Hello Folks,

First I'd like to say I really enjoy and utilze this site. It has information on most everything I've needed to do to fix up my '85 Turbodiesel. One thing has come up though I am unclear on. On my car the gas gauge has quit working and the temperature gauge shoots into the red after a minute or less after getting juice. In the FAQ section it says that only cars up to 1984 have voltage stabilisers. However my late friend (a diesel mechanic who rebuilt EVERYTHING forward of the cowl), who I purchased it from, told me the erratic gauge behaviour was due to a "diode" in the "dash" that was going. Could the '85 td have this older design? Or is something else causing it?

As for everything else, the car runs well and strong. I live out in the country, so it doesn't seem the "stop and go" issue on this motor is much of a factor.

Thanks,
Dennis

Lets see here, your car is a 85 model year and that makes production in mid 84 or early 85 and this production would still use the thermal gauges meaning it also has the little 8 volt regulator on the back. It will be a black plastic sqaure with a thin bent tab sticking through the top and 3 leads at the bottom with the whole affair mounted to a sheet aluminum heat sink.
First order of business to troubleshoot. Using a VOM that is greater than 10k ohms/volt pull the connector from the temp sender off and connect the meter positive while grounding the meter negative. If you find +12 volts at this point its a bad regulator. If you find nothing switch to your ohms scale and measure resistance with the ignition ON. If you find under 3 ohms its shorted wiring. Now go to the back of the car and dig up the fuel sender wiring and do the same tests. Wires will be on the driver side under the wheel well padding and will be a 2 position connector piggybacked to another 2 position, this is because the diesel cars used 2 seperate tanks, one on top in the trunk and the other under the car... Why I have no idea!
The target voltage should be 8 volts +0.5/-0.5v and if either of the connectors are shorted for an extended period of time they will burn up the little thermal strip heater in the gauge, if the burned heater end should find a ground it will short out the voltage regulator and bring +12 to your gauges making them read very high all the time.

Little known fact of Volvo gauge clusters, the diesel cars carried over the old thermal style gauges until 1985 and they will not interchange at all with the newer style jeweled "balanced field" meters because the fuel sender reads low to high and the jewel gauge is looking for high to low for fuel full to empty. Also the tachometer is completly diffrent and uses the 'W' terminal on the alternators and a 2.5:1 pulley ratio to measure engine speed, using a gasoline 4/6 cyl tach will only pin the needle because the output will be several hundred hertz with the engine speed at 850 RPM. The alternators are 12 pole 3 phase delta connected and at the 'W' terminal the frequency is doubled as a result of the diode trio. The temp gauge however reads low to high regardless of design but the jeweled meter will not physically interchange into a thermal design gauge cluster housing.

Hope this helps shed some light.

Badge988
764GLE D24TIC

First, I wouldn't be so quick to lump these two issues into one problem. The gas gauges are notorious for being intermittent. Can you bang on the dash next to gas gauge and it starts working? That's in the FAQs also. There is a section under cooling in the FAQs that discusses odd acting temp gauge. I would work one issue at a time.