When I got the car (1989 TPI L98) she had rusty brown coolant, so right away I flushed the coolant, swapped the upper and lower radiator hoses, and put in a new thermostat (180) and one of those blue paper gaskets with RTV, and refilled with 50/50 green coolant and distilled water. Soon after I noticed coolant pooling in the area around the thermostat housing as shown in the pictures below. It is a small leak, and doesn't seem to cause the coolant level to drop. Also, it appears to only leak when the system is pressurized. I suspected the gasket, of course, but first I replaced the throttle body heater hose because it appeared to be damaged, and I swapped it for a length of generic heater hose (something I intend to correct asap with a pre bent hose). Just today I pulled the thermostat, cleaned the housing and manifold with scraper, wire brush, and steel wool, then replaced the gasket with a Fel-pro one, the kind with the orange rubber ring, and torqued everything down. After driving about 2 miles to work, the dang thing is leaking again! The throttle body felt dry underneath, but that heater hose is a possible suspect. Could a small gouge in the thermostat housing cause a leak like this? What about a crack in the housing or the manifold? Could it be coming from the manifold gasket? I'd hate to have the pull that manifold but I'll do what I must. Any ideas/ experience would be much appreciated!

 

Almost certainly, the chinesium water outlet is warped. Most likely the bolts were over-tightened at some point in its life.

Just replace it.

New ones are mostly cast-iron. A far superior material to the one-use-only-and-throw-it-away factory garbage.

 

The bolt holes definitely showed signs of abuse, I will replace that water neck right away!

 

Don't use the RTV, I always see leaks when people put RTV on paper gaskets

You put 50/50 coolant AND distilled water?

 

Put a touch of sealant on the threads when you install the new gasket.

 

Skip the paper gasket and apply gasket thickness worth of RTV instead. We are in the 21st century now and have much better ways of keeping fluid instead of relying on a thin piece of paper.

 

My bad, I used a 50/50 mix *of* coolant and water. What kind of sealant should I use on the threads? RTV? I've ordered a new water neck and I'm going to install it tomorrow, if that doesn't work I think I will just RTV the whole dang thing. Also, what are the benefits of a 180 thermostat vs 195 degrees? I swapped for a 180 stat but I'm starting to think it wasn't necessary, given she was keeping perfectly cool before.

 

RTV doesn't work on threads. They move all the time (unless of course they're rusted solid), and the RTV inevitably gets torn up and ground into little ***** that don't seal squat. Use the Loctite/Permatex (same company... can't recall which brand name they assigned this product to) "High Temp Automotive Thread Sealer with PTFE".

There's not really any benefit to a 180° thermostat, in 2020.

 

If there is any pitting; that might be why your not getting a good seal. Use a cheap paper gasket for an even sealing surface and coat each side with high temp sealer to fill any minor voids. If the mating surface is the cause,... this should fit that. Some intakes end up pitting over time,... usually caused by an antifreeze mix that's too strong. ( measure your MIX !! )






TPI manifold thermostat housing bolt holes do not pass thru to the coolant chamber. Since the bolts do not pass thru into the coolant chamber, there is absolutely no need to put any kind of sealer on the bolt threads....... doing so will not help in any way and will only fill the whole with crap. RUN A TAP thru those holes and clean them out before re-installing anything to be sure the bolts are not 'bottoming-out' on crap that was previously pushed into the holes,... then apply sealer to the mating surface all the way AROUND the bolt holes before installing the Thermostat housing.

 

They do sometimes, particularly on some Edelbrock intakes.

 

I'll remember that,... I've never owned an Edelbrock TPI intake !

 

They don't on ANY factory intakes. Or any of the Edelbrock carb intakes I've ever worked with. Can't say about any of the 3 or 4 TPI ones that might exist out there somewhere.

But regardless, that doesn't seem to be what we're working with here. A totally moot point from beginning to end.

FOCUS on the OP's question and situation, not introduce some random rare unlikely one-of-a-kind fantasy-land ... whatever. Focus focus focus focus focus. Like a laser beam.

 

Your kidding right,...... This coming from the the guy that just recommended Loctite/Permatex instead of RTV - on the threads ??

