Coolant leak from thermostat housing

[motownbrowne]

I have an 83 SR5. Today I replaced the radiator as well as the upper and lower hoses. I thought that this would be a great opportunity to replace the thermostat seeing as I already had the cooling system drained. Anyway, I unscrewed the bolts that hold the thermostat housing to the block, but only afterward did I notice the small metal pipe connecting said housing to the waterpump. I couldn't access the thermostat because of the limited mobility presented by the pipe, so I just decided to forget doing the thermostat and settle for a new radiator. Everything was good until I fired it up and noticed a leak from where the housing meets the block. I drained some coolant again and tried to spread some gasket sealer in the gap, once again limited by the metal pipe, and when I put it back together I tightened the bolts a little tighter. Fired it up, and same leak, same place, maybe a little less liquid. What do you think, my tercel has a 3A-S engine, I'm not sure if that would affect this situation, I just mention it because I didn't see any metal pipe like mine has in the 85 manual in the repair forum.

Thanks a lot, Ryan

[keith]

The thermostat sits in a shallow grove in the head. You probably knocked it out of the groove when you tried to remove the gooseneck. Remove the radiator hose from the gooseneck, unscrew the bolts, then use your fingers through the opening in the gooseneck to position the thermostat. You should be able to feel it when it falls into the groove.

[danzo]

The small pipe you are referring to may be the coolant bypass that is sealed by an o-ring as on page 193 item #7 of the Factory Shop Manual (FSM) referenced on this site. When I replaced my t-stat I discovered this o-ring that I never knew was there which had been leaking for awhile. I had a trail of coolant/rust dripping down the block near the front passenger motor mount. If you replace this make sure you use some Black RTV so the fix lasts. Good luck and let us know what happens.

[Petros]

you should be able to get the thermostate housing all apart and removed from the side of the block so you can properly clean, seal and replace the o-rings and gaskets, etc. Access is a bit of a bear, so before I'd do that I would try a $3 bottle of stop leak. Sometimes it works for this kind of thing, and it will not harm anything in the cooling system (despite the many myths from the naysayers who claim it will clog up the radiator).

Good luck.

[takza]

Might as well put a new thermostat in it...plus 2 new o-rings on the tube? Need to clean up BOTH the tube ends and the alum where they sit...using fine sandpaper...just enough to remove corrosion...not metal. Then use gasket sealer at the o-rings...best is RTV. Generic o-rings will work...just need the right diameter and thickness.

[motownbrowne]

I guess my question is just how do I get the housing separated from that bypass tube. if there is an o-ring on the side that goes into the water pump and one that goes into the thermostat housing, can I just pull it once I unbolt the t-stat housing from the block. What I experienced was just that the housing was pretty solidly attached to that bypass. What do you think?

[keith]

If you didn't twist the thermostat housing, you can follow my first suggestion. If you want to separate the pipe, it theoretically will just pull out, but its probably been in there so long that it will not pull apart easily. Corrosion builds up on the ends of the pipe inside of the o ring and acts like a c clip. Once off and cleaned up, it goes back easily.

[Petros]

it can get stuck pretty good. it is a short metal tube with an 0-ring on each end, so you simply have to work it back and forth until you work it off (strait down off the tube). Some penetrating oil might help it slip out, there can be a lot of corrosion hold it in. ONce you get it out clean the tube ends, and each of the receiving ends good, I put some grease on the o-rings so they slip in easier. If the o-rings are not damaged I have found they can be reused, otherwise replace them if there is any question.

BTW, if these o-rings get damaged and leak I have found stop leak will not seal it, same as a leaky hose, stop-leak only works on metal parts that leak.

Good luck.

[motownbrowne]

Thanks a lot guys, it is great to have such a wealth of knowledge on this forum. It was a couple of days ago that i did this project and it seems like the gasket sealer that I applied may have cured completely and solved the problem, but if it starts to leak again, I'll know what to do. Thanks again

[takza]

What you need to worry about is that IF the thermostat slipped down into the gasket area...by tightening it up , you could crack the housing. I had this happen on another vehicle...and the coolant was getting around the thermo and it would get up to temp. If it was just leaking due to cracking the gasket apart...then you might be OK.