Minispares Stainless Thermostat Stud Kit Leaks

[svenedin]

Having suffered the well known seized thermostat housing in the past I decided to "treat" my rebuilt engine to a set of Minispares stainless steel thermostat studs, flanged nuts and washers.

https://www.minispares.com/c-str281-the ... nd-nut-kit

All was well for a few weeks. The flanged nuts looked rather smart and I smugly thought those fittings will last a very long time and it won't seize.

Then it started to leak from under the washers in two places. Naturally I assumed it just needed tightening up but it still leaked.

Reluctantly I partially drained the coolant and took off the thermostat housing. What I found was that the washers had become dish shaped and were only making metal to metal contact around a very narrow band of circumference of the washer.

Basically, the flanged nuts and washers were no good. I found some ordinary stainless steel washers and nuts and problem was immediately solved.

Looking at the underside of the flanged nut, it is a strange design that does not put pressure on the washer in the centre.

So flashy new parts often disappoint! It might actually work if the washers were thick enough not to distort.

Stephen

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[philthehill]

You are correct in that not all changes are for the better.
I have used 12 pointed self locking flanged aircraft type nuts with plain washers (to spread the load) underneath to secure the thermostat housing.
Loctite Loc & Seal should be applied to the stud threads in the head as at least one of the stud holes in the head goes through to the water jacket.
The idea of those nuts is not to use a washer, the flanged nut spreads the load and the serrations dig into the metal below and lock the nut. The use of this type of nut on alloy is dubious as the alloy is too soft. I certainly would not use them.
The holes in the thermostat housing should be drilled out to 3/8" and the studs smeared with copper ease to eliminate any seizure of the studs in the housing.

[svenedin]

Morning Phil,

Yes indeed but those flanged serrated nuts are supplied with washers in the kit. They'd wreck the soft alloy without washers. The latest thermostat housings are already drilled with the stud holes oversized so some care is needed to ensure the housing is centralised. I used Permatex thread sealant on the stud coarse threads that thread into the head and the latest Klinger type gasket.

I did try a bodge by putting some sealant under the washers but that did not work at all.

Stephen

[svenedin]

I have taken this up with the supplier. They think something has changed without their knowledge.

Stephen

[Bill_qaz]

Their response will be interesting, for that application the flange nut should be plain faced not serrated locking nuts.

[svenedin]

I had a look around online. I can't find stainless steel flanged nuts 5/16" UNF that are not serrated locking type. I did find thicker, heavy stainless steel washers 5/16" ID in table 3 and table 4 (differing OD). I will try thicker washers. It's not important now anyway because it's all dry with ordinary (stainless) nuts and washers. I like to change from an 82 C to an 88 C thermostat in Winter so it's important to me that the job is easy. The stainless fittings do also look a lot nicer than rusty ones.

Can it be that simple? A washer that is too thin and distorts. It seems that is all it is. It does show that when things go wrong it is best to stop and try to work out why. I wasted time taking the thermostat housing off, taking the studs out and re-sealing the UNC threads with thread sealant, changing the gasket and having to partially drain down the coolant. None of that was necessary!

Stephen

[Bill_qaz]

Stephen have you tried spalding fasteners
They list non serrated flange nuts
https://ebay.us/m/mvFFnJ

[svenedin]

Stephen have you tried spalding fasteners
They list non serrated flange nuts
https://ebay.us/m/mvFFnJ

Thank you. Those look good. I have used Spalding before but had looked at Westfield Fasteners this time.

I think the dishing of the washers is also related to the current thermostat housings being made with the stud holes deliberately oversized to reduce the risk of seizing. This was a common mod on the old housings that Phil mentions but it does mean that nearest the stud the washer is sitting unsupported and it seems a thicker washer is needed to prevent the washer distorting.

Basically this works like a compression fitting in plumbing. metal to metal contact making the seal. As anybody knows from plumbing, these joints are very fussy about everything being just so. Any distortion or misalignment and they leak. Over-tightening makes the situation worse and is not the answer.

Stephen

[Bill_qaz]

Westfield only seem to list serrated. I still don't think serrated is best for your application. They are more appropriate for rotational applications such as pivots were the locking is required. You are looking for maximum contact face so plain is better.
When I rebuilt mine after drilling out the broken tap found in the stud hole, I used thick flat washer and a normal nut and have had no leaks. There no need for flanged nut imho.

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[svenedin]

Westfield only seem to list serrated. I still don't think serrated is best for your application. They are more appropriate for rotational applications such as pivots were the locking is required. You are looking for maximum contact face so plain is better.
When I rebuilt mine after drilling out the broken tap found in the stud hole, I used thick flat washer and a normal nut and have had no leaks. There no need for flanged nut imho.
20250905_141012.jpg

You're absolutely right. There's no need for flanged nuts but thin flimsy washers won't do.

Stephen

[philthehill]

This is what I have used - Flanged aircraft quality locking nuts (without serrations), flat washer under the nuts, stainless steel studs with the head threads covered in Loctite 'Loc & Seal' , good quality (not cork) gaskets (just covered with a smear of grease). The stud holes through the thermostat housing have been drilled oversize to 3/8" as the Marina/Ital thermostat housing has to be turned/positioned to suit.
The spacer between the head and the thermostat housing is there to allow for the fitment of a thermostat.

[svenedin]

This is what I have used - Flanged aircraft quality locking nuts (without serrations), flat washer under the nuts, stainless steel studs with the head threads covered in Loctite 'Loc & Seal' , good quality (not cork) gaskets (just covered with a smear of grease). The stud holes through the thermostat housing have been drilled oversize to 3/8" as the Marina/Ital thermostat housing has to be turned/positioned to suit.
The spacer between the head and the thermostat housing is there to allow for the fitment of a thermostat.

Very nice. I have actually admired that engine bay in person Phil as you know!

Stephen