Name this sensor?

tom82cj8

Scrambler Pro
City
Austin
State
TX
#1
This is a sensor in my intake manifold. I believe it is in the coolant, but it is not the temp gauge sensor. What is it for? I would like to replace it with a temp sensor for my new electric fan setup.




Thanks,
 

John N

Addicted....Ex-SOA VP
LIFETIME
CJ-8.com Member
SOA Member
City
Rockville
State
VA
#2
I think I'll call it Fred......

I'd agree, Fred looks like a coolant sensor. :D
 

tom82cj8

Scrambler Pro
City
Austin
State
TX
#3
What is it for?

I cannot think of anything that is controlled by that sensor especially since I am using the GM TBI. I was thinking that it might have controlled the electric choke or something along those lines. At any rate, I thought I would ask before I toss it in the parts drawer.....

-Thanks,
 

okjeep

Basic User
City
Tulsa
State
OK
#4
I think that sensor was part of the electronic (crappy) carb system that jeep tried. If you follow the wire, it would go to the old computer that was under the dash.
 

jscherb

CJ-8 Member
CJ-8.com Member
City
Elmira
State
NY
#5
That's the temp switch for the intake manifold heater. Below 160 degrees the switch inside is closed; it grounds the circuit to power the manifold heater relay (relay is on the firewall roughly above the back of the intake manifold); this relay in turn supplies power to the heater plate which is on the bottom of the manifold under the carb (or throttle body, in the case of GM TBI).

I recommend you keep it in place. The manifold heater helps keep the fuel atomized on cold start. This applies equally to carbureted or TBI setups.

BTW, also in that circuit is the oil pressure switch on the other side of the engine. The manifold heater is a fairly high current device so it only is powered when a) the coolant temp is below 160 degrees AND b) there is oil pressure (i. e. the engine is running, therefore the heater runs off the alternator and not the battery).

Jeff
 

tom82cj8

Scrambler Pro
City
Austin
State
TX
#6
I thought that it my be related to the manifold heater. I am going to do some diagnostics and see if it is currently operational.

Any suggestions on where to install a 3/8 NPT coolant sensor???? I rather not use a tee.

Thanks,
 

jscherb

CJ-8 Member
CJ-8.com Member
City
Elmira
State
NY
#7
Here's what you need to do to test (from an article I did for jRations issue 8):

"There are two simple tests to ensure the manifold heater is working properly. These tests must be performed when the engine is cold:

1. Pull the plug from the oil pressure switch and put a jumper across the two contacts in the plug. The jumper is to simulate oil pressure. Turn the ignition switch to the on position and put your hand on the bottom of the intake manifold under the carburetor. You’ll feel a round plate about 5 inches in diameter. Within a minute or two, this plate should get warm. If it does not, either the heater is bad or the temperature switch is bad. You can jumper the temperature switch and try again to eliminate that as a possible
cause. The temperature is switch towards the rear of the intake manifold, near the #6 cylinder.

2. After performing the first test and verifying that the heater does in fact warm up, reconnect the plug to the oil pressure switch. Unplug the connector feeding power to the heater and connect a voltmeter to the connector on the vehicle harness side. Turn the ignition switch to the on position. You should register no voltage at the connector. Start the engine and you should see voltage at the connector, this verifies that the oil pressure switch is operating properly. If you keep the voltmeter connected until the engine warms up, you should see the voltage switch off at about 160 degrees.
 
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