Hey everyone,

I'm posting this for a friend of mine who is having problems with his '94 Aerostar:

"I'm seeing a problem with my van! The cooling system gauge never quite reaches top center. When it almost does, it starts dropping down to cold, then gradually climbs back up and does this all over again. Interestingly, the heater temps don't exactly correspond to the gauge. The ambient temperatures vary about two minutes behind what I see on the gauge.

I've heard of sticky thermostats, but this one is obviously not sticking open, or shut. What do you think could be the problem? I need to fix it before it gets too cold out."

I've heard that this could be a sign of the waterpump failing. True? The only problem I have ever had with my Aerostars is that on one of my '92s (the short one) the temp guage almost never moves. Thanks in advance!

 

This erratic behaviour is seen most frequently after flushing the cooling system due to trapped air. Low coolant levels will also give the same up/down fluctuations. First try checking the coolant level when the engine is cold. A full reservoir does not rule out low coolant as the line between reservoir and radiator may be plugged.

If the level is correct, then consider changing the thermostat. It is opening and closing but may be weak and doing so at too low of a temperature.

Water pumps are rarely at fault in these situations. It is also possible the problem lies with the temperature sending unit itself, but your post makes it seem like there is a correlation between gauge fluctuation and heater output. If this is true, then the sending unit is not the culprit.

 

I understand that this is normal behaiour. My gauge does this (perhaps to a lesser degree), too. All other cars with good-condition thermostats/gauges that I have driven also do this. It's an open/close system where when the fluid gets hot the thermostat opens up to allow circulation and then when it gets the cooler fluid hitting it again it begins to close until the thermostat until it fully closes and begins the cycle again and again. In the science world we call it an heuristic loop. Because cold and warm fluid are constantly mixing you don't get just one happy spot the thermostat stays at. That's precisely why it operates on the melting point of wax rather than some electronic valve. The electronics programming required to mimic such natural behaviour would be complex and require more sensors. That's not exactly what we need, is it? The physical properties of a thermostat are perfectly designed to meet this need.

 

I found the following TSB that mentions an erratic water temp gauge.





Printable View (4 KB)
Article No.
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: 1994-97 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

 

I've prayed that I would be more humble... I suppose this is one of those times My discertation stands corrected.

 

Well, I wasn't trying to 'correct" anyone.
I just found the info on my Ford Service DVD, as my '97 does the same thing.
No, I haven't changed the pump yet.
My question is, when one goes down to the local parts house and gets a rebuilt water pump is it the revised version or, as I assume, just a recycled old version.
I would think that if someone were having the wavy gauge problem and just went and got a rebuilt pump, the problem would still be there.
Of course, the 'genuine ford' part is probally rather costly, but if it stops the gauge from bouncing around it would be worth it.
Just for info, I had a 3.0 that started the wiggly gauge deal AFTER I changed the thermostat.
And I bought one of those 'premium priced' thermostats for my 4.0 and it didn't change a thing.

 

Oh, very interesting thread, I am thinking to check my temperature sending unit for my 1993 4.0 L engine because my temp gauge not work, it only works when I turn on the a/c system and the needle's temp gauge arrives at the top. Now, where is located the temperature sending unit?
I must verify its operation with digital multimeter?
Any info would be appreciated and
desire that dajazz solves its problem soon.

 

see http://www.cybrrpartspro.com/Chilton...24CH02_31.HTML
I would just replace it. It's a thermistor and they have a limited lifetime.

 

Thanks man.

 

well ford guages are mediocre at best. any mech will tell you that. any factory guage is subject to hilarious laughter. But on a more concerned note, I would say, over time, the radiator and heater core and passages as well as water pump and the temp sender all are subject to age and deterioration, so if you have a build up of corrosion in one place, you will have it in another, as well as reduced flow, giving you some pretty crazy readings. Short of replacing entire cooling system, the age old motto applies, if it aint broke, don't fix it. Do the normal maintenece stuff, as long as motor is keeping cool, and transmission fluid is getting proper cooling, and the heater is getting optimal, I would get a pressure test of the system, replace the radiator cap, make sure the bleed pin hole in the radiator neck is clear, along with the overflow tube, and just live with the flaky readings. I am sure it needs new cooling components, most vehicles do at some point, and when it needs radiator and fan clutch replacement, and heater core, and water pump, then fix it. you could spend alot of money chasing this, and it not be life threatning. I use synthetics and the high mileage dexcool (orange) coolant. I have very small flutter in my guage, but it has been for 90,000 miles. And everything checks out to be due to deterioration of cooling system in mine. I suspect once I change cooling components, all will be well with mine. I am sure this is true for most vehicles. PS. mine has heavy duty cooling and never has reached over the O in the NORMAL band on the guage.

 

I have a recently purchased 94 Aerostar shorty with about 104,000 miles. It has dual heat /ac. The temp guage bounces around between N/O and 0/R. On a recent road trip, (FL to IN) the check engine light was coming on when the guage swung low and would go off when the guage swung high. I don't see the check engine light when driving around town, only when driving on the interstate after 1-2 hours. I was thinking that the computer was getting confused by the varying temp settings. Also, the antifreeze was dirty, the overflow tank was empty, front heater didn't work very well but the rear heat was OK. It always seemed (smelled) like it was running rich as well.

It's at the mechanics now, and after a flush and new thermostat, it won't get over the O reading even with the radiator hose pinched off.

I'm guessing that maybe the 'stat is defective and /or there is still some air in the system.

Any other ideas what is causing the low readings?

Or maybe it has the "heavy duty" cooling system and that's as warm as it gets. What indicates a "heavy duty" system vs the standard one?

 

If you have secondary heating, you have heavy duty cooling already. O range is normal. Best of luck