Thermostat Replacement Question

sptrader · 29 June 2010

I replaced the thermostat in my 92' only 2 years ago (used OEM part). I just found it "weeping" coolant from the lower right edge of the thermostat housing. Is the rubber gasket around the thermostat sufficient to prevent leaks, or do most owners coat the housing surface with sealant as well ?
(I just bought the Napa replacement and rubber gasket)

ftuhy · 29 June 2010

In Oct 2005, I used a NAPA replacment thermostat on my '96. No leakage or weeping problem with the NAPA O-ring style gasket that goes over the outer edge of the thermostat. Note that out of habit I use silicon grease on most rubber hoses, gaskets, etc and did so on that gasket.

Did you torque the housing bolts equally?

sptrader · 29 June 2010

I didn't use a torque wrench the first time, but I tried to do them equally by "feel". I plan to use a torque wrench this time(9ft lbs right ?).
It was on your suggestion(in another thread), that I bought the NAPA version this time. I'll try a little silicone grease as well.
thanks.

pgilliam1 · 29 June 2010

It's my understanding that all the rubber gaskets on this engine go on DRY. I reused the original rubber gasket when I replaced my thermostat because the parts counter person gave me the wrong one. It's holding nicely so far. But, I replaced the spool valve gaskets dry and one of them is leaking again. Maybe I should try the silicone grease

? Happy Motoring!

ftuhy · 29 June 2010

That "O-Ring" gasket has a slit in it, so that the thermostat fits into it. I don't mean to insult you, but you did slip the o-ring over the thermostat, correct? (We've all had at least one of those oh-s**t moments

)

9 ft lbs sounds right on the torque. Make sure there are not any lumps or bumps of rubber from the old gasket in the thermostat housing or the block that might be affecting the new o-ring from getting a good fit.
(And this seemed like such a simple job, didn't it?:frown

As to pgilliam1's comment on using rubber gaskets DRY, silicone grease is not a sealant that hardens or sticks to rubber, its just a lubricant. It protects rubber, keeps the rubber soft, and helps it slip into various nooks and crannies, making a better fit. That said, in most applications one needs to make sure it is only a light coating and all excess is removed. You wouldn't want it to get into the oil, for example. But, unless you left large globs of the stuff on the gasket, this is not an issue in the cooling system.

sptrader · 29 June 2010

ftuhy said:
That "O-Ring" gasket has a slit in it, so that the thermostat fits into it. I don't mean to insult you, but you did slip the o-ring over the thermostat, correct? (We've all had at least one of those oh-s**t moments )

9 ft lbs sounds right on the torque. Make sure there are not any lumps or bumps of rubber from the old gasket in the thermostat housing or the block that might be affecting the new o-ring from getting a good fit.
(And this seemed like such a simple job, didn't it?:frown

As to pgilliam1's comment on using rubber gaskets DRY, silicone grease is not a sealant that hardens or sticks to rubber, its just a lubricant. It protects rubber, keeps the rubber soft, and helps it slip into various nooks and crannies, making a better fit. That said, in most applications one needs to make sure it is only a light coating and all excess is removed. You wouldn't want it to get into the oil, for example. But, unless you left large globs of the stuff on the gasket, this is not an issue in the cooling system.

** I installed the Napa thermostat today, with a light film of "Magic Lube". I also carefully ran a razor blade over the mating surfaces and cleaned the groove that the rubber goes into. I hand tightened the bolts, then torqued them to 9ft lbs (108 inch/lbs). I bled the thermostat housing and noticed the temp still going past the 1/2 way mark, so I bled all of the bleeders once.(engine off but warm) then I noticed no hot air coming from the heating vents, with the engine running, so I bled the heater hose again(engine off but hot), after that, I had hot air. The best way I found to bleed the system, is after running the engine for 10 minutes or so, to build pressure, then shut the engine off and carefully bleed, until a steady stream of fluid comes out of each bleeder. Took a long test drive and the temp was dead steady the entire time. (and no leaks)
Thanks for all of the suggestions !
Success !

ftuhy · 30 June 2010

That's good news.:biggrin:

"I love it when a plan comes together" Hannibal, The A Team.

OLDMNSX · 30 June 2010

Just my 2 bits worth on this subject.

I use silicone grease, Dow Corning 111, on my rubber parts. It allows the o-ring to slide into position with out hanging up or rolling. Just a light coating. Never had a problem.

I ALWAYS use OEM Honda/Acura thermostats. If you look at a NAPA thermostat sitting next to a Honda thermostat you will see a noticeable difference in quality. If you don't want to have to do the job again, put in the best. They're worth the cost difference.

I have seen NAPA thermostats fail, overheat, blow the radiator hose.....it cost me having to trade off a car due to my wife loosing faith in the car. I know it's a big price for a small problem, but tell my wife that......two small children.....300 miles from home.....stranded on the side of the road.......I think you get what I am saying.

Brad

ftuhy · 30 June 2010

Brad,

I have to respectfully disagree with you on the Honda thermostat. The reason I went to NAPA is because the Honda ones are needlessly complex. The NAPA thermostat (and just about every other one in the world) uses a metal on metal closure (the disc moved by the temperature sensitive pellet and the body of the thermostat).

Honda uses a rubber O-ring on the moving disc. That O-ring can "mushroom" off of the disc and cause the thermostat to fail open. That's what happened to the factory thermostat on my NSX. I've seen that appear numerous times on Prime, and Larry B confirmed its a common failure. For that reason, I specifically went for the NAPA part - the only non-OEM part on my NSX engine/drive train.

I've never had a failure on a NAPA thermostat. In fact in the last 30 years, I've never had a thermostat failure on any car except for the NSX. Perhaps the design is a generic Honda design, and the water velocity at 8,000 rpm lifts the O-ring.

Of course, your mileage may vary. :biggrin:

Thermostat Replacement Question

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