Very strange Cooling/overheat issue...

[pj8847]

OK, Maybe some here can give me a few ideas, because this is a strange one...

My '95 XLT with the OHV 4.0 runs like a top, no problems at all. I noticed though as the cold weather set in and I started using my heat, that when the heater is on, I get great heat, but, the temp gage will fluctuate from the cold point all the way up to the hot line (not the red line, the highest white line, and it hasn't gotten hot enough to trigger the "check gage" light). It will sit fine, but as soon as it starts moving up, it goes up quickly, and sits on the high line for a few seconds, then drops all the way down again just as fast. (small noticeable difference in heat output, but there is a difference).

Now with the heat off, my temp is stable throughout the range and doesn't move from dead center no matter how much load I place on the engine trying to heat it up. ( I can see when the t-stat opens and closes, the gage does move a tiny bit, but not much at all)

I've somewhat ruled out T-stat, since it's obviously working, and the Rad. Cap (it's a new 16lb "lever vent" unit). I have "burped" the system to no end, but there could be some air in there. I do however, notice a very strange occurrence when the heater is on as well.

When the t-stat opens, there is a massive amount of suction in the system that causes the top hose to collapse (top hose is in good shape, but it may need replacement), if I open the radiator cap at this point, I can hear air rushing in, and the coolant level has dropped enough I can add almost half to 3/4 a liter of coolant, but as soon as the t-stat closes, the extra I added in will just come shooting back out of the radiator unless I pop the cap back on quickly. this doesn't happen with the heater off...

I'm not burning coolant, no steam from exhaust. I DID have a small leak from my top hose clamp (cheap ford clamps, get loose after heat cycling and expansion/contraction, allowing coolant to seep past and leak out) but I fixed that, and I don't have any combustion gases getting into the coolant.

So I've ruled out the WP (since it's obviously got circulation) head gaskets and/or cracked heads as well.

I'm stumped, I'm thinking that maybe there is a possibility that the T-stat isn't opening or closing all the way, but why would me using the heater change how anything behaves? I now the heater core is clear, and the valve is actually working. Fan clutch is also working properly.

Would love some opinions on this, because when the gage goes to hot, the RPM's raise until it drops back down, which is as I said, within seconds, So it's not only the gage sensor that sees the temp increase, but the one for the PCM as well. Which rules out faulty sender, bad wiring, etc...

HELP! I've just about checked/done everything I can aside from tearing down the engine to figure this out...

 

[1AJeremyD]

Sounds like there might be a blockage in the heater core. Try doing a flush and get all sediments out and go from there.

 

[my98nnj]

Ummm if your 95 is a closed system, then the Lever Vent cap is the wrong cap.

You need a cap that works with a closed system.

 

[pj8847]

Sounds like there might be a blockage in the heater core. Try doing a flush and get all sediments out and go from there.

Heater core is clear. Tested flow through it with pressurized water, even back flowed it to get whatever "gunk' out that may have been stuck, but not much came out. My heat is phenomenal in the truck, if the core was blocked, I'd see an issue with heat, not with truck near overheating only when heater is on. Like I said, this one is making me insane.. I'm at a loss to figure out why it's doing this.

Ummm if your 95 is a closed system, then the Lever Vent cap is the wrong cap.

You need a cap that works with a closed system.

Not sure what you're talking about, or where you have gotten that information from, but that would be wrong. As I said, my cap is a NEW 16lb "Lev-R-Vent" unit, the one's with the red handle that allow you to vent pressure before opening them up...

It's the proper cap, seeing it's what has been ran on the truck since it was new. Matter of fact, I've always run these caps on all my vehicles, without a problem... Not sure what kind of cooling system you're thinking of (might be thinking of 1970 and earlier vehicles WITHOUT reclamation reservoirs or "catch cans", but as far as I know, these caps are made for EVERY vehicle on the market, regardless if it's open or closed (without/with respectively) reservoirs... that is the ONLY difference in the systems... cap wouldn't make a difference unless it was a completely different cooling system that requires a ZERO pressure cap (which many OLD pre 1940) vehicles ran, and they just puked out their coolant on the ground if it got hot enough, just like later cars without the coolant reclaimation/recovery tanks...

