Dartht33bagger

I had a small leak around my thermostat housing when it came time to flush my coolant system, so I bought a new AC Delco thermostat housing off RockAuto and threw it on. Long story short, its leaking worse than it was before and I'm going to have to redo it. Posts on here talking about this issue were from 20+ years ago, so I'm wondering if the recommendation has changed since then. A few questions I have:

1. Can I pull the housing apart without having to drain the coolant system? I expect it to leak some but since its high up not much should drain out right?
2. I'm planning to switch back to my original housing and buy this OEM style gasket. Should I try RTV this time? https://www.summitracing.com/parts/NAL-10105135
3. Is there a better gasket I should be looking at?

Edit:

This is what I ended up doing:
1. Re-used the original housing. The new one I bought had the outlet too close to the front bolt hole which made it impossible to get a socket on it without it rubbing on the outlet neck. This is likely why I didn't get it tight enough on my first attempt because I was jammed against the housing. My original housing did not have this issue.
2. I used the FEL-PRO 35062 gasket: https://www.summitracing.com/parts/fel-35062
3. A little of the Permatex aviation form-a-seal on each side of the gasket: https://www.permatex.com/products/ga...t-liquid-4-oz/
4. Some anti-sieze on the bolts.
5. Torqued each bolt to the factory 25 ft/lbs specs in a walking succession. I started at 10 ft/lbs, then did 15, 20, and finished at 25.

vinny R

Make sure you "surface" both the housing and the manifold mounting surfaces before you install. I do not recommend using RTV. Never have never will. As long as your mounting surfaces are flat any standard gasket will work. I used a standard Fel-Pro gasket 4 years back and no leak. Also don't tighten one side down all the way, do a back and forth between the 2 bolts/nuts to seat the housing properly.

Edwardgp

You can also run a file along surfaces to file down any small imperfections

Edwardgp

Fel Pro gasket is a good choice

Dartht33bagger

What do you recommend for surfacing it? 300 grit sandpaper? Also, any ideas if I have to drain the full coolant system again?

T.L.

If the housing is not warped, and if the gasket surfaces are clean, a standard gasket with some Gasgacinch should never leak...

vinny R

Depending on how bad the surface is I think you could use 150 and it would be fine. It's ok to have some scratches present, helps it seat.
I would drain the radiator down so the level in the rad is below the T-stat housing.

kestell123

If you had a long term leak that caused rust on the intake side you may need some gasket sealer.

sofakingdom

iTrader: (1)

If the "AC Delco" one is the same chinesium crap that came stock, then that's likely to be at least part of your problem.

The better replacement ones are iron. ALTOGETHER BETTER in every way.

I would NOT recommend "OEM" gaskets either. Use the regular Fel-Pro one that's not "paper", but rather a more substantial material. Use Permatex 80019 aka #3... brown gooey glop in a can... NOT any form of silicone or RTV.

It's WWWWWWWWAAAAAAAAAYYYYYYY TOO EEEEEZZZY to get roped into stuuupid worthless crap by specifying "OEM" and "AC Delco". Pay less attention to the name printed on the box and more to the quality of the thing inside it.

Aaron R.

And when you get tired of spending all that money and time on just your thermostat housing go ahead and use a thin layer of RTV on one surface, bolt it back down, and never have a leak again.

I used to be a pefectionist. I gradually came to realize that was stupid and my time is worth too much for worry about annoying little problems like resealing a gasket over and over again.

T.L.

A warped thermostat housing will leak even with the use of silicone RTV.
I have first-hand experience with that on a F#RD.
Like I said previously; GOOD housing, CLEAN surfaces, GOOD gasket (such as that recommended by Sofa), and GASGACINCH...

Aaron R.

And when you get tired of fighting all those pesky 30-40 year old car problems just use a thin layer of RTV and move along with life.

Edwardgp

By running a file over the flat surface you will be able to tell if it is warped. The sand paper will not show warping. If you use paper put it in a sanding block.

T.L.

See my previous post. It's not always that easy...

sofakingdom

iTrader: (1)

The reason NOT to use RTV on that is, the parts MOVE too much. Too much temperature change and cycling. As the parts MOVE, the RTV TEARS and ends up, over the long term, turning into little useless LOOSE *****.

Works FINE for a year or 2; fools you into thinking it's GREAT; but eventually, it'll catch up to you.

Same reason NOT to use RTV on head bolt threads.

I don't use RTV on anything that's exposed to coolant, for this reason. It's great for many things, but not for example water pump gaskets or thermostat housings.

