Garage > Mechanicals

Thermostat housing problems - corrosion, pitting and shot threads

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Jan S:
Engine is 1977 US M100.985 (6.9), from a 450 SEL

I've started the job replacing the thermostat and a few cooling system hoses.

Not surprisingly, I was met by a few challenges:

Problem #1: the threads for one of the four bolts connecting the thermostat housing cover is shot (upper left thread hole), and a previous owner has solved (?) the problem by filling the threads with silicon and using a screw instead of a bolt. My goodness!

My plan is to talk to a professional workshop and see if they can fix it by inserting new threads for a smaller bolt. I guess I have one try to fix this properly. Any other suggestions?


Problem #2: the lip on the cover is severely corroded/pitted. I'm not sure to which degree this will cause a leak.

My plan is to use the thicker of the two rubber seal rings (the thermostat came with two rubber seal rings, one slightly thicker than the other). The lip on the cover plate will push the seal down and out - i.e. seal against the thermostat and the outer wall of the housing. In addition I plan to use a thin layer of sealer/silicon on the outer surface between cover and housing. I will clean all the relevant surfaces and may try some JB Weld where the pitting is unacceptable. Any suggestions/ comments?


Problem #3: the water return pipe - connected to the water pump with a hose - is severely corroded (see pic).

My plan is to clean and sand as much as possible, before I put on the new hose. How about sealing the corrosion with some Miracle Paint? Will that stop the corrosion getting worse? Any other suggestions?

(https://www.ebay.co.uk/itm/Bill-Hirsch-Miracle-Chassis-Underside-Rust-Killer-Specialist-Coating-Paint-Black-/323364698182?var=0&mkevt=1&mkcid=1&mkrid=710-53481-19255-0&campid=5338268676&toolid=10044&customid=Cj0KCQiAhMOMBhDhARIsAPVml-GfbhkR7Twxy9xQ3j-P-5ff95KZauP-opbVpSogiPnlQmREEcWw8isaAi3oEALw_wcB? 


In general - I've read some acids can remove corrosion. Any product tips and/or specs?

ptashek:
#1 you could drill out the hole, and have a thread repair coil inserted. That's a permanent fix if done right. One issue might be finding those in aluminium.

#2 maybe time to get a replacement? Or if you know someone who can weld aluminium that'd be another route - weld the pits, and file them down flush.

Alec300SD:
Regarding problem #3, see my attached post for my workaround  for the damaged iron heater pipes.

http://www.peachparts.com/shopforum/4037206-post1.html

PosedgeClk:

--- Quote from: ptashek on 14 November 2021, 08:29 AM ---#1 you could drill out the hole, and have a thread repair coil inserted. That's a permanent fix if done right. One issue might be finding those in aluminium.

--- End quote ---
A helicoil is a good route, and there is not any good reason to need aluminum on aluminum. You aren't passing current through this junction. A steel helicoil will work beautifully in an aluminum body.

If you wanted to spend money and make a DIY job out of it, you could use McMaster's site for reference. I would call around though and just find someone with the tooling already.

https://www.mcmaster.com/helicoils/helical-inserts-with-installation-tools-7/

Jan S:

--- Quote from: ptashek on 14 November 2021, 08:29 AM ---#1 you could drill out the hole, and have a thread repair coil inserted. That's a permanent fix if done right. One issue might be finding those in aluminium.

#2 maybe time to get a replacement? Or if you know someone who can weld aluminium that'd be another route - weld the pits, and file them down flush.

--- End quote ---

#1 Yes, thread repair coil might be the way to go. I need to remove the silicon to assess the thread damage.

#2 My first thought was JB Weld, but alu welding is a good idea! I will check with a local firm that welded my rims a few years back.

Thanks!

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