Thread: Baffling 1988 RRC EFI 3.5 / oil pressure, temp gauge / Suspect "Voltage Stabiliser"?

Baffling me with something, perhaps this crew can help. 1988 RRC 3.5 EFI Hotwire, about 150K miles (US model), new to me (6 weeks). After a few weeks of going round and round, I'm now suspecting my oil pressure light, and temp gauge are giving me incorrect info. Fuel gauge is a bit all over the road too.

Here's what's I've done:

- When I got truck, temp gauge stayed very low (a nice change from my Disco 2 but no good). I changed out thermostat and did the coolant hoses and clamps at the same time as preventative. Cooling system in good shape, no sediment, radiator good.
- Replaced the temp gauge sender too since I broke off the tab.
- Had trouble bleeding system. Replaced Thermostat again, replaced the hard metal heater pipes with the new style with the fill pipe.. Seems to burp properly but still runs at 7/8+ on the temp gauge when warm.
- Oil pressure light flickered a bit when I bought the RRC. Changed out a cheap oil filter for Genuine Rover oil filter, replaced oil pressure sender, replaced oil with 20W-50 (thicker). Now it's worse - oil light flickers / comes on more than not at idle when warm. Also at times I notice there is no oil light on startup bulb check. If I fiddle with the circuit board behind the cluster with the cover off, it lights up. Dodgy something back there.

The temp gauge moves up in 10 mins to just below red. And the oil pressure light comes on after a few mins of running, at idle after a bit of revving. I've bled coolant system tons and think the air is out.

So swapped the oil pressure sending unit for a pressure gauge. Oil pressure doesn't dip below 20psi at hot idle. So that's fine, whew. Then used the infrared temperature gun, and when the car gauge shows it's overheating (almost at the red), temps on the engine, top of radiator hose, and everywhere are no more than 195-199 degrees F. Which is spot on.

Truck seems to run very well other than this, all new ignition components, smooth idle, good power. Ie there's no noise or smoke or coolant loss that would indicate to me the motor's been toasted and run with low oil pressure and a bum head gasket.

I was thinking both of these instruments (oil pressure lamp and temp gauge) operate off some ground / resistance theory. I read about something on the back of the instrument cluster called a voltage stabilizer. Anyone ever had this go bad? Could I be chasing down issues that don't exist?

It's a metal box above the tachometer, on the rear. Top right of this photo. Could this cause incorrect readings of oil pressure lamp, temp gauge and fuel gauge I think I'm getting? I have no idea where to score a new one. Apparently it is supposed to keep voltage at 10v solid for these gauges/indicators, and if it acts up, the gauges may not read correct.

Rear-88Cluster.jpg

Originally Posted by Homestar

Had similar with mine - bad earths. I ran a whole new one from the instrument cluster to a known good earth near the battery (a large brass bus bar I installed)

Fixed the temp gauge and fuel sender issues, although my oil pressure light was never an issue.

Try a temp wire from the cluster negative to the battery negative and see if this fixes it - if it does, run it permanently.

As Gav says, don't waste your time looking for the fault in the original wiring because you'll only find it by accident........ as in bumping a wire.

I learnt about the earth thing years ago with an XW Fairmont wagon with a 302 Windsor. Always ran slightly warm on the gauge, drove me nuts with thermostats, etc, etc. Even had a custom 3 row rad made which changed nothing.

Then one day I was replacing a globe in the dash and bumped a wire............ and the temp sat on just over 1/4 ever after.

cheers, DL