Temp Gauge Giving False Readings

[Chirpstr]

Hi all, I'm currently getting erratic temp reading from my VR Berlina with the lev 3 dash (standard). It goes up to the hot mark even when the motor is fairly cold. It's electrical, but the thing is I have already replaced the coolant temp sensor and also the coolant temp sender...both being brand spankers. Maybe bad earth but wiring seems to be all good.

I'm really stuck with ideas here...Any rough thoughts that you guys could throw out would help a heap.

Cheers.

[Ron41]

sorry, stuffed up.

[Ron41]

sorry again, don't know how to delete message

[Ron41]

I just changed my temp guage because of very high readings, brought it back down to 3/4 mark before the low fan kicks in.
I got a price for a new one it was $170, plus $100 to fit it at an auto electricians, so I finished up getting one from the wreckers for $22, easy to put in, this will help if you need it.
Broken Odometer

Rony

[Cheap6]

It possibly is the gauge or in the instrument cluster assembly, especially as the sender has been replaced. You be able to find info. about dry solder joints in the instrument cluster printed circuit board if you are willing to brave a search. There are also a couple of nuts that hold the gauge in place and also provide the electrical connection to the PCB that are worth checking (for good electrical contact).

To check the gauge operation, unplug the sender and earth the wire through the engine (manifold) via a resistor (<$2 from Jaycar/Altronics/DS). 283 ohms is cold, middle is 56-68 ohms, hot is 36-44 ohms (all V6 - VP but VS will be the same).

[Chirpstr]

Ok an update. I pulled dash to bits checked for dry joints and check the temp gauge and seemed to be all good. I checked the plug on the temp sender again but still doing the same thing. I remember since I plugged in my vp trip computer part to the 4th plug just to check the led's were ok that I changed it started from here but I think its a coincidence.

Cheap6, what type of resistor do I get? Can I do it with a multimeter some how? Think this is the only thing to check now.

Cheers.

[Cheap6]

The type of resistor doesn't matter much but with 40R the power dissipated will be ~2.5W (10V/40R=0.25Amps, 0.25AX10V=2.5W) i.e. the resistor will get hot (and eventually die) if it's rated less than that and you leave it connected for very long.

Try 5W 5% wirewound.

Jaycar:

270R, RR-3284

56R, RR-3286

39R, RR-3264

@ $0.40/

You can use a multimeter (voltmeter) to verify that there is 10V (reg'd from battery voltage) at the plug to the sender on the manifold. If it's not 10V there, work back by checking @ the gauge - you will have seen the labels on the plastic PCB and be able to trace the circuit back further on the PCB if required.

[Chirpstr]

I swapped the temp gauge over with another good known working one but still doing the same...I have no idea now...It goes up to Hot when it warms up then back to just over the first line (normally always just under) and stays like this most of the time, although it does go back up to hot sometimes. I'm thinking the ECM has a problem but its a manual so very hard to find another or, it could be the wiring but it would go up and down over every bump...(recently went on some gravel).

[Cheap6]

What does the gauge do with the resistors connected in place of the sender? If it goes to cold, 1/2 and hot with the appropriate resistors, the gauge is OK.

Is there 10V on the wire to the gauge sender and if not, at the PCB (check with the terminal off the sender end - you can use jumper wires to keep the connections as required to check the PCB/cluster end)?

To check if the engine temp. is doing what the gauge says it is - that might be a PCM or CTS fault - what does the coolant temp. sensor voltage do?

For VT V6, which should be similar, it should start at ~2.5V (20C) and fall to ~1V (50C), then jump up to ~3.5V (51C) then fall to ~1.5-1.3V at operating temp. You should see the voltage fluctuate between ~1.5V and 1.3V as the fan cycles on and off.

Check it at the PCM terminals - check the colours at the sensor but I think the wires wiil be yellow for the signal wire and yellow/black trace for the earth.

You might also try recording and plotting (time vs voltage = time vs temp.) the voltage every 10 seconds or 20 seconds as the engine warms up.