How to get temp sending unit out... it's STUCK!

[jayhanig]

The temperature sending unit on my 1985 GM Mercruiser 120HP I/O is apparently bad. The gauge just sits on zero even after the engine is warmed up. Grounding the sending unit pegs the temp gauge to the hot side, so the gauge itself is apparently good.

So I tried to remove the sending unit today without any success. I probably made it worse. There was a center post that the tan wire attached to that had flats behind it but putting a wrench on it just spun it within a larger fitting. The larger fitting is made of brass and I couldn't budge it, even using a cheater bar. What I did manage to do is chew it up a little. I switched from a 12 point socket to a 6 point impact socket and it slipped off also, chewing up the flats a little more. Finally I got out the lockjaw pliers and chewed it up a little more before I gave up. It's not chewed up beyond all redemption but I wanted to stop before I got it to that.

Ideas?

 

[mkast]

Re: How to get temp sending unit out... it's STUCK!

Aero Kroil

 

[Bt Doctur]

Re: How to get temp sending unit out... it's STUCK!

a small pipe wrench or remove the housing and have a shop remove it, drilling and tapping if necessary

 

[jayhanig]

Re: How to get temp sending unit out... it's STUCK!

a small pipe wrench or remove the housing and have a shop remove it, drilling and tapping if necessary

I finally got it out with a 3/4" deep dish hex socket, a socket wrench and a cheater bar. I looked at it originally with the idea of following your advice but there was no way to get the jaws of a pipe wrench in there. Really, a socket or locking pliers were going to be the only way. I hate locking pliers for what they do to metal so I gave the socket one last chance: beat it onto the fitting until it bottomed out and put some umph on it. I then had a terrible time getting the socket to let the sending unit go... I had to grip it by its threads with the locking pliers. I'm on my way to the marine supply house to see about getting a replacement. When I have it, I'll post a picture of both. The one I got out is a misshapen lump of brass now.



At least I didn't let that little bastard beat me. I have my pride.

 

[jayhanig]

Re: How to get temp sending unit out... it's STUCK!

Just a suggestion but I would run a tap into the female hole in the block to clean up the threads.

A good idea. I'll do that. Lucky for me I happen to have a tap in that size.

 

[Fishermark]

Re: How to get temp sending unit out... it's STUCK!

Also be sure when you put it back in not to use teflon tape. You can use some sealer - (I personally like Permatex) - but it needs to make electrical grounding connection to the engine.

 

[HT32BSX115]

Re: How to get temp sending unit out... it's STUCK!

Also be sure when you put it back in not to use teflon tape. You can use some sealer - (I personally like Permatex) - but it needs to make electrical grounding connection to the engine.

Me too......Some suggest NO sealant at all (Livorsi)

 

[littlebookworm]

Re: How to get temp sending unit out... it's STUCK!

I also suggest you pick up a sending unit socket. It is specifically designed to catch all the sides and corners of a sending unit. Don't use any sealant and don't overtighten. It has a tapered thread on it and will seal by itself. Hy

 

[Fishermark]

Re: How to get temp sending unit out... it's STUCK!

Ah! To seal or not to seal - that is the question!

Here's what I use - it has worked fine for me for years.

 

[jayhanig]

Re: How to get temp sending unit out... it's STUCK!

Also be sure when you put it back in not to use teflon tape. You can use some sealer - (I personally like Permatex) - but it needs to make electrical grounding connection to the engine.

The plot thickens: I put the sending unit in with a thin sealer, then ran the boat on muffs out in the driveway. Temp gauge reads cold. I happened to put my hand on the two hoses that run into and out of the thermostat housing and both of them were cold. The thermostat housing was cold as well. This is after 5-10 minutes at 1500-2000 rpm.

I regrounded the sending unit and the temp gauge pegged hot as it should. One of my buddies thinks the thermostat was removed at some point in the past. That wouldn't surprise me at all, considering the age of the boat and the fact I can only document the maintenance given in the last year.

 

[1ruralmailman]

Re: How to get temp sending unit out... it's STUCK!

or the t-stat could just be stuck wide open.good luck
rob