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fan sensor replacement...a few basic questions

Posted by thenck 
Thomas H
Vermont, USA   usa

Ok, i troubleshot my overheating problems down to my fan sensor in the radiator...failed in the off position so the fans never turn on. Got a new one...looked in my haynes manual to see what other sealant I needed, and how to go about draining just enough coolant out to replace the sensor...the damn book doesn't have ANYTHING...

1. Is there anything fancy about the sealant to use around the grommet? I Can you recommend want to use?
2. Can I just disconnect the top hose and drain the bare minimum of fluid out there...

3. Also if you can recommend what type of oil to use in the foam filter on my Weber carb that would be helpful!


Edited 1 time(s). Last edit at 04/09/2012 03:21PM by thenck.
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Thomas H
Vermont, USA   usa

disregard all but number 2....

is disconnecting the top and draining away a feasible approach to only draining the bare minimum of radiator fluid away?

Brian D
Gibraltar, Gibraltar, Gibraltar   gib

Hi...there is a retainer that holds the fan sensor in place available from moss cheap ...mgb gibdevil smiley
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BobG Avatar
Bob Gohn
North Andover, MA, USA   usa
1969 MG MGB
1977 MG MGB

Tom -
Would be helpful to know what year your car is (just add to your profile). I assume it is a 77-80 since they're the only ones with factory fan sensors (but many others have aftermarket installations that might be different).

Also, for the '77 (and I think through '79), the sensor is a simple press fit with the grommet. In '80, they changed the style to include a retainer as well, which can be used in the 77-80 cars. I do not believe any sealer is required (or desired) - just the press-fit rubber grommet. If not using the later retainer, most recommend using a zip-tie to hold the sensor into the radiator (front to back around the tank, through the fins). I may not be necessary, but it certainly makes me feel better.

As for draining the fluid - sure, just drain anough to lower the level below the sensor. You might want to search the archives (Advanced Search on upper right of the screen) for how refill and 'burp' the air out of these systems, as low antifreeze can mean the sensor is above the coolant level, and therefore not sense properly.

Norman Nalepa
Florida, USA   usa
1979 MG MGB "Chick Mobile"

I just had the same thing happen. Got the grommet from Moss. Went to Lowes got some high temp glue. Glued the grommet to the radiator. Clamped for a goos eal. Took off the clamp inserted the sensor and glied around the whole works. Working like a charm. High temp glue. Remember.
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tbarker7815 Avatar
Tom .
Knoxville, TN, USA   usa

I left the bad sensor in place, got a universal temp sensor that is adjustable, inserted probe it top right had corner of radiator, wired it up and let it do its job.
lewisrn Avatar
Bob Lewis
Danville, Indiana, USA   usa
1980 MG MGB "The "B""

On your question about draining "just enough" - I just yanked out the old sensor and jammed in the new and there was very little loss of fluid. I then topped up the system at the big bolt on the thermostat housing and it has done well since. Oh - and no sealant required for mine, even though it doesn't have the clip.

The trouble ain't that there is too many fools, but that the lightning ain't distributed right. Mark Twain
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qmg Silver Member
Ron Q
Scottsdale, AZ, USA   usa
1974 MG MGB

I have a plastic tube with a plastic bulb, like on the top of a baster. Put the tube into the top of the radiator squeeze the bulb drawing fluid into it. Remove the tube from the radiator and put it into a clean bottle, and squeeze the bulb. Just like basting a turkey. If you need to draw down a considerable amount then the bulbe can start the suction, pinch the hose and remove the bulb, place the end of the hose in a bottle. Hold the hose below the top of the radiator and you can draw down at least most of the top tank. Just remember to keep the hose end outside the radiator lower than the top tank. Hope it helps. This is a lot less messy than removing any of the hoses.
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