 

[ahodges]

I replied to the other thread you've posted in too and after reading your explaination, That is exactly the problem I had. I just started doing it out of the blue one day on a long trip! I replaced everything with no different results.. I gave up and took to a dealer I trust cause I know the guys there and they couldn't even figure it out. They replaced everything again including the thermostat, temp sending unit, fan clutch, and pressure tested the water pump which checked out fine. They then found a service bulletin about this problem and decided to order a special water pump the bulletin suggested. For whatever reason after that it has been back to normal and not a problem since.

The part number is: 97TM-8505-AC

Now before anyone goes saying I got ripped off or that this is a line of crap.. Let me tell you after they had it for a week they only charged me $400! The water pump alone retails for $200. Then add in a new fan clutch, thermostat, and sending unit which puts you over $400 in parts alone.

 

[pj8847]

The pump appears to be fine. It's circulating coolant with no problems. I already had the issue with the notorious "steam thump" a while ago, and had replaced the pump for that reason with the "expensive" one from ford (I didn't pay anything near what ford wants, under $80 thanks to my history with a local dealer)... it fixed the issue then, but the pump failed miserably some time later, wizzing out the weep hole and the shaft moved about on its bearings...real crap pump for what it cost.

I found an alternative part no. that was a direct cross reference to the ford part, from a manufacturer that cost only $40, and it flowed just as well if not better than the ford TSB unit. Part No. is - GMB 125-1770.
Its been absolutely fine ever since, until I noticed the gage doing it's thing...

Maybe the pump is getting weak, but from what I can tell, it's working as it should. Turning the heater on shouldn't cause the truck to run hot, it should do the opposite, since the heater core is removing heat from the coolant...
I would understand if it was doing this with the heater off, but the temp is rock steady with it off, and that is regardless of engine load/rpm...
This is why I'm stumped, and I've solved much more complicated issues than this in my 25+ years in the auto repair industry...

 

[ahodges]

oh ok.. Well idk about that issue then. It sounds the same as mine cause your top hose is collapsing just like mine did and everything. You realize i'm sure that there should never be vacumm on the top hose either.. so with that being said, there is deffinately air getting in the system some how.

That sucks about that pump though. I've been running mine now for 30k with no problems. My experience with cheaper aftermarket parts though is that they are "cheaper" and either fail soon than the OEM or don't work as good from the beginning. I've experienced this many times. That really puzzles me about your pump. You should have taken it back to the dealer.

 

[windsors03cobra]

Those Lev-R-Vent caps are good I agree but it sounds like you've got a bad headgasket to me.

 

[pj8847]

...your top hose is collapsing just like mine did and everything. You realize I'm sure that there should never be vacuum on the top hose either...

There will be some on the complete closing of the t-stat on a motor at operating temp... the pump is still sucking up coolant from the bottom hose at all times, and when the t-stat shuts, it cuts off any flow into the radiator, creating a suction, which is usually when the cap allows coolant to be recovered from the reservoir. If the suction of the pump is much greater than the flow coming in from the res, then the top hose can (if it is questionable, as mine may be a bit softer than it should) collapse for a brief time. This also happens if the pressure cap is failing and won't let coolant back in... I thought i had a defective cap at first, but its working fine.

Those Lev-R-Vent caps are good I agree but it sounds like you've got a bad headgasket to me.

I agree, best invention ever, prevents many cases of burns and blindness... As far as having a bad head gasket... a bad head gasket would cause the issue at all time during running operation. this is only happening while the heater is on. Again, I have no coolant loss, no combustion gasses in coolant, no coolant in oil, no oil in coolant... as I said, the engine runs like a top..no miss-fires, no fouling of plugs, no trace of any issues with heads/head gaskets. This is why I'm at a loss...

I'm thinking I may have an intermittent issue with the t-stat, and possibly the fan...I did notice it (the fan) may be pulling way to much air for it being so cold out ( I was outside investigating some more )... add the heater core cooling the coolant off as well when the heater is on, and I may be shocking (confusing) the t-stat into closing to soon, allowing the coolant behind it to heat up to a point where the t-stat has to snap back open and allows the coolant to flow... because there is an ever so slight pause when the gage shoots up, it hits halfway, stops for less than a second, the continues up until it almost hits the line, hovers there for a few seconds, and then drops way back down to the cold mark and stays there for quite a while. As soon as I shut the heat off, the temp will rise to mid point on the gage, and stay there... unless I turn the heat back on...

