Cycling temperature gauge

I had posted the following to an old thread, but it resides in Under The Hood, which is not really where this subject belongs these days, so I post here to get a little more visibility:

(the original thread is Dead Link Removed )

Doing a lot of searches to see if there is a definitive answer to this issue. From this and other threads, seems like it could be any of several things:

1. Bad thermostat
2. Air bubble
3. Bad radiator cap
4. Clogged radiator
5. Bad water pump
6. Bad fan clutch
7. Loose wires
8. Head gasket leak
9. ....what else...?

I just noticed mine doing this flucuation recently. Did a 60k service just a couple months ago, where I flushed coolant and changed t-stat and rad cap.

Then, on Thanksgiving, got a chirp when I started the car that my brother said sounded a lot like when his water pump in his SHO started to go bad. And I think I caught a whiff of coolant after I parked the X. Haven't crawled under yet to see if the weep hole is weeping.

So my problem may be a water pump starting to go. I will post after I replace it and let this thread know if it helped the gauge problem. I'll not do the tstat and rad cap again right at first, so I can tell for sure if the H2O pump did the trick.

Did you see this thread?

Dead Link Removed

This would eliminate one of the items on your list.

Im also wondering if installing the thermostat in the wrong position (the small hole should point up) might cause this issue.

Also, there are a couple of TSB's related to this:

Cooling System - Thump Noise/Gauge Fluctuation
Article No.
97-18-9

09/02/97
^ COOLING SYSTEM - TEMPERATURE GAUGE FLUCTUATION - VEHICLES WITH 4.0L ENGINE

^ NOISE - "THUMPING" HEARD FROM WATER PUMP AREA - VEHICLES WITH 4.0L ENGINE

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

F0TZ-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 1.3 Hrs.
Gasket - Ranger And Explorer

971809B Replace Water Pump And 2.1 Hrs.
Gasket - Aerostar

DEALER CODING
CONDITION
BASIC PART NO. CODE
8501 42

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


and

Cooling System - Erratic Temperature Gauge/Noise
Article No.
99-23-8

11/15/99
^ GAUGE - TEMPERATURE GAUGE FLUCTUATION
AND/OR "KNOCKING/THUMPING" NOISE FROM
COOLING SYSTEM - 4.0L OHV ENGINE

^ COOLING SYSTEM - PULSATING COOLANT
FLOW - NOISE - "KNOCKING/THUMPING"-
AUDIBLE IN PASSENGER COMPARTMENT - 4.0L
OHV ENGINE

^ NOISE - "KNOCKING/THUMPING" - COOLING
SYSTEM - AUDIBLE IN PASSENGER
COMPARTMENT - 4.0L OHV ENGINE

FORD:
1995-2000 EXPLORER, RANGER

This TSB article is being republished in its entirety to include 2000 model year vehicles and to provide Service Part(s) and Labor Time information.
ISSUE
A temperature gauge fluctuation and/or a "knocking/thumping" noise may be audible in the passenger compartment on some vehicles. This noise is most pronounced with the engine at normal operating temperature. The noise is caused by steam formation in the cooling system. The noise is then transmitted through the heater hoses and heater core.

ACTION
Install a Coolant By-Pass Kit. This increases coolant flow which reduces steam formation. Refer to the following Diagnostic and Service Procedure for details.

DIAGNOSTIC AND SERVICE PROCEDURE
1. Check for excessive exhaust system restrictions. A restricted exhaust could elevate cooling system temperatures.

2. If dash-mounted cooling temperature gauge fluctuates, check that gauge and sending unit are functioning properly.

3. Check for restrictions or kinks in the radiator or heater hoses.

4. Pressure check cooling system for leaks.

5. Confirm proper Engine Coolant Temperature (ECT) sensor signal to EEC-V processor.

6. Check for correct 50/50 coolant mix. Verify that freezing point is -37°C (+/- 15°C) or -35°F (+/- 5°F).
edit:
7. If concern still exists, install service Coolant By-Pass Kit and verify that concern has been resolved. Refer to the Application Chart in this article.

PART NUMBER PART NAME

F8PZ-8522-AA Coolant By-Pass kit
F8PZ-8522-BA Coolant By-Pass Kit
F8PZ-8522-CA Coolant By-Pass Kit

OTHER APPLICABLE ARTICLES: 97-18-9

SUPERSEDES: 99-7-2

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

OPERATION DESCRIPTION TIME

992308A Install Service Coolant 0.7 Hr
By-Pass Kit

992308B For Diagnostics, Use "A"
Time Per The Warranty
And Policy Manual


DEALER CODING

CONDITION
BASIC PART NO. CODE
8522 42



OASIS CODES: 204000, 204200, 208000, 402000, 497000, 702000, 702100, 702300


Sorry for long post.

Thanks for the "long" reply. Yeah, I think I did a good job of burping the system. Given the other symptoms with my water pump, I'm hoping that's it. But I'm gonna take it one at a time...

Thanks for the TSB's, too. I was wondering what they had to say. I'm not hearing the thumping noise, but it's good to know there's an updated pump.

Man, I'm having the same problem. One day, out of the blue, the temp guage started Fluctuating. I've done everything I can think of:

Fan and Clutch
New Radiator
All New Hoses
New T-stat (done this twice)
New Radiator Cap
New Temp Sending unit (for the guage)
New Water-Pump (today)


Still doing it! I'm going nuts! I'm gonna get the system flushed in a few days, and pray that that works. I don't know what else to do...

new water pump solved my problem. some others have taken the 12 o'clock bleed valve off of their thermostats to keep the needle in a more consistent position. let us know what works for you.

Originally posted by rossneag
some others have taken the 12 o'clock bleed valve off of their thermostats to keep the needle in a more consistent position.

Click to expand...

Did they plug the little hole ? Or something else?

NO, they left it open so more coolant travels through it. It takes a just a little longer for the engine to warm but keeps the needle stable.