How to remove broken thermostat cover from powerhead?

[six50joe]

Cooling system work over the weekend on my 1998 Johnson 150hp OceanRunner. I put in a new water pump, then went on to what should have been the easy part- or so I thought.

I went to put in a new pair of thermostats. I thought the threaded plastic covers would come out real easy with an adjustable wrench or channel locks. I was wrong. I thought there should have been an O-ring behind the cover heads, but It appears that a previous owner had put some kind of sealant on them instead. That sucker wouldn't budge, and I ended up breaking up the hex head while trying to undo it, to the point that nothing could get a grip on it anymore.

I later on found out that I would probably have had better luck heating it up with a blow dryer for a few minutes before trying to loosen it, but beyond that point now. There's only one option, to clear out what remains of the broken cover, which is mostly just the threaded part at this point. The thing is, I'm not sure how to go about doing this in a way that I don't risk damaging the threads in the powerhead. Looking for advice from the smart folks out there.

Picture shows what it's currently like.

 

[Roberthill]

Re: How to remove broken thermostat cover from powerhead?

You can try to dissolve the plastic by using acetone , fingernail polish remover or M.E.K ,its going to depend what kind of plastic it is .

 

[six50joe]

Re: How to remove broken thermostat cover from powerhead?

You can try to dissolve the plastic by using acetone , fingernail polish remover or M.E.K ,its going to depend what kind of plastic it is .

Not sure how I'd find that out. This is the cover:
Amazon.com: THERMOSTAT COVER | GLM Part Number: 13730; OMC Part Number: 332944: Automotive

Is it safe to try any of the dissolvents you mentioned if I don't know?

 

[Roberthill]

Re: How to remove broken thermostat cover from powerhead?

Stat cover screws into head which is aluminum , non of the solvents will have any effect on the head . Don,t spray or douse but put some on a rag and let it set on the cover then see if it soften up any .

 

[kodibass]

Re: How to remove broken thermostat cover from powerhead?

Take a flat screw driver heat the last inch of the tip with a propane torch until red hot, melt a notch or 3, then gently pry out the remains.

 

[philroth]

Re: How to remove broken thermostat cover from powerhead?

There's only one option, to clear out what remains of the broken cover, which is mostly just the threaded part at this point. The thing is, I'm not sure how to go about doing this in a way that I don't risk damaging the threads in the powerhead. Looking for advice from the smart folks out there.

Picture shows what it's currently like.

I have the same exact issue on a Johnson 50 hp (1994). Can you tell me what you ended up doing to remove the plastic threads. And did you end up removing the Cylinder Head the Thermostat Cover screws in to to remove the plastic threads?

 

[six50joe]

Re: How to remove broken thermostat cover from powerhead?

I have the same exact issue on a Johnson 50 hp (1994). Can you tell me what you ended up doing to remove the plastic threads. And did you end up removing the Cylinder Head the Thermostat Cover screws in to to remove the plastic threads?

I haven't yet been at my boat's location since I made the post, so I haven't tried anything yet. I'll be there in a couple of weekends and will take a shot then. I'm going to try the dissolvent on a rag method first. If that doesn't work I'm going to try the torch-notching method. It seems that if there was a tool with a small, tight hook at the end I'd be able to break it up by grabbing it from the inside and pry it enough to break it inward. Haven't seen anything like that but am keeping my eyes open.

If you get to your problem before I do mine, would be great to hear your results.:thumb:

 

[philroth]

Re: How to remove broken thermostat cover from powerhead?

Here is what I did to remove my Thermostat Cap
Removing Sheared Off Thermostat Cap (Plug) - YouTube

 

[six50joe]

Re: How to remove broken thermostat cover from powerhead?

Thanks for posting that! I'll have my chance to get to that this weekend. Did the method shown in the video work for you well? Was it easy to get the sheared cap to turn?

Here is what I did to remove my Thermostat Cap
Removing Sheared Off Thermostat Cap (Plug) - YouTube

 

[RogersJetboat454]

Re: How to remove broken thermostat cover from powerhead?

Take a flat screw driver heat the last inch of the tip with a propane torch until red hot, melt a notch or 3, then gently pry out the remains.

When all else fails, this ^^^^ should work.

I've run into this sort of situation with GM trucks before. They had some stupid adapter that threads into the intake manifold for one of the heater hoses to clip into. The adapter starts leaking, and is made out of pot metal, so 9 times out of 10 when you go to replace it, the threads snap off flush in the intake manifold. It is about the same inside diameter as the cap you are dealing with now.

The solution to getting those out is similar to what Kodi posted. Notch the inside of the adapter to just shy of the threads (weakening it). I usually did 4 notches carefully with a hack saw blade. Then you place a flat screw driver on the very edge, and pry away the quarters from the threads.

