Hi guys,

New to the forum here, but check it out regularly when I run into a problem. I've got one that's got me stumped. It all started when I changed out the fuel pump. Thought I had everything good to go, but the old truck started running hot. It's a 79 300 straight 6 engine. I have replaced water pump, thermostat, water neck (because I broke the original one), radiator cap, temp sensor. I did a coolant system flush. Cut out the muffler to see if it was stopped up and causing overheating. No water in the floorboard to indicate a bad heater core. Here's the weird thing, when I adjust the timing (by turning the distributor) and adjust it down, the temp goes down. When I rev the engine up, temp goes up. If I bump the timing down to where she's just barely running, the temp gauge gets within operating range, but when I rev the engine it goes back to overheating. I was able to get it to stay in operating range yesterday by removing the thermostat when I was doing the coolant system flush. But, put the tstat back in this morning and she's still overheating. I am completely lost. Anybody got any ideas as to what else I can do? Thanks in advance for any help or insight.

 

Maybe the head gasket started leaking.

By retarding the timing you reduced the cylinder pressure enough to keep the gasket from leaking. By increasing the timing back to spec you raised the cylinder pressure enough to start leakage past the gasket. Have you lost any coolant from the recovery bottle?

 

Is it actually getting hot enough to spit water or is it just the gauge showing the engine is hot? Any verification with a temp gun or manual gauge?

 

I hope that's not it. There is no recovery bottle, if I'm understanding you correctly. Just an overflow hose running from the radiator cap neck down the side of the radiator.

 

Yes, it is getting hot enough to spit some water, but I haven't let it run very long after it starts showing hot. No verification with a temp gun or manual gauge, don't have either of those. What I did do, it loosen the lower radiator hose (while it was running at normal temp yesterday without the tstat in), and let it spray some water out, when it got low, it started showing hot, when I added water it started running cooler. If you are thinking that the gauge may be bad, my fuel gauge pegs out when the tank is full, that's new too.

 

Retarded (late) ignition timing will cause high temperatures, especially exhaust manifolds. Make sure the ignition timing, the internal distributor advance, is advancing correctly throughout the RPM range. It sort of sounds like it might be stuck? It would probably run very poor out on the road though.

 

You need a coolant recovery bottle.

Every vehicle needs a coolant recovery bottle.

I'm not saying it will cure your problem. I think it's beyond that. I think your head gasket is toast. Don't fret - that is a relatively cheap fix.
IFF - you don't let it go so long you warp / crack the cylinder head!

 

The only trucks that came standard equipment with a coolant recovery reservoir were 1971/74 F100 2WD 240 I-6 with a M/T (D1TZ-8A080-A).

If people wanted a reservoir, Ford offered a "universal fitz-all" at the parts counter (D0AZ-8522-A), auto parts stores also sold them.

 

I know. My '85 Club Wagon did not come with one. Interestingly, it would lose coolant over time. Maybe a quart or two over the summertime. When I realized something was up the level in the radiator was about eight inches low. I never figured out where all the coolant went. It did not show any signs of leakage out any of the many coolant connections (had two heaters front and rear).
It did not show leakage around the water pump.
It did not show any signs of head gasket leakage (no coolant blasted spark plugs) or external traces of coolant leaks of any sort.
A complete mystery to me, but every year was the same thing - large loss of coolant. But no effect on engine performance.

I added a coolant recovery bottle. After that the level would stay full in the radiator. Of course the level in the coolant recovery bottle would deplete and I would periodically replenish it. It was cheaper, less risky, and easier than tearing down the engine and looking for - what??? - cracks?, head gasket?

IN GENERAL, A COOLANT RECOVERY BOTTLE WILL IMPROVE THE EFFICIENCY OF A COOLING SYSTEM BY 10%. THIS IS BECAUSE EVENTUALLY ALL AIR WILL BE BLED FROM THE COOLANT SYSTEM. WITHOUT A COOLANT RECOVERY BOTTLE THERE WILL ALWAYS BE SOME AIR IN THE SYSTEM FROM THE THERMAL EXPANSION OF THE COOLANT. THIS AIR DOES NOT JUST SIT THERE IN THE TOP OF THE RADIATOR. IT MIXES WITH THE COOLANT CREATING A FOAMY FROTH THAT IS NOT AS EFFICIENT AS SOLID LIQUID AT REMOVING ENGINE HEAT.