Very strange temperature issue. Tried searching and couldn't find anyone ever having a similar problem.

[Darksoldier]

I have a 96 XLT with the 4.0 OHV. I recently replaced the heater control valve as it was leaking. Bled it several times with one of those spill free funnels as I usually do on every vehicle. When I start it cold it heats up to around 220 and occasionally 230 before the thermostat opens. Then it drops all the way down to 170 the first time. As the radiator gets warmer the thermostat will open at like 215 and drop down to like 180. Then 210 and 185. And eventually it stabalizes to around a normal 194-203 degrees with very little fluctuation. The thermostat used to ALWAYS open a little over 200 degrees. These are the temps from an OBD scanner and I verified them with a temperature gun at the thermostat housing. I was thinking it could be the thermostat but I feel if it was bad and simply opening late it would heat up to 220 or more every time. Any ideas what could be causing this?

 

[donalds]

I'd buy a new thermostat and be done with it!!

 

[Darksoldier]

I'd buy a new thermostat and be done with it!!

But how could a bad thermostat consistently stabilize to perfect temps after several heat cycles? Anything else that could cause this?

 

[donalds]

What kind of t-stat did you use ?

Also a bad fan clutch would do this also

Your temp are way to high

 

[Pete Deering]

What kind of t-stat did you use ?

Also a bad fan clutch would do this also

Your temp are way to high

I had the same problem. The cause is air trap in the upper manifold. I also uses the spill free funnels. You also need a vacuum bleeder, that get all the air out. One thing you can do, is park your vehicle on a hill ( incline) so your funnel is at the highest point. Or lift the front end up in the air, so the funnel is at the highest point. There is a technical service bulletin about this issue. Ford has a bypass hose and fitting. The dealer installed it on my car under warranty. I remove It some years later, because I could not maintain it. I used the vacuum bleeder and spill free funnels. That system solve the issue.

 

[Darksoldier]

What kind of t-stat did you use ?

Also a bad fan clutch would do this also

Your temp are way to high

The t-stat is what ever was put in it when the engine was changed with a jasper engine by the previous owner. Not sure if it would be listed in the paperwork I have. It is either a 195 or 197 degree but not sure if it is OEM. Radiator is still at like 140 degrees or less when it does this and it goes away after running longer so don't think the fan has anything to do with it. How high exactly should a normal temp on these be? I have had it a couple years now and I'm pretty sure it never went above 205 before but 220 seems to be the center of the gauge which is strange.

 

[Darksoldier]

I had the same problem. The cause is air trap in the upper manifold. I also uses the spill free funnels. You also need a vacuum bleeder, that get all the air out. One thing you can do, is park your vehicle on a hill ( incline) so your funnel is at the highest point. Or lift the front end up in the air, so the funnel is at the highest point. There is a technical service bulletin about this issue. Ford has a bypass hose and fitting. The dealer installed it on my car under warranty. I remove It some years later, because I could not maintain it. I used the vacuum bleeder and spill free funnels. That system solve the issue.

That's what I initially was thinking but I bled it so much on that funnel I didn't see how air could still be trapped. Good to know it still could be. I didn't jack up the truck figuring the funnel would automatically be the highest point but maybe not. I can try that. I haven't used a vacuum bleeder for a coolant system before. Is one expensive? Can I just hook a mityvac up to it with an adapter? Also, I did see that TSB but it seemed to be about much wilder temperature swings and water hammering noises which I don't have.

 

[donalds]

Why risk this engine over a unknown t-stat
Buy a new good one
Actually take a look at the fan clutch operation test it
Guessing won't work just saying

 

[Darksoldier]

Why risk this engine over a unknown t-stat
Buy a new good one
Actually take a look at the fan clutch operation test it
Guessing won't work just saying

This truck is real rusty. It doesn't help that I got it stuck once in water that came almost up to the top of the center console either. Kinda afraid one of the bolts will snap off on the thermostat. Lol. I will change it if bleeding it more still doesn't work. As far as the fan it was working fine when I changed the cracked blades not too long ago and it will still do this even at highway speeds plus it is pretty cold outside.

 

[donalds]

So the truck was under water
The engine running fan can't turn so
The fan clutch is where I'd look first
not saying that's your problem
The temps level out because your moving down the road
and don't need a fan at that point

TEST IT !

 

[Darksoldier]

So the truck was under water
The engine running fan can't turn so
The fan clutch is where I'd look first
not saying that's your problem
The temps level out because your moving down the road
and don't need a fan at that point

TEST IT !

It was quite awhile back now but I see how that could have messed up the fan. What is the proper way to test the clutch? Sending it around the 8 track and getting it airbourne with what I later found out was a messed up cv axle wouldn't effect the fan would it? It does still spike like that then level out just idling in my driveway though.

 

[Darksoldier]

So the truck was under water
The engine running fan can't turn so
The fan clutch is where I'd look first
not saying that's your problem
The temps level out because your moving down the road
and don't need a fan at that point

TEST IT !

I just ran it now for a bit. I can hear the fan speed increase at about 210 degrees. Maybe it is supossed to be earlier than that?

Edit. Nevermind that is the rpm increasing. If I put my hand behind the fan it seems to be moving a ton of air regardless.