Since this is plastic (and plastic melts), you should be able to do what Kodi suggests with out damaging the threads on the head.

 

[six50joe]

Re: How to remove broken thermostat cover from powerhead?

Ok, mission accomplished, though it was still a pain in the butt.

Of the above methods, the one that was effective for me was the torch-screwdriver notching. I had been hoping the method in the youtube video would work, but there wasn't enough meat for me to grab onto with a needlenose. It took a lot of heating up and burning deeper notches to get it to the point where I could just about pry up a chunk with a pick. Took a lot to get to that point, but went easy after that.

Now, looks like I gotta go out and spend over $100 on a wrench with a 3/4" drive and a 1 1/2" socket to get the new cover in. Not going to risk shearing again with an adjustable wrench or channel locks.

 

[RogersJetboat454]

Re: How to remove broken thermostat cover from powerhead?

Now, looks like I gotta go out and spend over $100 on a wrench with a 3/4" drive and a 1 1/2" socket to get the new cover in. Not going to risk shearing again with an adjustable wrench or channel locks.

No need to spend so much;
Craftsman 1-1/2 in. Socket, 12 pt. - Tools - Ratchets & Sockets - Sockets & Socket Sets

Or if you want a 6 point socket..
Craftsman 1-1/2 in. Easy-To-Read Impact Socket, 6 pt. Standard 3/4 in. Drive - Tools - Air Compressors & Air Tools - Impact Sockets

+

Craftsman 1/2 to 3/4 in. Socket Adapter - Tools - Ratchets & Sockets - Socket Accessories

 

[six50joe]

Re: How to remove broken thermostat cover from powerhead?

No need to spend so much;

Funny, I guess that's what I get when I send my wife to buy hardware for me :facepalm:

She came home from Sears with the first socket you mentioned, and told me the salesperson said my only option is to buy one of their 3/4" drive wrenches to use it. I was hoping someone would correct me on that, thanks :happy:

I didn't know they had a 1/2" - 3/4" adapter but that should do the trick.

Thanks for your followup.

The SELOC book says to tighten the cover to 110lb ft lbs if I remember (if not very close to that). Seems like an awful lot of force given how easy it was to break while trying to remove it.

I only have a 70lb torque wrench. Am I asking trouble if I limit it to that?

 

[RogersJetboat454]

Re: How to remove broken thermostat cover from powerhead?

Funny, I guess that's what I get when I send my wife to buy hardware for me :facepalm:

She came home from Sears with the first socket you mentioned, and told me the salesperson said my only option is to buy one of their 3/4" drive wrenches to use it. I was hoping someone would correct me on that, thanks :happy:

I didn't know they had a 1/2" - 3/4" adapter but that should do the trick.

Thanks for your followup.

The SELOC book says to tighten the cover to 110lb ft lbs if I remember (if not very close to that). Seems like an awful lot of force given how easy it was to break while trying to remove it.

I only have a 70lb torque wrench. Am I asking trouble if I limit it to that?

IMHO you're asking for trouble using a Seloc manual (they are often WRONG when it comes to spec's and procedures).

Are you sure its 110 foot pounds, and not 110 INCH pounds?

I can't imagine ANY piece of plastic ever being torqued to 110 ft.lbs.
110 In.lbs would be roughly 9 ft.lbs converted, which would make allot more sense.

 

[six50joe]

Re: How to remove broken thermostat cover from powerhead?

110 In.lbs would be roughly 9 ft.lbs converted, which would make allot more sense.

Don't have the manual with me this week, but you're probably right, I must have misread it. I don't have the service manual for my outboard, so for me it's either Seloc or guessing.

Sealant was used when the covers were put on previously, but my local marina had said it isn't necessary for thermostat covers. He in fact said he uses a little marine grease on the cover threads which actually helps give it more of a seal. Any opinions on that?

 

[RogersJetboat454]

Re: How to remove broken thermostat cover from powerhead?

Sealant was used when the covers were put on previously, but my local marina had said it isn't necessary for thermostat covers. He in fact said he uses a little marine grease on the cover threads which actually helps give it more of a seal. Any opinions on that?

Could see what the OMC experts here have to say.

If the dealer is having good luck with it, might be worth a shot. Worst cast is it dribbles a bit, and you take it apart and re-seal it.

 

[six50joe]

Re: How to remove broken thermostat cover from powerhead?

Could see what the OMC experts here have to say.

If the dealer is having good luck with it, might be worth a shot. Worst cast is it dribbles a bit, and you take it apart and re-seal it.

Exactly my thought. It will only be used in fresh water, so not a catastrophe if there's a minor leak.