Intakes don't generally warp enough to cause trouble at the TH, but they DO corrode. Rather ruthlessly in fact. The file trick is equally good for dealing with that situation. Having metal that's a flat surface, no pitting and gouges, makes it MUCH eeeeezyer to get a gasket to seal.

A stock TH is made of some cheeeeeep flexible chinesium type of almost-metal. It has a "bead" on its surface, to help grip the gasket. Without that "bead" it warps too much just under the clamping force of the bolts, to have any chance of working. Filing one of those is mostly an exercise in futility: it might work for a few days or even a month or 2, but sooner or later you'll be right back where you are now. Also, since it's chinesium, it's actually a SACRIFICIAL ANODE; the natural electrolytic dissimilar-metal process will eventually EAT it, ALWAYS. Being next to aluminum makes it even worse. The only thing that's worse is a zinc one (aka "krome") around stainless steel: in fact that's why boats have "zincs" on them. The zinc ERODES in preference to the aluminum, which the presence of stainless steel causes; by the zinc eroding, the aluminum is protected.

Aaron R.

#1. The thermostat housing should not be MOVING after install. If so, something is horribly wrong. I thought this was a no brainer, but people continue to amaze me.

#2. The thermostat housing MAY expand and contract slightly with the heating and cooling of the engine. This is one of the main reasons you DO want to use RTV. RTV remains flexible its whole life. It moves with the expansion and contraction. This CANNOT be said about your standard paper/Felpro gasket. They are not particularly flexible. When surfaces are new and perfectly flat it's all good, but when they are 30+ years old and have gone through 50,000 expansions and contractions there are slight irregularities and pitting.

#3. You are correct that RTV should not be used to seal head bolt threads. The threading/unthreading will grind it into loose *****. It is for flat surfaces only.

#4. RTV works fine for DECADES without leaking. If you are experiencing a failure in only a few years it is because YOU failed to apply it correctly.

sofakingdom

iTrader: (1)

Where I come from, this is called "moving". The parts expand and contract at different rates, therefore the surfaces MOVE with respect to each other. This destroys RTV.

While RTV remains "flexible", it does not respond well to movement that tends to GRIND it. Something that retains some degree of gooey nature works better.

I've been using RTV since I worked at a place that carried it for sale to industrial users almost 50 YEARS AGO. I have a pretty damn good idea of how to "apply it correctly". I had the same idea as you for maybe 20 - 25 years, at which point intellectual humility and the willingness to objectively OBSERVE the results of my actions led me to the realization that things I had thought were perfect in the moment I did them, were far less than that over periods of decades. Perhaps after you've been around long enough to be granted the opportunity to observe the LONG TERM effects and behaviors of whatever YOU THOUGHT was A Good Idea at the time you'll come to the same realization.

Which of course is precisely why I said

in case you failed to read. Brand is largely irrelevant; the Fel-Pro ones that are NOT "paper", or Mahle or Victor-Reinz or various others, work just as well. As long as they're NOT "paper" and are sealed with something such as teh Permatex brown gooey gunk that retains its gooey attribute, rather than RTV which grinds up into little ***** due to the relative movement of the parts from expansion/contraction cycles.

Aaron R.

Well, this whole thread took a turn for the worse when couch potatoes started giving repair advice, then got so bored they decided to start a word war.

My original advice to the OP remains the same. When you get tired of fighting your leaks just use a thin layer of RTV and be done with it.

sofakingdom

iTrader: (1)

As does mine.

DO NOT use RTV on thermostat gaskets. Use something that stays gooey such as the Permatex stuff mentioned above. Will RTV "work"? Yes. Will it get you to work in the morning? Yes. Will it get you through your summer trip to the lake? Probably. Will it get your wife's or daughter's car to work 15 years from now, without you working on it some more between now and then? .... Hmmmm... whole other matter.

I'm not real fond of name-calling. Especially not by novices with short and limited real-world experience who are pretending to be "experts".

1989karr

I've used / use both. But the correct way is a gasket.


I'm not going to choose sides here but just gonna say that Ive had gaskets leak, and I've had rtv leak...especially on corroded or wonky parts.. its not a terrible pain to redo. i've had both last at least 3 years to over a decade and what not. When it leaks it may seep just a tad in which case you know its time to redo it.....IMO the thermostat should be changed every about 2-3 years followed by a good coolant flush anyway so it doesn't matter much if it leaks and what not within 3 years or so. It'll start as a very minor seepage. If it leaks before that though youre doing something wrong or your parts are fudged. ,


if you tried the gasket and it leaks again, then get some GOOD RTV and use a thin bead of that and see how it works out for ya.

