This will stump the expert on a temp gauge.

[Mangler90]

I have 1990 Merc V-6 4.3 liter engine and can't get the temperature gauge to work. Here is what I have done:
- Replaced the guauge
- Replaced the hot wire to the gauge
- Replaced the thermostat.
- Replaced the sender.

So now what. I when I hook it up without the top of the thermostat cover on and poor hot water onto the sensor the gauge works but when it is all connected and the engine is running, there is not action in fact it looks dead. If I ground out the tip of the sensor it redlines, which I have read is a test of the gauge.

One odd item is when I turn on the key it seems to stick to the cold side almost the opposite of grounding it, when I turn off the key it climbs to about 140 deg. or about a third of the way up. I don't know if this is a clue to anything or not.

If you can solve this one you ARE the expert.

Thanks for any help

I

 

[Don S]

Re: This will stump the expert on a temp gauge.

Does the gauge itself have a good ground? You said you replaced the hot wire, but nothing about the ground.
Also check for continuity in the TAN wire from the sender to the gauge. (disconnect at both ends before testing)

One more test. With the ignition key in the run position (on) remove the wire from the sender and ground it on a good clean ground, The gauge should peg full hot.

 

[cr2k]

Re: This will stump the expert on a temp gauge.

Pull your thermostat housing, pull the thermo and all the hoses. Where the seawater enters the housing; that cavity feeds 2 passages, one you can see and one just around the corner you can't. One in to the big hose and one in to the thermo area. The one you can't see is still holding hostage a chunk of impeller of days past. (or scale/rust, debris)

DISCLAIMER: or not.

 

[HT32BSX115]

Re: This will stump the expert on a temp gauge.

One more test. With the ignition key in the run position (on) remove the wire from the sender and ground it on a good clean ground, The gauge should peg full hot.

And then one more test...

Take some sand paper and cleanup the grounded (threaded) part of the sender that screws into the block and touch a wire from it (while the wire is connected and it's still screwed into the housing) to the ground lug on the battery and see if the gage moves at all.

(it shouldn't if you do have a good ground......because it's already grounded!) If the gage DOES move, you probably have one or more bad ground connections.

 

[Mangler90]

Re: This will stump the expert on a temp gauge.

Okay here are answers to the responses

Don--I haven't tested the ground at the gauge, I assumed it was okay since all the gauge grounds are connected and the other gauges work, but I will still check it. I did make sure the outside of the sender (not where the hot wire attaches) is grounded. There isn't a ground for the sender, my assumption is the outside of it is grounded to the engine. The ohms resistance meter read .56.

There is continuity on the tan wire.

When I ground the hot wire from the sender and turn the key to on the gauge does peg full hot.

CRK --The pipes are clean, no impeller parts or other.

HT32BSX115 -_ I have did ground the sender from the battery and with no change in the gauge. The sender is well grounded.

Next steps?

 

[Bt Doctur]

Re: This will stump the expert on a temp gauge.

try running a temp ground wire from the neg battery to the Black main ground behind the dash

 

[Mangler90]

Re: This will stump the expert on a temp gauge.

I ran a temp wire from the battery neg to the ground behind the dash--the gauge still doesn't move.

I also tried running power directly to the gauge meaning a pos and neg from the battery to the gauge with the sender still intact and movement.

 

[cr2k]

Re: This will stump the expert on a temp gauge.

Some systems are possessed. Last year we had one. Ran new wires and everything it just would not work. Each piece worked perfect individually, but as a group they didn't pay together at all.

 

[fat fanny]

Re: This will stump the expert on a temp gauge.

As of today I thought I had my issue solve but! when I syarted after sitting for a while my temp guage read nada but as I excellerated it poped up to temp and when i decellerated it died and vise versa. @ that point it was gonna be part of a NE Ohio LeBron fire but I think after tommorow I have narrowedit down to a dead short in the neutral saftey switch I may be wrong but I have a ground out situation somewhere and when I sarted moving the throttle and the temp gauge inermitantly worked I looking there try it and post back

 

[rodbolt]

Re: This will stump the expert on a temp gauge.

its not uncommon for engines to never warm up on a flusher.
test it in the water under its normal load.

 

[dingdongs]

Re: This will stump the expert on a temp gauge.

try a hot cup of water and run an earthwire from your engine to earth on your sender and try sensor end of switch in the hot water.see if it registers any movement with your ignition switch on.may also try boiling in a saucepan your thermostat to see if it opens and at what temp.if these work can only assume no water is in the housing.