way to cold for street driven vehicles as cylinder wear is greatly increased a those lower temps.. Additionally Flex fans are great for around town not so much on the hyway as they can slow the flow of air through the radiator. This is why they fell out of favour for clutch fans in the early 80's with the increased engine operating temps.

You may also be running a bit lean on the carb , check your plugs and if they are showing signs of high combustion temps adjust the fuel air mix.

There is a reason you are running a bit warmer than you should be with a 180° stat, just changing to a lower temp stat does not solve the underlying issue and just masks it. If it is a lean condition or timing issue and you do not address it the eventual outcome will be burnt exhaust valves.
If the engine was not hot tanked but just run through the Baco there could be garbage coming out of the block restricting the rad so just cause the rad is new does not mean it is not restricted. I will not use ANY engine re-builder that does not hot tank engine castings prior to rebuild.

 

I will call and ask if the engine block was hot tanked or not when it was rebuilt. I will hopefully have some time this weekend to get to it and check the timing etc and maybe check the thermostat and see about getting a new one and a new fan, maybe flush the cooling system and have to see about the carb adjustment too. Now I at least have some more info on what all I should be checking for when I get around to it. Thanks guys.