This is obviously going to drive me nuts for a while I see...

 

[gm558]

pj8847,
My '96 is doing the exact same thing. This started after installation of new heads (not rebuilt) and a new aftermarket water pump (done for mileage reasons). I have switched thermostats (no difference), and am in the process of reassembling the top end after a check on the new heads and gaskets. All were good and properly installed. My X has a new radiator, heater core, and hoses. I'll post any findings in a few days.

 

[TOMANDPAT]

This is a long shot, but how about a clogged hose between the radiator and the coolant reservoir?? Just thinkin' out loud

Tom

 

[gm558]

Good thought Tom, I'll check it tomorrow and post.

 

[lounge lizard]

does anyone have the original water pump that was in the motor before it was changed out and this issue started?

measure the flutes on the impeller for degree of angle and length of impeller blade.

a friend change a water pump in his car and he noticed that the impellers were at a different angle than the factory pump and that the impeller blades were not as long.

the result is he has temp gauge moves as if the T stat is opening and closing and he is seeing it on the gauge.

just a thought!

 

[swetrid]

Here was Fords old tsb.
Printable View (4 KB)
TSB
97-18-9 COOLING SYSTEM - TEMPERATURE GAUGE FLUCTUATION - VEHICLES WITH 4.0L ENGINE
NOISE - "THUMPING" HEARD FROM WATER PUMP AREA - VEHICLES WITH 4.0L ENGINE

Publication Date: SEPTEMBER 2, 1997

LIGHT TRUCK: 1994-1997 AEROSTAR, EXPLORER, RANGER


ISSUE:
A "thumping" noise or temperature gauge fluctuation may occur on some vehicles. This may be caused by the water pump delivering an uneven flow throughout the engine.

ACTION:
Replace water pump and gasket with revised Water Pump (F7PZ-8501-AA) and Gasket (FOTZ-8507-A). Refer to the appropriate year Aerostar/Ranger/Explorer Service Manual, Section 03-03, for water pump replacement procedure.


PART NUMBER PART NAME
FOTZ-8507-A Water Pump Gasket
F7PZ-8501-AA Water Pump


OTHER APPLICABLE ARTICLES:
NONE

WARRANTY STATUS:
Eligible Under The Provisions Of Bumper To Bumper Warranty Coverage

OPERATION DESCRIPTION TIME
971809A Replace Water Pump And Gasket - Ranger And Explorer 1.3 Hrs.
971809B Replace Water Pump And Gasket - Aerostar 2.1 Hrs.

DEALER CODING
BASIC PART NO. CONDITION CODE
8501 42

OASIS CODES:
204000, 204200, 402000, 497000, 702100


--------------------------------------------------------------------------------

Copyright © 1997 Ford Motor Company

 

[pj8847]

At this point I'm at a loss for why this is happening. It really just doesn't make any sense that the coolant temp. is fluctuating that wildly only with the heater on. I could understand if it were all the time, then I at least would have a start point to work with. Since it is only with the heater on though, I'd just be throwing parts at it to figure out what it is....

I've just about gone over everything, Rad, WP, T-stat, hoses, htr core, sensors, wiring, head & intake gaskets, no loss of coolant, coolant doesn't boil over, etc... and have found nothing wrong. I'm at the point that I figure, the truck is a '95, she is getting old, and I really don't want to bother sinking more money into it anymore, So I'm going to just run it like this. It's not overheating, it's close, but it's only with the heater on, and I get such good heat in the truck that I only need it on for a few mins at a time to keep the interior warmed up if needed. Otherwise, the temp is solid with the heat off.

Time may be coming up to put this truck to rest though... If anything turns up thats related or interesting, I'll post it up, but at this point, I'm done chasing this gremlin...

 

[gm558]

Done chasing myself I think. Mine is doing exactly the same thing. I did replace the water pump with a new one that looked the same as far as curvature of the impeler and diameter, etc. I am going to drive it and see.