Fellers I haven't been around inn'a while but hadda stop back to pick your collective brains. 1986 F-150 302/AOD/EFI/Lariot. A while back the temp. was gitting high enough it was making me nervous. Not exactlly pinning the needle but on the right side of the NORMAL lettering and approaching the hot zone. I only drive 7 miles to work...but I could cook a whole chicken just by setting it on the dash with the defroster on and the switch on high. So I took it to my mechanic and he changed out the thermostat...said he put in a lower temp one. Since then the temp. gauge barely moves. I mean it's laying all the way to the left...on cold...24/7. Been this way now for...ohhhh...500 miles. Now the trouble starts. Trucks won't idle/ REEKS of unburnt fuel/ croaks/stutters/gas milage sucks. Back to the garage. $600 later...lots of new sensors, adjustments, cleaners, fuel filters, sparkplugs, (fuel-fowled) and sundry other things. It's running better..but still balky. Drove it home today (7 miles) removed the radiator cap and stuck my finger in the lukewarm anti-freeze. I see a problem here. My guess is the thermostat is stuck open, engine never gets to operating temp and computor has it running rich/enriched...what we used to call choked on a carbed engine. Am I reading this right? Thanks in advance. Audie...the Oldfart..

 

Either its stuck or its to low of a thermostat and is opening to early.

 

I would have to agree with that.

 

The fact that the engine was running overly hot until the thermostat was changed, indicates that it was faulty; but almost the worst thing for an engine, is to be running cold.
Apart from poor mileage & driveability, bore wear is a lot more rapid when the engine is below proper operating temperature (195deg in these motors).

A properly operating thermostat prevents the engine from running too cold - but the fan, radiator & water pump provide the cooling.

 

If you are relying on the factory gauge to tell you the engine temperature, you may be wasting your time with thermostats.

I would want to verify anything a factory gauge tells me, especially if they all seem to be reading high or low at the same time (in which case the ICVR is likely at fault).

 

I will only use genuine Ford thermostats for now on. Long story short, three diff. thermostats, no heat. Put in a Ford one, great heat. IMO, the aftermarket ones are junk. My cooling system and heater core was spotless.

 

As with other things, sometimes the aftermarket ones are just as good or better than, and sometimes you just gotta go with the original equipment ones.

 

Folks thanks for the quick replies. As I surmised this needs to be corrected before I drive or the same results will happen again. I'll pick up a new thermostat/gasket and manual guage hopefully this weekend. I don't need the truck as it's mostly used only in hunting season an hauling material for home repairs. (1400 miles driven last year...) I will agree that it does not bode well to trust the factory guages but when one can drive 7 miles and the temp of the anti-freeze is 85/90 degrees...eh? I looked at the area needing attention and presume the easiest way to r/r the thermostat would be to remove the entire engine....thanks again Ford Motor Company!! Anyone know of a good tutorial/video concerning such an undertaking? Checked youtube and not much help there. The last time it cost me $75...but might be safer tojust pay the mechanic...again. Thanks to all. Audie..the Oldfart

 

you said 302 right? Replacing the thermostat should be pretty straight forward. Thermostat housing is on the front of the intake manifold. 2 bolts and it should come right off.

Is there something about the 86' 302 that is different than all the others?

 

If you get a genuine t/stat (or genuine style) it will twist-lock into the housing, making installation easy.
Otherwise it's difficult to get everything in place without having the gasket shift & then leak.

 

Was reading on this issue and it stated that some thermostats have a "Lock Open" or "fail open" state where under certain circumstanses it will lock open. In this article they were stating how a lot of aftermarket thermostats where doing this very early for no apparent reason. They showed pictures where a thermostat was wide open after one heat cycle. You could clearly see it was stuck open.
apparently this is a feature that if the spring is weakening, it goes to this state rather then staying shut. Sounds like a good feature...as long as it's doing it when its supposed to rathern then after one use.

 

1992 Ford F-150 Pickup Thermostat Replacement (part 2) - YouTube

 

Ken this is exactlly what I wanted to know!! Everything I've read so far about broken t'stat housings, leaks etc. etc. stems from the new thermostat shifting upon installation. Handy piece of info there...many thanks! Audie...the Oldfart..

 

82f there's probably not a whole lot of difference in the V-8's . The area is impossibly cramped and the waterpump housing is in the way of the lower bolt on the t'stat housing. I've done a number of them on inline 6's and yeah...that's easy. Even getting in to clean up the area where it mounts on the block looks like a p.i.t.a. on this engine. I'll see what I can take off without horribly gammahoochin' this up to make it easier. My first worry is snapping off a bolt/stud where I can't get to it. I'll soak everything below the windshield in penetrating oil before I start. My last little attempt was replacing a bad 4-way flasher relay....ohh yeah....that went well. Upside down (I have vertigo) crammed under the dash....back spasm hit and left me laying in the driveway for 30 minutes. It was 18 degrees that day. Audie...the Oldfart....

 

I gotcha....I guess I read your comment about removing the entire engine too literally.