Temperature fluctuation, thumping / thugging noise engine off

[WMX267]

Hello there!

I'll go straight.

Replaced the water pump because of a worn out shaft. After installation, I noticed that the temp would drop a little and then go back to normal. Ignored it for a while and then heard the thumping noise. At one point, the upper hose was pumping (as in collapsing and expanding) even after switching the engine off. I decided to change the thermostat after that as I thought the vacuum was trying to such h20, but the old tstat wasn't opening.

Installed it and still the same noise and dropping of temperature, but now, it would seem like it would want to overheat, and then the tstat would open (theoretically), so it would go all the way down, and slowly come back to normal.

Tried bleeding/burping the system already (I hope I did it right), but haven't gotten better results. Do I just let the engine idle when burping or is it fine to have it @ 2000rpm?

I got squirted with coolant when it shot out. This is the tstat opening right?

I understand a worse case scenario would be gaskets. Just on the heads? or would intake / exhaust gaskets also cause this?

I can't exactly say that it's related to the airconditioning. Could it? How? But somehow I think it's aggravated when the compressor is on load. Otherwise, would there still be a connection? I refilled my A/C refrigerant prior to this, if that matters.

I'll try completely flushing the system when it gets warmer (Calgary), but other than this, what could be causing it?

Could be the coolant sending unit. Testing is decrease in ohms with rise in temp right? Now it that the one that goes to the dash? And there's another one going to the OBD right? Or could there be just one?

I know those are a lot of questions. On top of fixing it, I want to know how the system works or what's causing it not to work and how. Thanks in advance.

I would want to still have it when I say, "Oh that's the problem!"

1997 Ford Explorer 4.0 V6 OHV

[WMX267]

I noticed that it still happens even with the blower / heater off, but it's not really that noticeable - I'm figuring it might be from the temperature outside lowering the coolant too much before it enters the engine again, plus, it's not accompanied by the thumping sound. BTW, the collapsing of the upper radiator hose has stopped, but there's still the thumping - sounds like it's coming from below the engine compartment. Basically, with the heater off, it doesn't go all the way down.

I checked the fan clutch and it seemed okay to me. Vehicle off and cold, it doesn't rotate freely, but it is movable by hand with the limited amount of space. It would barely make it 1 1/2 a turn though. Should it be more free? I could have overtightened the big bolt to the h20 pump when I replaced the h20 pump. Could this be the problem or matter?

Anyway, after starting the engine, it (the fan) starts to engage immediately and after shutting the engine off, it would rotate a good 1-2 seconds before stopping. Does this look fine?

I haven't checked the sending unit thinking that it doesn't explain the thumping noise. A faulty thermostat could not be it as well since it's new, it opens and closes and coolant circulates.

I'm lost here. I hope somebody can bring up more ideas, or a more systematic approach to diagnosing. Thank you very much.

[WMX267]

OK. So I"ve drained the coolant and flushed it. It's now filled. One thing I noticed before I drained the old coolant is that when I have the problem, and I rev the engine, the lower and upper radiator hoses collapse as if it's being squeezed inward by the suction of the water pump. This doesn't happen when the engine is in it's normal state.

The temperature dropped one more time while I was burping the system. The temperature dropped, revving caused the hoses to collapse, later, thumping, and then went back to normal. It didn't do it again until I was satisfied that the system had no air.

I'll see tomorrow if it will do it again.

What could go wrong or what do I check on the radiator which could possibly cause the symptoms? I don't think it's clogged as it drained pretty well and I know the coolant is able to circulate.

I'll try to see if I have time tomorrow to do some more... I don't know. Thinking. Checking.

[WMX267]

I wonder if a worn out hose could be a factor here? It shouldn't be collapsing like I described should it? If the hose has been worn out through time and is too soft, could this be causing the problem? Just thinking.

Somebody help me please. lol.

[inafogg]

when did this problem begin??was it ok before w/p replacement??it does sound like air
is traped in system.it could be a clogged radiator.with the engine @ operating temp
feel top & bottom of radiator they should be the same temp.if its ok try running with rad cap off to make sure air is out.if it starts over flowing gushing out radiator more than normal suspect a restricted/clogg in rad.whats the mileage

[scoobytuff]

I'll have to look it up again, but there was a TSB for something similar. It does have to do with air in the system. I was looking at it a couple of weeks ago.

[WMX267]

Originally Posted by inafogg

when did this problem begin??was it ok before w/p replacement??it does sound like air
is traped in system.it could be a clogged radiator.with the engine @ operating temp
feel top & bottom of radiator they should be the same temp.if its ok try running with rad cap off to make sure air is out.if it starts over flowing gushing out radiator more than normal suspect a restricted/clogg in rad.whats the mileage

Sorry for the late reply. Yes, the problem started after replacing the waterpump. Mileage is about 217K. The top and bottom hoses don't seem to have the same temp @ normal operating temp. The lower hose is cooler.

