HonestDave

Just wondering if anyone has encountered this. I put the stock intake on my 72 Olds 455 and 3/4 way through the job, the little tube of silicone that came with the metal gasket ran out. I didn't have time to go driving for more so I used some from an older tube in my tool box. Looked like similar black sealant. Later I did the thermostat gasket with it and left it sit over a week before I put my coolant back in. Couple days later I noticed the collant seeping out around the base of the thermostat housing. Looks like the old sealant is still putty-like and not hardened like silicone. I get the feeling I'm going to be re-doing the intake manifold gasket. Anyone had this sort of issue with sealant before?
Any advise?

ah64pilot

Never had that problem before but I only keep a tube a month or so after it's opened. Usually, for something like that I'll go on and get a new tube so I don't run out.

By chance did you put the rubber end seals in it? If so, it may be worth redoing it and using a bead of RTV on the end rail rather than the rubber gasket. Those always push out, whereas a thick bead of silicone will stick to the block and intake and seal much better.

HonestDave

Thanks, I'll keep that in mind about the end gaskets. There were some in from before, so I just re-did it the same. I'm beginning to wish I'd left the dual quad on it, and hunted for carbs instead. Think I'll take a real good look at the thermostat housing again and make sure it's not something stupid, like I didn't clean the neck of the housing and coolant is seeping down between the neck and the upper rad hose. I get working on so many different cars at one time, I don't always do a good job. Gets confusing at times. Glad it's not my livelyhood.

MDchanic

If RTV sealant is old enough, it will fail to fully cure, and can lead to problems like you describe.
It doesn't have to be brand new, but after a certain number of years it's kaput.

- Eric

HonestDave

I just looked at the tube I finished off with. It's called Permatex #2. Says it never hardens and it's for engine gaskets and such, but I'm not sure how the cured product behaves. Maybe it's not quite like a silicone finish. Looks like I've used two slightly different products. Could be interesting.

DeltaPace77

RTV Silicone and Permatex #2 are completely different things. The only place on a engine I use RTV, is the above mentioned front/rear ends of the intake manifold, instead of the included rubber end seals. I've been using Permatex #2 on mostly evertying else for years, with very good results. Red brush on Hi Tack sealant works well on the aluminum valley pan intake manifold gasket to cylinder head connection too.

HonestDave

I'm not sure exactly what was in the tube that came with the metal gasket. The instructions said to use it on the gasket, but the tube didn't really say what it was. Some sort of generic sealant, I suppose. I'll keep my fingers crossed, and hope the manifold doesn't leak. Don't really need too many extra adventures.

DeltaPace77

The stuff you're talking, may have been Rolls Royces Hylomar sealant, as Fel-Pro sometimes included this with their intake manifold gaskets. Good stuff.

70Post

The small tube included with the FelPro turkey tray sets is typically an RTV silicone sealant I believe. It's a small tube because the instructions only say to use it on the water ports at each end of the gasket and a small dab at the end of each head/valley rail intersection.

If you have one of the factory diecast/aluminum thermo housings it is likely warped....put a good straight edge across the underside of it and/or flat sand it a bit and you may find it's warped. Typically they are warped downwards at each mounting hole.

ah64pilot

If it is warped you might consider switching over to the RobbMC billet aluminum water neck. I have it and it is awesome!

After dyno without a thermostat, I pulled the bolts, lifted the water neck and put a thermostat in. Without doing ANYTHING else I tightened the bolts back up and it didn't leak. Great piece for the money.

HonestDave

Thanks guys, I'm going to take all of this into serious consideration. It was a Fel-Pro gasket I used, I believe. Maybe the Permatex will do the same job as the small tube of stuff and the intake will be fine. I'll check the thermostat housing for true.

64Rocket

Glue a piece of sand paper on a piece of glass or use a 4" wide belt sander. Run the thermo housing back a forth "BY HAND" and you will see how warp it is. Aluminum or the steel thermo housing, they still warp. I have double gasket it a few times. But like was said Robby Mac's housing is killer.

Gene