thermostat housing bolt question

[md21722]

When I changed my leaking thermostat housing gasket, I noticed the bolts for the thermostat housing were black with what I thought was oil but I'm having trouble understanding how oil would have gotten on those bolts. Do these bolts go into an oil passage on the head? Could it have been that someone oiled them??? :dunno:

 

[N8N_99xj]

might have been oiled, AFAIK they are blind.

I just had my thermostat out earlier today and my bolts were dry.

If you saw any seepage you might as well put a little dab of RTV on the threads, if the holes are blind it won't hurt anything, if there's a flaw that opens to a passage, it'll seal. (SOP for bolts that are open to coolant passage.)

 

[Thehowler]

AFAIK and SOP Really? I'm only a silly carpenter and I'm just, not as smart as you, help me out please.

 

[winterbeater]

As Far As I Know and Standard Operating Procedure. I often grease a bolt with old wheel bearing grease (black) before assembly to aid future removal in our rust belt. Wheel studs especially.

Prevents SNAFU.

 

[8Mud]

Could be someone oiled them, a trick I often use when putting old body bolts back together is to pull out the dipstick and use it to smear the threads up. I pull out the grease bucket when I've got more than a couple to do.

Could be your coolant turned acidic and turned the rust black. Coolant has kind of a slippery texture. Rust can turn black under the right chemical conditions.

I usually use a medium Loc Tite on stuff like that. Bolts or assemblies that heat and cool sometimes relax with age. The Loc Tite seems to give them a little extra grip and flexibility which reduces the chances of them loosening up. Loc Tite is also a protection, helps prevent seizing and seems impervious to coolant or oil.

I also put a light coat of silicon on both sides of the gasket for the same reason, heat-cool down cycles tend to loosen things up over the years and a little extra insurance/flexibility by coating both sides of the gasket seems to help. Some (most) gaskets do harden and shrink with age. Not really what you are supposed to do, but it works and isn't really that hard to clean off next time. I've never had a thermostat gasket leak after doing this. I'm also anal about prep, I clean things up way better than they need to be, then I do it again.

 

[md21722]

Thanks for the information!

I will speculate and say that many/all thermostat housing leaks are caused by the thermostat dropping down out of location in the head and it is not caught until he bolts are tightened. By then the thermostat housing is warped or cracked and it takes housing replacement or RTV to resolve. A flat thermostat housing does not need any RTV. Adding RTV at install time is insurance against doing it twice.

 

[8Mud]

Overdoing the silicon on the gasket can squirt some silicon into the thermostat and cause issues, I use a very thin coat. The thermostat sits in a slight recess, if it slips out of the recess while you are tightening the bolts, it may slip down and the rim of the thermostat is likely to warp the thermostat housing. I believe, but I'm not really sure, the bolts for the thermostat housing are two different lengths. I may be wrong and have it confused with another vehicle.

Some time back (years) my son was helping on the Jeep, I handed him my smeared up thermostat housing gasket and told him not to over tighten the bolts, the housing is aluminum. I figured start him out small and let him work his way up to the major jobs. Six-eight months after, I noticed one bolt was gone and the other screwed out maybe three threads. I remember thinking, I did tell him not to over tighten them but this is ridiculous and I forgot to tell him to use Loc Tite. Lessons like this I learned the hard way, usually by getting stuck someplace. But smearing up both sides of the gasket did work well, the thermostat housing still wasn't leaking.

I really don't know what happened, my son is a pain to work with, between answering his cell phone, pee breaks, snack breaks and getting side tracked I wouldn't trust my life to his automotive mechanic abilities. He usually tends to muscle brain things apart and together where finesse is called for. I really don't know if those bolts do back out of there or not, to tell you the truth, but since then I Loc Tite them in there religiously.