You mean when burping, the coolant shouldn't be gushing out? When I was burping it, if I just let it idle, the coolant would start to overflow. One time I tried to rev the engine while filling the rad with coolant because it gets sucked in, when I released the throttle, the coolant gushed out like a geyser.

What do you think i should do next? How do I best deal with a clogged rad as you have suggested?

[inafogg]

why was the w/p replaced??because it was overheating? or was it leaking?
if rad is restricted/clogged your better off replacing it not too much $$$
you could have it checked(flow tested)rad shop can check it out of truck
it depends on was the w/p bad or we thought it was o/h because of a bad
w/p & relaced it.

[WMX267]

Originally Posted by inafogg

why was the w/p replaced??because it was overheating? or was it leaking?
if rad is restricted/clogged your better off replacing it not too much $$$
you could have it checked(flow tested)rad shop can check it out of truck
it depends on was the w/p bad or we thought it was o/h because of a bad
w/p & relaced it.

The explorer was not overheating. The shaft of the w/p had given out and rattles. But even with that, my temperature was nailed on normal, until I replaced the w/p.

Everything that has to do with the temperature of the ford was fine until I replaced that w/p. So it dazzles me as to why it would develop more problems after fixing one thing. BTW, the TSTAT is new as well.

[inafogg]

ok now im thinking air in system.have you checked for any ser. bullitin there may
be a certain way to bleed the system.hopefully scooby comes back with that info
are you just running with cap off to bleed??keep an eye on the the level in the
resivour.Good Luck Mike

[WMX267]

Originally Posted by inafogg

ok now im thinking air in system.have you checked for any ser. bullitin there may
be a certain way to bleed the system.hopefully scooby comes back with that info
are you just running with cap off to bleed??keep an eye on the the level in the
resivour.Good Luck Mike

Yup. I just let it run with the rad cap off and make sure coolant levels are good. Should I be revving the engine when bleeding? I did this one time and of course, the coolant in the rad goes down. I fill it up while holding the rpm, but when I release the throttle, the coolant shoots out. This is normal?

When it gets warmer, I'll try back flushing the heater core because the thumping sound does seem to come from the core area.

There was a TSB I saw about installing a coolant bypass kit to remedy. Symptoms are exactly what I am experiencing, but I'm having second thoughts about this - whether it would actually work as I would have to make another purchase.

[inafogg]

yeah if you rev engine water should go down & over flow when released if you added
coolant.but not shoot out just over flow.if it is then you may have other issues that thumping noise....does it start to dump coolant into the resivour when this happens & you turn engine off??? mike

[WMX267]

Originally Posted by inafogg

yeah if you rev engine water should go down & over flow when released if you added
coolant.but not shoot out just over flow.if it is then you may have other issues that thumping noise....does it start to dump coolant into the resivour when this happens & you turn engine off??? mike

Hmmm.... I see... by shoot out I mean geyser like. Plus, I don't know if you've read up in the post (no time to browse back), but when I rev the engine, the uppper and lower hose are squeezed, presumably by the suction of the w/p. this does not happen when the problem "is not present". I say this because it's intermittent.

[mechhound]

I suspect your new thermostat is defective and not opening(yes it happens). I would try another new thermostat. As far as burping the system, I would fill the block with coolant through the thermostat opening BEFORE installing the thermostat. Then fill the rest of the system with coolant before starting the engine.

Another good way of burping the system is to remove a heater hose by the motor, then add coolant as normal, the coolant will usually come shooting out the opening. This may not be possible on your vehicle as the heater hoses may be crimped on .

Just my suggestions.

[WMX267]

Originally Posted by mechhound

I suspect your new thermostat is defective and not opening(yes it happens). I would try another new thermostat. As far as burping the system, I would fill the block with coolant through the thermostat opening BEFORE installing the thermostat. Then fill the rest of the system with coolant before starting the engine.

Another good way of burping the system is to remove a heater hose by the motor, then add coolant as normal, the coolant will usually come shooting out the opening. This may not be possible on your vehicle as the heater hoses may be crimped on .

Just my suggestions.

Regarding the TSTAT, I wonder whether it could be defective because I don't overheat. My gauge would go never reach more than 55% of the gauge range, assuming 50% is normal driving temp. How can a faulty TSTAT explain the thumping sound?

Is there a quick way to determine intake and return hoses of the heater core?