"New truck" Overheat.. Ideas?

[G. Mann]

Ok.. got a "new" truck. 1987 F-250 XLT HD 4x4 SRW. 6.9 engine, T19 4 speed trans [not sure which transfer case it has yet]. It has the extended cab, long bed.

It has an 8 ft cab over camper. [no overhang out the back, only bed length. Cab over part fits the extended cab.

Just rebuilt the front end, brakes, etc etc.. all the items the previous owners neglected. Went up the mountains for a test drive [about 300 miles, all uphill]. On the first long pull, heated up to point of blowing fluid out the overflow fill tank and making steam.

Cooled it down. Added water, drove on. As the drive continued, the temp would go to to high.. then it would quickly cool down... then overheat again.. then quickly cool down..

Question: Is this a classic case of the wrong thermostat? Did Autozone do one again?

Radiator looks clean, cooling fluid looks not contaminated, and when it finally starts to cool, it works like an IDI radiator should.

Comments and helpful hints welcome please. Before I start throwing $$$$$ at it till it's fixed.

 

[gatorman21218]

Yes the wisdom here says the only t-stat that fits is from Ford or Navistar.

Try a OEM part and then go from there.

 

[Iowa 73]

Check the fan clutch. How old is the water pump: grab the fan and try to move it up and down to check the condition of the water pump bearing.
Also, the Motorcraft thermostat is the only one recommended for these engines.

 

[riotwarrior]

Autozone thermostat is NOT worth using...get a real motorcraft or IHI stat in there ASAP and try again!

Also did you hear the fan kicking in? If it wasn't kicking in that could play havock too.

How are the core tubes in rad? clear of full of gunk?

There are many questions to go through before suggesting much.

Al

 

[G. Mann]

Thanks, good idea. Just checked the fan clutch and water pump bearing play. Pump bearings seem OK. Fan clutch is doing what it should. So it's looking more and more like the wrong thermostat issue.

Just ran a piece of .040 stainless safety wire [turned the end back on it's self so it was rounded into a tight loop, no pokey end to hurt the radiator] down the core slots that I could reach from the radiator cap hole.. it all came back clean and no obstructions felt. [measured the wire probe against the upper and lower radiator tank distance. Based on that, I'm taking a bet the radiator is clear.

 

[hesutton]

You gotta give the entire cooling system a good look.

The water pump leaking or have a trail of brown crap ozzing from the bearings weep hole on the bottom?

T-stat as stated above should be only from Ford or IH.

Hoses....... leaks, balloning? Any chance the lower hose doesn't have a spring in it and it's collapsing restricting flow?

How bout the radiator? Is there a bunch of scale and precipitate on the tubes? The chances that the previous owner or owners always and only used distilled water for the coolant in slim. That stuff can really hurt the efficency of the radiator. When it's heavy on the rad, it's hard to get it out and a replacement is the best option.

The fan clutch should lock up when the engine gets hot. If not, if can let it get too hot.

The coolant mixed correctly? How old is it?


Does that 6.9 have the original headgaskets? If so, and I hate to say it, a leaking headgasket could be the problem. It can run fine with "normal" driving, but will get hot and spew coolant with loaded/working hard. I had that happen to mine.

Do you have a proper coolant temp gauge? Don't trust the factory gauge.


Heath

 

[PackRat239]

In this case, the fan doesn't come into play, as it does nothing to cool the rad when the truck is at speed. Is the cooling system FULL? if it has an air bubble or is otherwise low, it will do exactly what you describe.

 

[icanfixall]

May have to check the thremostat. The factory stats open at 192 degree and are fully open at 212 degrees. If your going to pull it just make sure you have the factory stat and gasket on hand. Its a bigger job that on a gas chevy small block. I'm guessing you don't have a gauge telling you what the temp was. The dash gauge is not very reliable so please install a real gauge. Who knows what the letter l means or the letter n means for temps. If you choose to change the coolant use only steam distilled water. It wont conduct electricity nor will it loose minerals in the radiater. The bottom hose needs a spring. Some bottom hoses come without a spring because they are supposed to not need one... Sorry but I just gotta fly the flag on that one. Keep us posted on what you do to fix it.

 

[Hydro-idi]

I would definitely check the thermostat and replace with a motorcraft one and nothing else. If that doesn't fix the engine temp fluctuation and overheating, I am leaning towards your engine experiencing a head gasket failure. When head gaskets let go, it is common to see coolant temp fluctuation like you are experiencing.....along with many other bad things lol.

 

[G. Mann]

Thanks to everyone who replied so far.

Good points on checking the old thermostat even though I'm going to replace it. I have a laser digital thermometer so easy to do with a pan of water and a gas stove.. Just monitor the temp and watch the movement. I'll do that and report back. Will be couple days before I can get to it.. that ugly 4 letter word "work" gets in the way..

Help me on the possible head gasket issue. Those who have had a head gasket fail, did you see a rise in radiator pressure along with the rise in temp? Also, with the engine running and still cold, did you see bubbles coming out of the radiator cap hole with the cap off? I'm not seeing these but maybe the gasket leak is still small ??
Goes without saying.. I don't want to pull heads if I don't have to. Engine on the truck is "supposed to be fresh rebuild with about 40,000 miles on it. [and sellers never lie.. right?}

 

[icanfixall]

A seller never lies.. Mon o man is that right up off the stable floor. With 40,000 on the fresh rebuild one has to ask did the builder really take the time and knew to bottom tap all the head bolt hole threads.. Or just a wash and install with some oil job. What you do not want to do is run or long periods with a bad head gasket. The hot compression can cut the block. Then you have a mess to make a clean cut on the block..

 

[Wicked97]

In this case, the fan doesn't come into play, as it does nothing to cool the rad when the truck is at speed. Is the cooling system FULL? if it has an air bubble or is otherwise low, it will do exactly what you describe.

I'm sorry but that is dead wrong. If your pulling hills or even in wind with a good load they will get hot with a bad fan clutch. The fan does far more than you think on the highway when your actually working it.

 

[icanfixall]

I was waiting for someone to post the above about the usefulness of the fan.. When I have pulled long grades heavy I watch the temps go up. Then hear the fan lock up and sound like a B24 engine sucking in the air. then it quites down as the temp drops but I'm stil l climbing the grade.. Kinda wierd but it works just fine..

 

[058hammer]

Has the fuel been turned up?

 

[dmaxjoe]

Has the fuel been turned up?

Get a Pyrometer and watch egts. Just to be safe. But I think you have classic symptoms of bad fan clutch. You most definately want a Motorcraft thermostat. Pricey but worth it.