[240] Another temp gauge weirdness...

[clay]

A while back I replaced the Timing belt, water pump, etc., and broken
temp sender.
When the motor is fully warmed, the gauge points about a needle width
below the red hot zone.

Put a new thermostat in it. Same thing.

The gauge showed normal temps (9:00) before the sender broke.

I've poked around the motor with an infrared thermometer.
Thermostat housing, block side near sender, head, etc. Nothing more than
165-170°F.
Top hose is not firm like I would expect if it were really hot.
Doesn't steam, boil, or smell hot.

So what do you think? The wrong sender? Bad replacement sender? Gauge
got trashed by the broken sender? I'm baking my motor?

I know the later cars had a circuit to normalize the temp reading that
sometimes goes bonkers. If my googlings are correct, this year didn't
have that.

What resistance should the sender read when it's working? Maybe I can
put a meter on it and see if it's telling the truth.

(1983 245)

 

[James Sweet]

A while back I replaced the Timing belt, water pump, etc., and broken
temp sender.
When the motor is fully warmed, the gauge points about a needle width
below the red hot zone.

Put a new thermostat in it. Same thing.

The gauge showed normal temps (9:00) before the sender broke.

I've poked around the motor with an infrared thermometer.
Thermostat housing, block side near sender, head, etc. Nothing more than
165-170°F.
Top hose is not firm like I would expect if it were really hot.
Doesn't steam, boil, or smell hot.

So what do you think? The wrong sender? Bad replacement sender? Gauge
got trashed by the broken sender? I'm baking my motor?

I know the later cars had a circuit to normalize the temp reading that
sometimes goes bonkers. If my googlings are correct, this year didn't
have that.

What resistance should the sender read when it's working? Maybe I can
put a meter on it and see if it's telling the truth.

(1983 245)

Probably the wrong sender, there are several different ones, and often
two different ones on the same engine. One for the gauge and a different
one for the engine computer. Dunno what the resistance should be off
hand though.

 

[clay]

Probably the wrong sender, there are several different ones, and often
two different ones on the same engine. One for the gauge and a different
one for the engine computer. Dunno what the resistance should be off
hand though.

That was my first thought. Double checking iPd, they only listed one.
That's the one I bought.
Maybe they got it wrong...

460191 Engine Temperature Sender
Engine Temperature Sender
Part#: 460191
Fitment: This is the sending unit for the engine temperature gauge in
the instrument cluster

I bet I have an old mechanical gauge/sender laying around from my racing
days. Maybe it'll fit and I can get a true reading.

Forgot to mention, also replaced the fan clutch. The old one freewheeled
when I turned off the motor... not pushing much air that way. *g*

 

[James Sweet]

That was my first thought. Double checking iPd, they only listed one.
That's the one I bought.
Maybe they got it wrong...

460191 Engine Temperature Sender
Engine Temperature Sender
Part#: 460191
Fitment: This is the sending unit for the engine temperature gauge in
the instrument cluster

I bet I have an old mechanical gauge/sender laying around from my racing
days. Maybe it'll fit and I can get a true reading.

Forgot to mention, also replaced the fan clutch. The old one freewheeled
when I turned off the motor... not pushing much air that way. *g*

Well they're supposed to freewheel when the radiator temperature drops,
but usually they have enough friction that they won't spin much.

You might have a bad gauge, or the wiring to the sender. There's a
voltage regulator on the instrument cluster but it also controls the
fuel gauge.

 

[clay]

Well they're supposed to freewheel when the radiator temperature drops,...

Usually a couple times around after turning off the motor.

I had driven 30 miles so it was warm. Just happened to lift the hood to
check something while it was still running. Reached in and clicked it
off. Fan was still spinning when I got back around to the front of the
car...

You might have a bad gauge, or the wiring to the sender.

After I replaced the thermostat, the motor warmed quicker. The gauge
marches up to it's too warm spot consistently.
That would imply the gauge is gauging something.
The manual says grounding the sender wire and observe the gauge reads
hot is the test for it. (why haven't I tried that yet?)
Also says don't leave it grounded too long.
When the sender broke the wire might have got up against the block or
manifold.
It was hanging out in space when I spotted the broken sender so I don't
think so.

There's a

voltage regulator on the instrument cluster but it also controls the
fuel gauge.

That's not the temperature compensator board is it? Thought I read
somewhere those didn't come along until 1985.

Interesting idea though.
I always check the gauges when I start the car... make sure they get off
their stops.
Recently, I've caught the fuel gauge climbing it's way up from empty as
I'm a couple turns into my trip home from work.
It wasn't that low when I drove off.
Only happened once or twice, that I noticed.

 

[James Sweet]

That's not the temperature compensator board is it? Thought I read
somewhere those didn't come along until 1985.

Interesting idea though.
I always check the gauges when I start the car... make sure they get off
their stops.
Recently, I've caught the fuel gauge climbing it's way up from empty as
I'm a couple turns into my trip home from work.
It wasn't that low when I drove off.
Only happened once or twice, that I noticed.

No it's a separate thing. On the later cars (early 80s?) it's a small 3
terminal device that looks somewhat like a power transistor, while the
earlier cars have a metal box about an inch long by half an inch square
that plugs in with two terminals on the back of the cluster. I've never
actually measured to see what the voltage ought to be.