 

[donalds]

I just ran it now for a bit. I can hear the fan speed increase at about 210 degrees. Maybe it is supossed to be earlier than that?

Edit. Nevermind that is the rpm increasing. If I put my hand behind the fan it seems to be moving a ton of air regardless.

Next step new t-stat and a flush IMO

 

[Darksoldier]

Next step new t-stat and a flush IMO

I'm going to try and bleed it again tomorrow with it jacked up. If that doesn't work I'll try the thermostat.

 

[Mbrooks420]

Agreed. Thermostat to start, after you’re positive there’s no air bubble.

 

[Darksoldier]

-

 

[Darksoldier]

Next step new t-stat and a flush IMO

I know I said I was going to try bleeding it again today but I forgot to steal the funnel from work when I got out.

 

[fast_dave]

@Darksoldier

Change to a new, STANT Brand thermostat and then test the fan clutch, or vice versa

The 4 Liter Engine cooling systems are VERY fan clutch dependent.

Old School Fan Clutch Performance Test
Bring truck up to operating temperature.
Fold over an old section of 5/8" heater hose so it's about a foot long when doubled over.
With engine idling, and being aware of engine compartment surroundings, carefully insert the folded over hose in the path of the fan blades.
If the clutch is good, it will easily overcome the resistance of the heater hose, and act like it's a playing card on bicycle wheel spokes.
If the clutch is bad, the fan will stop spinning as the engine continues to idle.

If you need a new fan clutch, HAYDEN Brand Model #2794 is the OEM Ford Manufacturer Clutch (without the FORD ink marking/stamp).

$42 @ Rock Auto and then utilize a 5% Discount Code.

Same fan clutch will be $80 in the Auto Parts Store.

Hope that helps -

PS - LOVE the pics - absolutely epic - the only thing missing are Police & Fire!!!

 

[Darksoldier]

Change to a new, STANT Brand thermostat and then test the fan clutch, or vice versa

The 4 Liter Engine cooling systems are VERY fan clutch dependent.

Old School Fan Clutch Performance Test
Bring truck up to operating temperature.
Fold over an old section of 5/8" heater hose so it's about a foot long when doubled over.
With engine idling, and being aware of engine compartment surroundings, carefully insert the folded over hose in the path of the fan blades.
If the clutch is good, it will easily overcome the resistance of the heater hose, and act like it's a playing card on bicycle wheel spokes.
If the clutch is bad, the fan will stop spinning as the engine continues to idle.

If you need a new fan clutch, HAYDEN Brand Model #2794 is the OEM Ford Manufacturer Clutch (without the FORD ink marking/stamp).

$42 @ Rock Auto and then utilize a 5% Discount Code.

Same fan clutch will be $80 in the Auto Parts Store.

Hope that helps -

PS - LOVE the pics - absolutely epic - the only thing missing are Police & Fire!!!

I thought the STANT one didn't have the little air bleed valve. I was going to try and find an OEM one. Are you sure that fan clutch test won't hurt the plastic fan blades? Awesome tip on the Hayden clutch being OEM by the way. I may just order one anyway. Didn't realize a quality one could be had so cheap. The fan does seem to be moving a lot of air though.

 

[Darksoldier]

Change to a new, STANT Brand thermostat and then test the fan clutch, or vice versa

The 4 Liter Engine cooling systems are VERY fan clutch dependent.

Old School Fan Clutch Performance Test
Bring truck up to operating temperature.
Fold over an old section of 5/8" heater hose so it's about a foot long when doubled over.
With engine idling, and being aware of engine compartment surroundings, carefully insert the folded over hose in the path of the fan blades.
If the clutch is good, it will easily overcome the resistance of the heater hose, and act like it's a playing card on bicycle wheel spokes.
If the clutch is bad, the fan will stop spinning as the engine continues to idle.

If you need a new fan clutch, HAYDEN Brand Model #2794 is the OEM Ford Manufacturer Clutch (without the FORD ink marking/stamp).

$42 @ Rock Auto and then utilize a 5% Discount Code.

Same fan clutch will be $80 in the Auto Parts Store.

Hope that helps -

PS - LOVE the pics - absolutely epic - the only thing missing are Police & Fire!!!

As far as the pics there were no police or fire involved lol. I was about 6 miles deep into the forest and I didn't think the water was that deep till I got stuck in it. Believe it or not I winched that out of that water by hand with a come along only to find out the battery was then dead and I didn't have my jump box. Me and my passengers then hiked all the way out of there to a gas station on the main road to try and get help. No one dared to drive back there. I finally got a friend to come up with his F150 the next afternoon and we drove back to the truck expecting to be faced with the difficult task of towing it out of there. Against my better judgment and on no sleep we checked the fluids, dumped some water out of the airbox, then gave it a jump and I couldn't believe it when it fired right up, sputtered only a little, then smoothed right out before I drove it out of there. I always used to be a GM guy but I guess they weren't lying when they said built Ford tough. Of course I had to go through the truck after. The entire interior had to be shampooed and dried as much as possible and it took almost a week for it to dry out completly. I had problems with the windows and sunroof not working and the 4wd light flashing when I tried to turn it on and the fuse under the hood for them would blow immediately. I ended up unplugging the power seats replaced the fuse and everything else worked again. Oh and I had one o2 sensor go bad a week later. I never did try plugging the seats back in again.