Erratic temp gauge

Mercutio

Mercutio

SCCoA Member
My coolant gauge is all over the place. It'll jump up or down quite a bit at a time--way more movement, and faster, than real coolant changes could cause. I've already tested a new gauge, and new gauge cluster. The problem definitely seems electronic. I'm thinking the coolant temp sensor is next--any other ideas?
 
Maybe double check the connection at the sensor first? Could a loose wire show erratic changes?
 
Connector at the sender behind the thermostat housing - remove, clean it and the post, squeeze lightly to tighten up the grip and push back on.

Must be tight and clean - no green corrosion. Replace if unable to clean.
 
Ahem.

TSB 95-13-2

07/03/95
^ GAUGE - TEMPERATURE-READS IN LOW RANGE - ERRATIC READINGS
^ SERVICE PARTS - RETURN OF OBSOLETE TEMPERATURE SENDERS
FORD:
1981-94 ESCORT
1981-95 MUSTANG, THUNDERBIRD
1983-95 CROWN VICTORIA
1984-94 TEMPO
1986-95 TAURUS
LINCOLN-MERCURY:
1981-92 TOWN CAR
1981-95 COUGAR
1983-95 GRAND MARQUIS
1984-92 MARK VII
1984-94 TOPAZ
1986-95 SABLE
1987-89 TRACER
1991-94 TRACER
1993-95 MARK VIII
LIGHT TRUCK:
1982-95 BRONCO
1983-95 RANGER
1986-94 AEROSTAR
1990-95 F-150-350 SERIES
1991-95 EXPLORER
1992-95 ECONOLINE
1995 WINDSTAR
ISSUE:
Temperature Sender F1SZ-10884-A with a build date code prior to 2774 (277th day of 1994) should be purged from your inventory and returned to your facing PDC. These parts are being made obsolete because of an incorrect crimp during assembly. Installing these parts on a vehicle could result in early loss of temperature sender function.
ACTION:
Remove and return the suspect parts from your dealership's inventory. The obsolete parts should be withdrawn from your inventory and returned to your facing PDC within 30 days of this TSB.
NOTE : USE TSB ARTICLE 93-24-8 FOR DIAGNOSIS PROCEDURE IN DETERMINING IF LOW GAUGE READINGS COULD BE ASSOCIATED WITH A TEMPERATURE SENDER CONCERN.
Click to expand...

Just FYI.

RwP
 
air pockets have been known to cause this. also a failing thermostat can cause this. fill the system with the vent port open. start and run for about 1 min, turn it off and refill the system. then run it up to operating temp and see if it continues to give bad readings. if it does then change out your thermostat. repeat the fill process. check at full operating temp.

also is your cooling fan turning on during this?

is there any over flow after shutting the engine off?

is there any leaking coolant after shutting off and/or letting the car sit over night?
 
Only time I've seen the temp gauge give erratic readings is when there was an air pocket. But I suppose a loose connection on the sender wire could also cause that.

David
 
KMT said:
Connector at the sender behind the thermostat housing - remove, clean it and the post, squeeze lightly to tighten up the grip and push back on.

Must be tight and clean - no green corrosion. Replace if unable to clean.
Click to expand...

Mine was dooing the same thing what KMT said fixed it
 
I never checked for air pockets just because my brain got into "must be electrical" mode and never deviated. I'll check it out this weekend. Thanks to all.
 
Don't forget, there was a recall on the sending unit on 1994 and earlier cars.

Check the date code as in the TSB I posted - if it's in the affected range, replace it.

I bought one for ... $10 IIRC ...from RockAuto with some other items I was ordering.

Just remember and get the RIGHT sending unit - on the 5.0 I have, there's three (!!!) that are there for temp reading, the Cold Engine Lock Out (CELO), the gauge sending unit, and the ECM sending unit.

RwP
 
I just checked for air pockets and there didn't appear to be any. So next to check is the coolant sensor. Dumb question, but it is the sensor just ahead of the coolant bleed screw on the t-stat housing, right? For the life of me I couldn't get the plug off the sensor, so before I break it I'll ask what I'm doing wrong.
 
Mercutio said:
I just checked for air pockets and there didn't appear to be any. So next to check is the coolant sensor. Dumb question, but it is the sensor just ahead of the coolant bleed screw on the t-stat housing, right? For the life of me I couldn't get the plug off the sensor, so before I break it I'll ask what I'm doing wrong.
Click to expand...

ON a 5.0?

Look over the water pump.

Look at the right, very front of the intake manifold.

Now move the wiring harness that runs around to the ignition coil, and look down below the right angle bend.

THERE is the coolant sensor.

RwP
 
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