Coolant loss after tightening up exhaust manifold

[Big Bad Baz]

I had a very "blowy" exhaust up until fairly recently. A quick shufty revealed that the manifold stud nearest the cockpit wasn't as tight as it might be. I tightened it up, but noticed a fair amount of coolant leaking out when I did so.

 

Topped it up and thought no more of it, until I took the nose-cone off last weekend to reattach the "7" to the grille and noticed that the coolant level was rather low.

 

Why would tightening up an exhaust manifold stud cause a coolant leak and is there an optimal tightness for them to prevent this?

 

Edited by - Big Bad Baz on 10 Apr 2013 11:09:28

[Stationary M25 Traveller]

What engine ?

 

Has the stud gone in too far and pierced the waterway in the head ?

 

Edited by - Stationary M25 Traveller on 10 Apr 2013 11:17:07

[Paul Richards]

I assume you have a K series car. If so, I suspect your leak is from the water rail which is adjacent to the rear exhaust port. The flange on the water rail that connects to the head often leaks. If this is the case you will need to drain coolant, remove water rail, clean thoroughly and refit with a new gasket.

[Stationary M25 Traveller]

Sometimes you need to straighten or flatten the water rail mounting flange !

[Mankee]

This water rail leak problem seems to be rather common, as I found out recently as well. I didn't bother using a stud and nut for no. 4 primary under the water rail and replaced it with a suitable-sized cap head bolt. The head of the bolt still rubbed on the water rail ever so slightly on install, but not enough to break the seal between the flange and the head, as in your case.

 

I hate coolant leaks with passion, or any other fluid leaks for that matter, so I used two new gaskets plus a dollop of Loctite flange sealant on reassembly and it is now water-tight thankfully. In my case, after changing engines, and as SM25T points out, the front mounting bolt no longer lined up with the head, so I had to elongate the hole of the water rail and used a few washers to space it out.

[Big Bad Baz]

Yes, K Series.

 

Thinking about it, I did have to undo the bolts holding the water rail in order to get the socket anywhere near the stud. Didn't realise it had a gasket.

 

So, where on Earth would I get a new one?

[Mankee]

This is the part from Caterham:

 

http://www.caterhamparts.co.uk/product.php?id_product=2509

 

But you can use the part number to look up different suppliers and quality of gasket. I chose to go with OEM MG/Rover and got them from DVA Power, as I needed some go-faster bits at the same time.

[Big Bad Baz]

Yep, thanks, just ordered one from Caterham.

[SLR No.77]

..... and replace the stud with a cap head bolt. Caterham used to do this, the cap head bolt was even machined down to be a smaller diameter across its' head. At some stage they swapped to a stud which makes engineering-sense but fouls the water rail.

 

Stu.

[Big Bad Baz]

Quoting sforshaw: 

..... and replace the stud with a cap head bolt.

 

Again, where would I get one of them?

[SLR No.77]

I need one as well for an engine build but Caterham don't appear to list them on their site. Does anyone know the dimensions of the original bolt? It'd be fairly easy to get a few S/S bolts turned down to the correct head diameter.

 

Stu.

[Mankee]

It's just a standard M10 stud used originally. I can't remember the length off the top of my head, but I've got some standard studs in the garage that I can measure later. I've got a sneaky feeling that I used a manual cam belt tensioner bolt to replace the stud.

 

Speaking of bolts, Stu, did you get my email from the weekend? And a small package in the post?

[SLR No.77]

Hi Mankee, studs received, thanks mate I just need to get Dominic to get his finger out and send you the bolt you need 😬

 

Stu.

[oilyhands]

The bolt required is a socket headed capscrew , M10 x 25mm as Mankee suggested it is the same as the manual tensioner main capscrew, but with the head turned down to clear the water rail.

 

Make sure your two m6 bolts that hold the end of the water rail aren't so long that they bottom in the holes and that the water rail lines up correctly at the front mounting bolt after the two rear bolts are fastened, you may require a spacer at the front if it sits too far away,if you just bolt it up to close the gap it will open the rear of the flange at the back and it may leak.

 

Oily