Inlet manifold gasket – polyurethane or silicone sealer?

[Capperdog]

Hi all, I’ll be changing inlet manifold gaskets tomorrow and planned to use a small smear of polyurethane sealant on the gaskets – probably Tiger Seal, but I have others. Before doing this I thought I would just check the latest wisdom within the forum, which I think on the whole supports the p.u. option as opposed to silicone. Great, that’s what I felt was best too…

Until I checked the temperature range of several p.u. sealant products. They all appear to say operating temperatures up to 90degC is fine, with short periods at 120degC ok too. Now, I know our thermostats are usually rated at 82deg (some 78 and some 88 out there too) but that’s water temp and I expect the heads themselves to run a little hotter than the water/coolant taking the heat away.

So my question:- is it better to use a silicon gasket sealant which is usually rated as stable at 300+degC (some 600degC!) or use the polyurethane gasket sealant which has lower temperature limits but much better grip and gap filling qualities?

Knowledge and experiences greatly appreciated

[richardthestag]

to be honest, if everything is lined up and the gasket is correct thickness then stag wellseal does the job well enough.

Alas this is not always the case, heads are skimmed without thought for the inlet manifold etc. if it is close but not perfect then tigerseal.

Pity the next chap down the line who has to remove the remains from the heads and inlet though

[Goldstar]

I generally use an rtv and haven’t had an issue yet.

[NeilR]

Silicone (RTV & the like) is for bathrooms & double glazing - not cars !!!!.
PU everytime, it's just a swine to get it apart again if you have to.

[richardthestag]

Silicone (RTV & the like) is for bathrooms & double glazing - not cars !!!!.

Buy an automotive, oil resistant RTV and you will have no issues. PU is great for gluing panels together and is a weapons grade PITA on engine parts.

I am never a fan of using a zip wheel on an angle grinder to remove the gasket remains, it is a bit like cretins who dip an entire thread in thread lock before fitting. I have invented many swear words for folk who do this

[mole42]

Mine were siliconed when I bought the car, failed pretty soon. Latterly, for the past 30,000 miles, I’ve used Wellseal. Just changed a set of gaskets today, the ones from Rimmers failed leaking from the long slot into the V, the new ‘improved’ ones from Wards might be better. Make sure to check the flatness of the manifold faces and check the fit against the head with a feeler gauge. Check the thread in the bolt holes !

[richardthestag]

Agreed Richard, So many folk do not pay enough attention to checking that the inlet manifold and head faces are parallel.

Then they over tighten the bolts and pull the threads and somehow that is an engine design issue

[Goldstar]

Buy an automotive, oil resistant RTV and you will have no issues. PU is great for gluing panels together and is a weapons grade PITA on engine parts.

I am never a fan of using a zip wheel on an angle grinder to remove the gasket remains, it is a bit like cretins who dip an entire thread in thread lock before fitting. I have invented many swear words for folk who do this

Absolutely correct. NeilR im afraid you’re talking out of your inlet manifold

[Capperdog]

Oh I dream of matching heads and manifold... I'm doing the gasket change because the manifold had to come off a week ago to fix a couple of other problems with it so I put a different manifold back on for speed of temporary repair - I have a few of them hanging around :-)

Anyway, I have now finished the repairs to the “original” manifold and will be refitting it tomorrow with new gaskets of the “improved design” type. It should be a good fit as it is the one I used when bolting the heads and manifold down together 6 years ago. I will be checking the bolt holes, bolt lengths, cleanliness and alinements, plus a dry run of nipping up the bolts and feeler-gauging around.

And following on from all the good advice/feedback from all of you, I will be using a sparing amount of Tiger Seal (polyurethane) on the gaskets whilst hoping not to have to clean it off anytime in the near future. Having run the car for the past 40 years and now on the fourth time round the clock you can guess there aren’t many jobs I haven’t had to do – a true Trigger’s broom of a car! But cleaning and prepping gasket joins has always been one of my favourite ones… not!

[marshman]

I am with NeilR. PU (Tiger Seal) everytime on the inlet manifold gaskets. Not that hard to get off with a sharp chisel or Stanley knife blade, don't think anyone said clean it off with an angle grinder. I hate RTV or any silicone based sealant, automotive or not, it is a real pain to clean off as it is so spongy. Also seems to "squish"" out more. Have dismantled numerous old engines and found clumps of it blocking oil pickups etc where there has been over zealous use by "ham fisted gibbons"

I know of one much reverered so called Stag specialist not far from me that uses Silcone sealant for core plugs as well as just about mating surface on the engine, took me ages to clean it all out and do the job properly when I rebuilt my engine a year or so back after it the previous owner had it rebuilt, at great expense I might add, by them. I was horrified when I saw the excess which ended up where it shouldn't.

The Stag engine, along with the majority of engines of that era were designed with mating faces that needed a decent gasket and a smear of Hermatite or Wellsreal. The manifold is an issue if heads have been skimmed or the manifold has been over tightened distorting the flanges and the fit is no longer good, probably aplied to most engines by now. That is where PU type sealants come in and do a good job that lasts.

[sxl01]

Hi all, on the subject of the inlet manifold should/or not necessary to coat the steel bolts going into the aluminum head to prevent corrosion and seizing, if so would loctite be suitable? The bolts on my head appear to be coated in something and were a little tight to remove, ta

[jbuckl]

If you are thinking of an anti seize, use sas aluminium anti seize… copaslip encourages galvanic corrosion.

However, snugging the manifolds to heads during rebuilding is often overlooked and a root cause of manifold sealing issues.
Heads must only be torqued after manifold fit has been established.

Therein lies a massive oversight in many stag engine rebuilds.

pu sealer is your friend if that happened.

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[sxl01]

Thanks for that jbuckl

[jbuckl]

Elring dirko or victor reinz ‘rtv’ sealants seem to also be suitable for manifold sealing issues, but p.u. Tiger seal or m.h.p. Are ‘proper’ gap fillers to get you out of the previous bad practice.