1998 2.5L, swapped thermostat(old one literally was cracked in two by the tan that holds it into the plastic housing). Put a stant one in from local auto parts store..what a joke. took that back out and installed a new oem ford one(fit's great, has nice snug fit in the press area of plastic housing and sits in there perfect). well it's been over a week now, i have heat no complaints there, but if it sits for a while, say a stop light or such, and then you go shift through the gears and accelerate, it drops temp on the gauge. not all the way down to COLD, but it drops a big amount, normal driving it sits just a shade under the middle. This doesn't seem to be affecting anything, but just bugs the **** outa me! Coolant has no air in system as it isn't taking any extra from the resovior and the radiator isn't dropping.

What's going on here or what did i miss when i did the thermostat? I can't think what could be causing this..

 

What temp thermostat did you put in? Lower temp thermostat will open earlier and upon WOT it will drop siginificantly.

In my car, I went from an OEm 180 degree to Gates 160 and at WOT on a 30 degree day.....my engine temps went from 190 down to 140!.....NOT good to drop that much that fast....metal tends to crack. Also, quick drops will change pressures in the cylinder head slightly, which could cause what happened to my car (although it was aluminum head and block).....both separated due to constant temperature fluctuation and eventually stripped the headbolts.

 

I put in the oem ford one, 192 it said. Old one was the same...

 

Hmmm.....and you burped the system enough to ensure there's no air? Usually, if the temp of thermostat is not the culprit, trapped air pockets are.

Make sure the nose is higher than the rear and open the rad cap when cold. Start the truck and let it just idle for about 15-20 minutes to fully ensure all air is burped out.

 

I "thought" all air was out, been driving for over a week and it quit taking water from the reservoir on wheel well. So I just assumed no more air?! I'm bout ready to pull it apart again, this is ridiculous. I don't wanna wreck something. Scanner showed it dropping to about 179 while sitting still, then all the way up to 201 during driving or acceleration...

 

I flushed my car out and didn't find the air leak until about 3 weeks later, when temps ranged from 171-190 driving and 240 at idle.

I haven't cracked mine open yet, but do the OEM thermostats have "jiggle" valves? Those help the system bleed air bubbles out, but they need to be in the correct position to work.

 

Mybe your fan clutch is bad and fan is running all the time.

 

I had a bad fan clutch on a different ranger, got real tight and stumbled to turn. The fan clutch on this ranger is still nice and smooth, spins just how it's suppose to; so i'd call that good i guess.

 

After taking thermostat out again, putting in water and visually watching it open at about 190, and close again, VERY slowly, took it and out it back in. Problem still there. Could it be defective, should I order another from ford? I know I only saw 20 degrees fluctuation according to scanner, and I don't think that's enough to crack metal, but this is driving me crazy!! This is stuff I'd expect in zero or below weather, not 20-30 degree temps

 

May be wrong forum to post this, but does these 2.5 engines have coolant passing through I take manifold? Just thinkin if coolant could be leaking somewhere and I know ppl have talked about intake manifolds leaking coolant, on v engines(v6, v8). Do our inline 4 cylinders have coolant passing through? I don't think this is an issue as I'm not using coolant, and if I am, it's not noticeable. Just felt better seeing what you guys thought

 

Sounds the impellers are corroded away in the water pump.

 

Is that possible? Wouldn't that slow or stop flow through the system?

 

Anybody else know how or if a bad water pump could cause this?