Fake overheating?

[psdforever]

1999 LR Disco 1, 191,800 miles. New radiator, water pump, thermostat.

Temp gauge on dash creeps up to "H" red mark when at idle and A/C fan on number 4 setting. If I turn the fan switch to number 2, the dash gauge returns to normal range just below midpoint on the gauge within 2 to 3 seconds.

I put an ODB scanner on and monitored the coolant temp and it never went above 188 degrees even when the dash gauge was pegged at HOT. When I turn the fan switch to number 2 and the dash gauge returns to normal, the ODB readout stays solid at 188 degrees.

If I pull the dash coolant sensor wire off at the engine, the dash gauge goes to cold, putting it back on it reads the same as when it was pulled off.

Does this seem to be a bad coolant sensor for the dash gauge?

Any other diagnostics the group can think of so I don't throw parts at this? What would be a link between the fan switch on number 2 and on number 4?

Thanks in advance.

 

[ERover82]

Sounds like an electrical issue if real temp never exceeds 188 and it reads correctly on a certain fan setting. Does it do it while moving and/or AC off and fan on 4?

 

[psdforever]

Ok. Just Ohm'd out my coolant gauge sensor. Sensor reads 40.9 Ohms when A/C is on and fan switch at #2 and goes to 35.1 on fan switch at #4 with A/C on. Ohms should be around 300 for 185 degrees from another post. Again checked the ODB II data and rock solid at 187 degrees. Looks like I need to order a coolant sensor.

Agree?

 

[psdforever]

Erover, the dash gauge shows overheated whether I'm moving or not as long as the A/C is on. If I'm sitting still and turn the A/C off, the the dash guage returns to normal within about 2 or 3 seconds.

I think the coolant sensor may be shorting out when the engine temps get to normal range.

 

[Tugela]

For $20 is it worth a gamble on the sensor? That's the going price on AB to take the first example, you might find better.

 

[German Gruner]

You should check grounding point from "A" pillar. It is a nut fixing a terminal bloke with a lot of black cables. As this mass point may have electrical resistance, different devices connected make needles to turn.
Another important mass points are recommended to be checked. Or better said, you can loose nuts, spray some WD40 and retighten nuts.

Regards

 

[German Gruner]

See images from A pillar grounding point
http://www.landroverclub.com.ar/viewtopic.php?nomobile=1&f=20&t=99471

 

[discostew]

I agree it's a bad ground. Other circuits are probably effected.

 

[pdogg]

I went through that on my RRC.. old sensor.. cheap fix..

 

[AfiRover]

Common issue on D1 go check your alternator I know it sounds crazy but check it

 

[psdforever]

German, am I looking under the dash near the fuse block, or near the driver's kick panel for the grounds?

I had a little trouble identifying the grounding block in the pictures. Thanks for your help.

 

[psdforever]

Afi, am I checking the voltage output on the alternator, amps or both? I'll put my multi meter on it and test voltage tomorrow. I'd need to pull it and take it to NAPA to have them bench test for amps.

 

[German Gruner]

You must take drivers kick panel out. You will find there this big ground block.

Regards

 

[psdforever]

Just an update. Also agree electrical and probably a grounding issue. turning headlights on caused temp gauge to spike, turning off it went back to normal. Also noticed with headlights on when stepping on brakes while rolling to stop caused temp gauge to rise also. I could also see the backlighting of the temp gauge blinking in timing with the turn signal.

Guess I'll pull the driver's kick panel and check grounds.

Anyone have a list of where other grounds might be so I can check them also?

Thanks again. Getting it narrowed down.

 

[psdforever]

I did check the voltage of the alternator and it's putting out 14.04 volts. After shutting off the engine, battery voltage reads 13.32.

I may clean the battery terminals just for peace of mind.

 

[mgreenspan]

Check your engine block to chassis ground strap/earth strap/whatever you want to call it, too. I had this exact scenario in an old 110 that ended up being that main ground from the motor to the chassis.

 

[psdforever]

Just checked the battery connections, battery to frame, ground strap in driver's kick panel, and ground strap below driver's windshield wiper arm out near the firewall.

Did not try running it to get it hot, but I get a "pop" from the radio and it sometimes cuts out when switching the fan from off to #4 setting.

I will check the engine ground strap, any other grounding points under the dash? Any behind the radio maybe?

Just a thought, I did have the windsheild replaced about 2 months ago. Any connection with that?

 

[German Gruner]

Yes... just check for water ingress...
You may find white salt paths or rusty spots in places where water is frequently present
Regards

 

[psdforever]

Update:

Picked up a used alternator from pull and pay. Checked output voltage and getting 14.01 volts. Dash gauge pegged after driving 15 minutes to NAPA to pick up tail light bulb.

Had NAPA check the battery and alternator under load. With all I could turn on electrically, alternator puts out 13.86 volts. Battery checked out ok on Load test and CCA.

Installed new temp sensor from atlantic british this evening. Within about 5 minutes, ODB scanner shows coolant temp at 145 degrees and dash gauge pegged again.

The gauge is pegged when the heater fan is on #4 and the headlights are turned on.

Turning the fan switch off and headlight switch off makes the dash gauge go back to normal?

I'm about at my end with this. Any ideas?

I did not see any water infiltration from the windshield replacement. All looks dry.

 

[Icannap1]

Since you already replaced the temp switch I would unplug it and then turn on the rover the gauge should not be reading anything with the connector unplugged then turn on your heater fan and set it to #4 as this usually triggers your symptom it should not cause the temp gauge to spike if it does the problem will most likely be a pinched wire or an uninsulated wire that is used for the dash temp. You can use an ohm meter to check the connection from the sensor wire disconnected from the sensor and check for resistance and continuity to the other end at the gauge cluster C222 pin 8 GU (green/ blue). If continuity is good with no change due to moving your fan switch then undo the grounds in the kick panel and clean with a wire brush even if it looks good. The other thing you can do is get a jumper cable black end clip it to the negative terminal of the battery and clip the other end to the metal bracket between the power steering pump and motor. After placing black jumper cable to battery and motor ground go ahead and move the fan switch and see if the problem still exist if it doesn't then your engine ground is the problem remove it and clean area with a wire brush and reattach ground cable. I would also check to main ground cable and see if the grounding post behind the battery below the fuse box and coolant bottle is secure (clean it with a wire brush and reattach) and the end of the cable that attaches to the frame by the passenger wheel well (clean it with a wire brush and reattach).