I bypassed my temperature compensation board yesterday. It was very easy, only took about 30 minutes including pulling and reinstalling the instrument cluster. Unfortunately, my temperature guage is still wandering into the hot region and giving me quite a scare just as it did before the bypass. Anyway, since I seem to be taking much more than I'm giving to this forum I thought I'd post some pictures to help other owners who want to make this modification.

Instructions are this simple.

1. Pull the instrument cluster and remember to write down which wire connect where. It is amazing how you can forget.

2. Remove the cluster from the housing by removing the 7 screws around the edge of the back of the cluster.

3. Locate the temperature compensation board below the temperature and fuel guages.

4. Push the end holders away from the board and pull the board straight out.

5. Solder a small wire from the #1 connection (farthest on the left toward the speedometer) to the #3 connection.

Put it all back together.

One word of advice, when hooking the cluster back up, beware of the red and white wire. Despite my hand drawing of the wiring, I was sure that it must hook up to something since it is nicely bundled with the rest of the wiring and begs to be hooked up to the cluster. Trusting my drawing, I first did a search and found out that this is for a tachometer and will likely damage the cluster if you hook it up to anything else.

I assume I did everything correctly since I closely followed directions from this forum and the guage seems to be working but please post a reply if I screwed something up.

I had a similar problem with my 1986 240 DL wagon. This was due to the crumbling wiring harness syndrome. The wire that goes to the coolant temperature sensor on the block goes through the grey connector on the firewall. In the 1986 model 4 wires go through this connector. The yellow wire goes to the temp sensor. Unless your harness has been updated this wire is probably in terrible condition - if the insulation has crumbled, this wire will short to any one the other three wires giving you the false overheating reading on your temp gauge. The expensive solution is to replace the engine harness with a newer harness with upgraded insulation. The cheap solution (which I did) was to bypass all 4 wires from this connector.

You are right, my 1986 240 DL Wagon does have a crumbling wire harness. Since the wiring should be the same, would you mind taking a picture of where the wires come through the firewall. This would help me a lot.

I'll try the cheap fix for now. I want to replace the whole wiring harness, but my wife is threatening to sell my Volvo if I put any more time and money into it.

tell wife wont get a cent for it if it overheats and cooks engine so best to spend $30 on an independent gauge [mechanical or electrical] so you know what is going on [incl the volvo sensor/gauge]

I just used that radiator repair "instant metal" to sort of "solder" the new bulb directly on the header of the rad [inlet side]

of course it will not help if t/stat on engine is seized shut, but engine would have blown up years ago :haha:

Looks like I fixed the problem thanks to all the advice I recieved. The yellow wire going to the temperature sending unit was falling apart and grounding against something at the slightest movement. I ran a new wire from the gray box on the firewall and it seems to have fixed the problem.

The good news is that my wagon isn't overheating. I loaned my car to a friend the day before I noticed the problem I have been afraid that she drove around overheating my engine.

The bad news is that it looks like I can continue to expect wiring gremlins to pop up until I get a new wiring harness.

these days we have flex split conduit so you can run the conduit where ever you like and replace wires as needed by simply pushing them into the conduit

have had a run right across engine for same reason as you for some years and no problems with the engine heat

At this point, you should go ahead and replace all the wires going through that gray connector. The red and black wires run under the engine to the alternator and the oil pressure warning sender respectively. Most people replace this with new wires running down the left hand side of the engine bay, threading them behind the strut tower. Use flex split conduit as the Doctor suggests. The blue/yellow wire goes to the starter. I ran a replacement wire for this in conduit with the yellow temp gauge wire. If this wire fails you will be stranded with the starter not turning over so you would be advised to replace it now. Sorry I could get a picture for you, I was on vacation last week. Regardless, I'm glad you worked it out for yourself.

Thanks for the advice. Any recommendations on where to get flex split conduit? I think I know what it is, but I'm new to wiring.

-Blake

I got mine from O' Reilly autoparts but it should be available at your local NAPA, Advance Auto Parts etc.