NoEmissions84TA

iTrader: (1)

Just be sure to use anti-seize on the bolt threads or it may never come apart again.

alan91z28

I have a lot of thirdgens going back to ones i originally bought and changed a lot of these over the years... this is the gasket i have been using and i have never had a problem with a properly cleaned thermostat housing and intake

https://www.summitracing.com/parts/FEL-35562T

i fully agree with sofa regarding the benefit of aviation form a gasket Permatex 80019. i do not use this on the thermostat to intake surface as i have had great experience with the above FEL-PRO, but i do use this or hylomar blue on the surface of the water neck were the hose mounts combined with oetiker pinch clamp type retention

in the end good prep is a key to a lot of this

1989karr

x2 on this one!

72buickgs

I had used a cork gasket to seal the thermostat housing to the engine in my '72 Buick GS. no more leaks.

T.L.

I hate cork gaskets...

sofakingdom

iTrader: (1)

Occasionally pieces of grass, leaves, even tree bark, have fallen into motors that I had to work on outdoors. Unfortunate, but also unavoidable. They NEVER caused the slightest trouble with ANYTHING. Of course, I wasn't dumping a bag of leaves or whatever down in there; just, the odd bit would get carried in on the wind now and then, and would escape notice, or would get into a place it couldn't be gotten back out of.

I wonder... why IS that? Could it perhaps be that the internal conditions in the engine are too harsh for plant-based material to survive intact for very long? Perhaps that simple vegetable matter, much like paper, lacks the structural strength and whatnot, to deal with modern high-detergent fluids, high engine temps, etc.? Hmmmm...

What is cork, anyway??? Hmmm...

For those who don't already know, it's the inner bark of a certain species of tree. GUARANTEED to fail.

Those of you old enough to remember might recall when many gaskets were made of cork, others of some kind of paper, rear main seals were made of cotton or sisal or hemp, gasket sealer was made of shellac (a compound made by dissolving the shells of the lac insect), and so on... and motors INEVITABLY developed leeeeeks large enough and fatal enough that 100,000 miles was considered a full and satisfactory lifetime of use for one.

I don't want to go back to those days. I like engines that can retain their fluids MANY TIMES that long. Consequently I won't use cork - or rope seals, or paper, or Indian Head shellac sealer - for ANYTHING around a car.

72buickgs

I installed that gasket in 2008 & when I sold the car in 2021, there was no leak.

T.L.

That's a good thing.
I've had them leak. And they're 20th (or maybe 19th?) century technology...

1989karr

I used the cork gaskets on my 2.8.....I didn;t realize felpro made a silicone one.
The cork has held up very well for years (at least 08) and the originals were fine as well from 89 - 08. They don't leak yet... but I do recall the original cork gaskets were a PAIN to remove.


Id skip cork as much as possible just for future ease of removal.

Dartht33bagger

I pieced together all advice and redid it. After two drives I see no leaks so I think I'm good to go. Thanks all!

This is what I did:
1. Re-used the original housing. The new one I bought had the outlet too close to the front bolt hole which made it impossible to get a socket on it without it rubbing on the outlet neck. This is likely why I didn't get it tight enough on my first attempt because I was jammed against the housing. My original housing did not have this issue.
2. I used the FEL-PRO 35062 gasket: https://www.summitracing.com/parts/fel-35062
3. A little of that aviation form-a-seal on each side of the gasket.
4. Some anti-sieze on the bolts.
5. Torqued each bolt to the factory 25 ft/lbs specs in a walking succession. I started at 10 ft/lbs, then did 15, 20, and finished at 25.

NoEmissions84TA

iTrader: (1)

henryd3

iTrader: (128)

Years ago when I thought my thermostat housing was leaking a bit I took it off and resurfaced it using a file and then smoothing it nicely with 400 wet and dry paper on a verifiably flat piece of aluminum until it was very flat and nice and smooth. I picked up a Fel-Pro gasket #35562T that is thicker plastic design with rubber O ring type sealing rings on both sides. Needs no sealant or anything else extra at all and hasn't leaked a drop since. Every two years when I swap out the thermostat and fan switch to pass smog here in fun filled California I just unscrew the
two bolts and it comes right off. When switching back after passing I just make sure the housing and intake surfaces are clean before putting back together. I have reused the gasket before with no leaking, but the cheap cost of around $10 makes using a new one WAY easier than having to do it all over. Mine's a TBI so not sure if the housing gasket is the same shape as a TPI one, but it works well for me
Henry