1986 Svo fan and coolant temp gauge not working

[ianb]

I feel like these are two separate issue's..

Does anyone have a fuse panel diagram for a 86 Svo so we can figure out which relay controls the fan?? We tested the fan and we know that thing works fine.

Also his coolant temp gauge doesnt work either..have to crawl under and make sure that wire going to the sensor near the knock sensor is still good.

Now just to reiterate the ECT on the upper intake tells the ECU to turn the fan on and the gauge is on a separate wire so those two have nothing to do with each other wiring wise?

[MAPSVO]

Just went through issues with my 85 SVO. The sensor on the top of the intake is for the ECU. The sensor on the bottom of the intake near the knock sensor is tie fan temp switch. The sensor in the block above/near the oil filter is the temp gauge sender.

The previous owner of my car reported the gauge inop eventhough he had replaced the sender. What really he did was remove the fan switch in the bottom of the intake and installed a temp sender for the gauge in that hole. The fan worked too well and turned on when the engine had barely begin to warm up. The wire to the actual gauge sender in the side of the block was off. I hooked up the gauge wire and the gauge worked. I removed the sender he installed and put the proper switch in and the fan now works properly. The fan switch and the gauge sender are the same thread and will interchange. This applies to my 85. I have a 86 also and believe but am not sure it is the same configuration.

[Jimmy2.3Mustang]

Now just to reiterate the ECT on the upper intake tells the ECU to turn the fan on and the gauge is on a separate wire so those two have nothing to do with each other wiring wise?

Um, yes and no.

The fan system is completely independent of the ECU.

The gauge is also completely independent of the ECU.

So yes they have nothing to do with each other, and no they have nothing to do with the ECU.

The fix for the gauge is probably going to be the switch, wiring, or a problem with the gauge. The problem with the fan is probably the controller/relay module under the dash, or you're not waiting until the engine hits 230* when the fan switch turns on the fan. MAPSVO is dead on with the sending unit descriptions/locations. The ECU only interacts with the one sensor and it's only used to control the engine. The temp gauge runs solely off the sender, and again doesn't have a thing to do with the fan. The fan is controlled only by it's switch and relay. The fan relay is a small black box, probably says TRW on it, you'll find it next to the steering column below the fuse box. It's a really safe bet that when you unplug the harness from the relay the terminals will be melted into the plug. The fix is either to replace the box and the pigtail on the harness, in which case it'll probably just melt again, or replace the stock relay with something more appropriate. Do a search and you'll find that topic has been covered in great detail already.

[ianb]

Um, yes and no.

The fan system is completely independent of the ECU.

The gauge is also completely independent of the ECU.

So yes they have nothing to do with each other, and no they have nothing to do with the ECU.

The fix for the gauge is probably going to be the switch, wiring, or a problem with the gauge. The problem with the fan is probably the controller/relay module under the dash, or you're not waiting until the engine hits 230* when the fan switch turns on the fan. MAPSVO is dead on with the sending unit descriptions/locations. The ECU only interacts with the one sensor and it's only used to control the engine. The temp gauge runs solely off the sender, and again doesn't have a thing to do with the fan. The fan is controlled only by it's switch and relay. The fan relay is a small black box, probably says TRW on it, you'll find it next to the steering column below the fuse box. It's a really safe bet that when you unplug the harness from the relay the terminals will be melted into the plug. The fix is either to replace the box and the pigtail on the harness, in which case it'll probably just melt again, or replace the stock relay with something more appropriate. Do a search and you'll find that topic has been covered in great detail already.

Thank you for this..we will inspect that TRW box and see whats up..so if its not melted we could try slapping in a new relay first. I thought the ECT on the upper intake controlled the fan by going threw the EEC first. I didnt realize it was a much simpler setup. Im also going from a turbo coupe so obviously our cars are different. Ill try to search more about this melting box and see what a good permanent fix for it might be.

Thanks again

[ianb]

Also for a quick fix where would you guys recommend getting the relays? I saw some on Rock Auto but I wasn't sure of the quality of the parts..any advice on which one we should order if the relay and or switch is shot?



Thanks for the help

[Jimmy2.3Mustang]

87-88 Turbocoupes use a ECU controlled fan relay, but everything else (including earlier Turbocoupes) use the separate switch and relay system.

Make sure that the engine is getting really hot before you decide the fan system isn't working. Stock turn on temp is something like 220* +/- 5*, so 230* isn't too far fetched. On the stock gauge that's well past the middle of "NORMAL". With the stock setup mine would only come on in bumper to bumper summer traffic, or sitting in the drive thru when it's 101* outside.

Trouble with the stock system, is that it comes on so late it can't really catch up and cool the engine back down. At best, it'll hold the temp until traffic starts to move and you get some air through the radiator. That's when every part of it works perfectly. The fan itself is durable, but the relay is really a mess. Ford used a card edge connector on the relay board, which really isn't up to carrying the amps the fan draws. Remember the old video game systems, when you'd power on the system and get garbage on the screen, pull out the cartridge, blow it out, and try again? Now imagine that instead of garbage on the screen you just get heat from a faulty connection. That's the problem with that type connector. Even if everything is in perfect condition it's still hokey. Fortunately when it fails, the fan will probably just stop working letting the engine overheat, rather than burn the car to the ground.

What I did on my car was wire in an aftermarket heavy duty relay (if I had A/C it'd take two relays to function like stock), with a manual override switch so I can trigger the fan relay when I know I'm going to be idling awhile. I also switched to a slimmer profile fan to make room under the hood. I'm still using the stock fan switch that seldom comes on, but plan to either replace it with one having a lower on/off temp, or use the LA3 fan control to trigger the relay.

[Jimmy2.3Mustang]

Here's the stock wiring diagram... You can see how the relay module is just two relays on a printed circuit board. It'd be easy enough to test if they're working.



I wouldn't bother replacing the relay, even if it's bad, a new one would still be barely adequate. Besides that, it'll be the wiring harness plug that snaps into the relay that will be melted. I used a Delco GM 30 amp heavy duty relay for an early 90's GM car.