I was trying to get my 86 to turn the fan on at a lower temp. I ordered a new sensor that was to work on at 200 off at 185. it was the sensor between the 6 and 8 plugs. I stared to change it and found that it had different threads so I looked at the one on the front of the intake it had 2 wires and the end of the plug was desentigrated. I got it pluged back on like i thought it should be. then I got a bushing and installed the one I had purchased in the head. When I started the car the fan ran constantly I found the problem was the desentigrated plug had the prongs touching each other. I purchased a new coolant temp sensor with new plug installed it. Now fan wont come on temp readout never comes off of low temp. Is there a fuse or something or should I just put all of my old stuff back on. All I have is a Haynes book and the wiring diagram shows old school dash hard to decifer. Any help would be greatly appreciated.

 

There are two or three temperature sensors (if you have the auxiliary fan).

The temperature sensor in the passenger side head between plugs #6 and #8 is the sender for the temperature display in the instrument cluster.

The one on the front of the intake manifold goes to the ECM. The ECM determines when to turn on the main fan. The only way to change the temperature is to reprogram the EPROM.

If you have an auxiliary fan in front of the radiator, it is controlled by a temperature switch in the driver's side head between plugs #1 and #3. You can change the auxiliary fan turn on temperature by buying the appropriate temperature switch.

 

I am worse off than I thought. I bought a switch that was supposed to turn the fan on at 200. I was completely backwards on the switches. how do I get the fan to come on at 200 I've already had 2 heads cracked because it got to hot I just want it to run cooler don't like to be that close to boiling. Can I reprogram or do I need to put a manual switch or aux. fan????

 

Something sounds screwy. If it was me I'd flush the block and make sure fluid is actually getting through. If water is not getting to the temp sensor it will not read correctly. While I was at it I would pull the radiator and have it checked at a radiator shop. I am sure by now you have already changed the T-stat, but thought I'd mention it as well. Of course it could just be you got a bad part or hooked it up wrong, but w/ 2 cracked heads I would not trust any part of the system til I was sure.

Usually what I do is remove the T-stat and bolt the neck back on, then remove the hoses at the radiator and run water through the block from the top and make sure it runs freely out the bottom. You can do the same for the radiator but the results can be inconclusive as it may have a few rows that work and most that don't, so I usually take it to a professional to check it.

Anyway I am not familiar with that block so I could not say for sure if this is the right way to go about it, but FWIW there is my 2 cents.

 

Put the switch in DS head and splice it's wire into the dark green/white stripe wire at fan relay. Fan relay is on inner fender in front of battery.

If you have the booster fan in front of rad, you will already have a switch in DS head. You could just replace it with the lower temp switch and if you like, you could still splice into the main fan relay and have both come on early.

http://members.shaw.ca/corvette86/Co...%20Control.pdf

 

I would check radiator and cap for holding pressure. Clean out between radiator and AC coil, Check water pump is actually pumping water, lower radiator hose is not collapsing and blocking flow to pump, flush cooling system and install real 50/50 mixed coolant, 200 degree switch with 192 degree thermostat with a 1/8 bleed hole in it. There are just so many things that make it run hot and most are age related. Just adding a switch is a band-aid on a bleeding artery..

 

I just rebuilt the engine and every thing is clean but before I rebuilt it it had gotten hot quite a few times before rebuild the fan came on at 235 went off at 216 it ran great but in the summer it would loose water and running that hot you didnt know you were low until it was to late. Since the rb the fan comes on at 216 turns off at 200(not sure why this changed) I am not comfortable with this in traffic like this summer it was 114 out side and I was going above boiling and was loosing water again. When your in traffic and shes low on water you don't know it till it passes 216 time you get were you can pull over some where to do something you are way passed that then cool down to were you can add water you have been on the side of the road for a while and you dont know what you have done to the motor. This was the cause of the heads breaking from what the machinist said he showed me the thin spot between the exhaust ports in the center one was visable the other showed after cleaning. Cooling system works great fan comes on cools down shuts off heats right back up we just toggle 200 216 back and forth. I dont like seeing it 216 I dont care about alittle lost performance I like the idea of cutting this new switch into the fan relay then putting the old one back in the 6 and 8. Thank ya'll for your help she doesnt need to be a winter car she doesnt like rain, I know she won't like ice. LOL

 

It seems like your still saying you are still loosing coolant/water after the rebuild you did for whatever reason... Is this correct?

If your still loosings water/coolant mix chances are very good that you've got, getting or will get steam pockets within the coolant system. Steam pockets can kill a set of aluminum heads, heater core and more in a very small amount of time. If your still loosing/boiling off coolant find the problem and fix it ASAP....like it or not a L98 running at ~245 degrees with the proper coolant mix will not boil off and should be just fine.