Trying to sort out some wiring...

Heard

Heard

Well-known member
Folks...I'm trying to sort out some wiring on my 36 pertaining to the electric fan. Yeah, I know it is not supposed to have one, but it does.

The PO wired a switch under the dash to turn on the fan. The problem is that it is on all the time. It looks to be wired almost correctly in that the switch operates a relay and kicks on the fan.

But the ground side of the relay is what is not right. It has a wire that goes to two places on the right side of the engine. It goes to a sensor mounted at the top of the head about midway. Then it leaves there and goes to another sensor mounted in the water pump.

Checking this with a meter, the sensor in the head is at ground all the time which explains why the fan runs all the time. Checking the sensor at the water pump, I would expect it to go to ground at some point as the engine warms up. It never does. So....thoughts please.

My thoughts are the head mounted sensor is bad as it should not be at ground all the time. And the other one is bad also since it never changes. Am I missing something?

Also, is there any reason to have this fan controlled by 2 sensors? I guess it is a failsafe to be sure one of them actually kicks on the fan.

Thanks!!
 
Are the sensors for gauges or idiot lights ? For your application you would need one for an idiot light as it is on-off . The trick is going to be in finding one that kicks in at 180 or whatever temp you want it to come on at . Most stock ones will be at boiling or above . I would just run one in the head but others will be more familiar with this as I am used to temp gauges that are just thermometers . BTW a friend lives on the St Johns River a few miles east of 415 . I have a place by the New Smyrna Beach Speedway also .
 
I, too, don't understand the reasoning behind two sensors. This site
http://www.electricfanengineering.com/app_thermostat_sensors.html (Painless Performance sells them, too) has fan sensors that kick in/out at various temps. The problem is they have a 12 degree tolerance and that isn't good for trying to regulate an engine temp. I have one rated for 195 on/185 off and it kicks in at 206 and off at 177. I called the company and the guy told me that the sensor needs to be in the return to the water pump to work right. Doesn't make sense to me.

There are adjustable fan controllers available from about $30 on up. Do some research and find one that is calibrated to work in the range you want. Most suggest not using the type that have a probe to stick in the radiator fins. Jegs has a good selection.
 
David J said:
Are the sensors for gauges or idiot lights ? For your application you would need one for an idiot light as it is on-off . The trick is going to be in finding one that kicks in at 180 or whatever temp you want it to come on at . Most stock ones will be at boiling or above . I would just run one in the head but others will be more familiar with this as I am used to temp gauges that are just thermometers . BTW a friend lives on the St Johns River a few miles east of 415 . I have a place by the New Smyrna Beach Speedway also .
Click to expand...

I'm sure these are there just to work the fan. I also have the standard sending unit on the left head that operates the temperature gauge. This works fine. I was just curious how other folks are wiring up their fans.

I'm on the St. John's River also but I'm in DeBary, about 3 miles west of the I-4 bridge where it crosses Lake Monroe. NSB Speedway huh? ....out there by the Cabbage Patch :D
 
40cpe said:
The problem is they have a 12 degree tolerance and that isn't good for trying to regulate an engine temp. I have one rated for 195 on/185 off and it kicks in at 206 and off at 177. I called the company and the guy told me that the sensor needs to be in the return to the water pump to work right. Doesn't make sense to me.
Click to expand...

That is good to know. I've seen them at the usual places, Speedway, Jegs, Macs, etc. but I didn't think about how accurate they may be. I think I'm going to buy a couple and test them before installing them.
 
Heard said:
That is good to know. I've seen them at the usual places, Speedway, Jegs, Macs, etc. but I didn't think about how accurate they may be. I think I'm going to buy a couple and test them before installing them.
Click to expand...

I bought the one i told you about at Jegs. When the temp spread was so wide, I sent it back thinking it was bad. I bought another and it had exactly the same on/off settings. That is when i googled the part number on the sender and found the company in the link. They manufacture the units and said they are much more consistent in the bottom of the radiator or in the hose to the water pump. I considered welding a bung in a piece of exhaust tubing and placing it in the lower radiator hose but haven't done it.
 
That's interesting but I don't get it. Either the thing transitions at 185 degrees (or whatever the spec is) or it doesn't. How does 'where you place it' change that? That doesn't make any sense to me.
 
I said the same thing in my first post. I thought I might try it to see for myself before I argue with an engineer.
 
40cpe said:
I said the same thing in my first post. I thought I might try it to see for myself before I argue with an engineer.
Click to expand...

HaHaHaHa!!! So you did! Sorry. I didn't notice that. I'm going to try to wrap up my running board covers and then I'm going to tackle this project. We'll see what I come up with.
 
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