Since ( as I pointed out ) the bolts don't pass thru to the TPI intake cooling passages; It's NOT NEEDED. Most of whatever sealer might get used there will get pushed inside to the bottom of the hole and could cause the bolt to 'bottom out' thereby not pulling the housing tight (causing a leak) or worse,... cause pressure and crack the Intake itself. ( I'm sure you musta' removed a crank bearing with grease at some point ?? ) Recommending ANY type of sealer into the intake T-Stat housing bolt holes could be considered bad advise. I didn't call you out for giving bad advise,.. I simply recommended against it - and explained why. In your haste to "throw shade' my way, maybe you missed it, So lets FOCUS on the OP's question and situation,...... shall we

Or; maybe he should just keep taking your advise,............... blindly throw $$ at (probably unnecessary) new parts and risk additional damage to already "weak" bolt holes.

 

HI ive found that sum RTV sealents should be left for 24hrs befor geting wet .may be worth a check .

 

John, you should consider a career in Presidential politics. You did as good a job of selectively editing what I said to make it say something COMPLETELY ELSE, as I've ever seen any White House press secretary or arrogant talk show host accomplish.

In reality, I recommended THREAD SEALER for the threads. Incidentally, a particular variety made by Loctite/Permatex, labelled under whichever of the brands that company uses that they assigned that product to; that being what one finds hanging on a card in the SEALER aisle at the auto parts store.

And yes, I know full well it's not needed, as I also said; but he asked what he could put on threads. So I told him about THREAD SEALER.

But I will admit, the bolts needing THREAD SEALER (or sealer of any sort) is pretty much FANTASY LAND. I'll give you that.

 

Well, the next thing I did was to replace the housing with a brand new aluminum part, then install the rubber ring type gasket dry, in addition to buying new bolts, chasing the threads in the holes with a tap, and torqueing them to 25 ft lbs. Still leaked, just as bad as before. At this point I think it must be the manifold, which does have some pitting on it although not as bad as the pictures you provided
Is it possible that the manifold has a tiny crack near the bolt holes from being over tightened, that's too small to see but just big enough to leak under pressure? I think my next step will be to use RTV on at least the manifold side of a gasket. Would it be a waste to RTV the rubber gasket? I do have an extra paper gasket on hand. In any case, I'm away from her for the next week so all work will have to wait until then.

 

At this point, might want to try some UV dye in the coolant; a trip to the car wash to clean off all that's already there; and see if you can pinpoint the source with a black light. They make kits with the dye and a little flashlight to use with it. Not much sense in further "maybe it's this, maybe it's that" games.

 

You may find incidentally, that it's one of the intake bolts... when the gasket fails, it can allow coolant to seep that way, and come up under those bolts' heads. Don't be too surprised if that's what the dye turns up.

 

Guarantee you its the throttle body coolant hose. Mine always leaks from there when I have taken the throttle body off and don't tighten the clamp enough when I put it back and it pools in exactly the same spot as in your pic. Most recently I realised the clamp wasn't tightening properly so I bought a new one and now the leak has stopped. Or maybe your gasket for the bottom of the throttle body may have perished and allowing coolant to seep out.

 

If you suspect the thermostat, then a better way to get more even and consistent clamping force is to use studs instead of bolts. It also saves the threads in the intake from getting chewed up.

I have a leak in the same area and it turned out to be the clamp for the upper radiator hose - I tightened it up and the leak went away.

 

My leading theory has been that the small amount of pitting in the manifold is just enough to seep coolant out when the system is hot and under pressure. Well, I finally cracked and broke out the RTV. I put a fine bead all around the intake manifold's mating surface, and re-used the plastic gasket with the rubber seal in it. Tightened everything down, waited for the sealant to set, and drove off. I'm happy to say, a day later and the intake is completely dry!! I think it will take a few days of vetting to be completely sure, though. In addition, I replaced both temperature sensors, and it feels good to finally have a working temperature gauge. Just one step closer to fully functional!

 

Absolutely correct. Unfortunately that wasn't the only thing leaking in my case. I had to replace the entire section of hose with a pre-bent one, since the old hose was destroyed by age. I also threw on some brand new hose clamps. I definitely don't recommend using off the shelf heater hose, like I did at first, because there's no way it can make that sharp 180 degree turn.

 

Nice ! One more "priority" checked off the to-do list; & just in time for the 21' driving season too. Time to figure out how to strap that jet engine to the hatchback !!

 

Glad you sorted it out 👍🏻