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Old 11th March 2018, 17:56   #1
Randyjim
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Default KV6 O-rings AGAIN!

Good evening readers!

I've been out this afternoon to do the routine maintenance checks, and had to top up the coolant a little. The o-ring at the bottom of the banana pipe is the source of the leak and not for the first time.

I thought I was doing well with the viton O-ring and molykote 111 combo, they seem to have lasted about 9 months this time, but no such luck.

When I first changed the thermostat (failed open, but not leaking), I found a significant scored mark on the side of the bore on the block which I rubbed back as best as I could, but I'm worried it's left enough damage to be causing repeat failures.

Can anybody offer any advice on repairing the bore, or should I just fill it with silicone sealant if I can be bothered to repair it again.
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Old 11th March 2018, 20:35   #2
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Quote:
Originally Posted by Randyjim View Post
Good evening readers!

I've been out this afternoon to do the routine maintenance checks, and had to top up the coolant a little. The o-ring at the bottom of the banana pipe is the source of the leak and not for the first time.

I thought I was doing well with the viton O-ring and molykote 111 combo, they seem to have lasted about 9 months this time, but no such luck.

When I first changed the thermostat (failed open, but not leaking), I found a significant scored mark on the side of the bore on the block which I rubbed back as best as I could, but I'm worried it's left enough damage to be causing repeat failures.

Can anybody offer any advice on repairing the bore, or should I just fill it with silicone sealant if I can be bothered to repair it again.
Try tidying up the scored mark a bit more with fine abrasive.

The o-ring has a certain amount of squeeze built into it so a certain amount of wear is tolerable to an extent.
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Old 12th March 2018, 09:03   #3
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I thought I was doing well with the viton O-ring and molykote 111 combo, they seem to have lasted about 9 months this time ...
Hi Jim,

Like you I have had repeated ‘O’ ring failures after varying lengths of time but after a great deal of experimentation and analysis I think I may have found the answer: prevent movement.

Renew all four ‘O’ rings. It doesn’t matter whether you use Viton or MGR original parts. A lubricant of some kind is helpful to assist correct seating when the plastic parts are refitted. The key lies with the clips on the straight pipe. I spent a lot of time pondering over the purpose of these but I think I’ve worked it out. Ensure that both clips are pushed fully outwards so that each is in close contact with the water pump shrouding and the thermostat housing. This forms a rigid assembly without which it is possible for the thermostat housing to rock slightly. My theory is that it is this movement which is flattening the ‘O’ rings, introducing a leak which sprays upwards over the thermostat housing seam causing the innocent owner to be convinced that the plastic has split. It hasn’t.

In order to carry out this repair reliably and efficiently I recommend not using the keyhole method. It is also good practice to observe the torque setting of 18 Nm for the bolt securing the curved pipe and thermostat housing to the block.

Simon
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Old 12th March 2018, 09:43   #4
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Simon,

Surely the clips set on the straight pipe have little or no effect on the rear banana pipe, other that as you say, make sure the 18Nm tightness on the common hold down bolt?
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Old 12th March 2018, 12:54   #5
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All of the above steps have been followed. I even went to the length of replacing a good thermostat with the version that has the support lugs underneath. I even had to return one to the supplier as it didn't have the lugs as their ebay photo showed.

This was fitted last June/July with the front inlet manifold removed, all pipe bores well cleaned, using Viton O-rings and a generous smear of molykote 111. Clips were pushed out as far as possible and the bolt torqued correctly. The system was well flushed and refilled with non OAT coolant. All good after that.

I was put back on to OAT after a cam belt and (2) waterpump changes in September, and everythings been fine until the first signs of a leak yesterday.

I'm not sure what more I can do. If I rub back the banana pipe bore any more I'll need a bigger o-ring and a way to get the metal filings out of the block.
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Old 12th March 2018, 14:48   #6
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Surely the clips set on the straight pipe have little or no effect on the rear banana pipe ...
I agree that that is a logical conclusion Ken. The next obvious question is what makes Jim so sure that it was the curved pipe's 'O' ring which leaked?
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I was put back on to OAT after a cam belt and (2) waterpump changes in September, and everythings been fine until the first signs of a leak yesterday.
Were all the 'O' rings renewed on these two occasions Jim?

I now also have the thermostat with the supporting lugs so the same set-up as you. I hope that your experience isn't going to be a portent for me.

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Old 12th March 2018, 16:43   #7
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There are many problems with the plastic set up.
1. The thermostat housing often leaks from the housing, around the plastic weld. That weld at times is not water tight.
2. The plastic pipes and the curved pipe have a seam in the middle, along the length. They tend to split here, and can open under pressure, only to close again when cold. Exactly like the T-piece on the 1.8T.
3. The groove for the O-ring is squeezed against the aluminium bore, on the one side, and the base of the groove in the plastic, on the other. When new, the o-ring will have a certain amount of elasticity, which will be able to follow the heating and cooling of the engine, and thus seal, by maintaining a pressure all around.
When older, two things happen. The o-ring get square and looses elasticity, and the plastic base of the pipe bulges under pressure from the o-ring, and gets permanently deformed. Eventually the o-ring can no longer exert sufficient pressure, and the system starts to leak.

There is no good reason to use the two locks on the straight pipe. Once the pipe is in place, it will not move, as there is no pressure differential on the two ends of the pipe, iow, nothing is pushing the pipe one way or the other. The lack of the two locks would in any case have no bearing on the curved pipe, which is under discussion here. So that is just a distraction in this case!

O-rings can be had in many sizes. To compensate for rust or wear in the bore, make sure the bore in the aluminium is cleaned to bare metal, and look for an o-ring slightly thicker than what you have used, or, if you can't find that, then slightly larger in diameter, which will give extra material to compress the o-ring once installed.

The problem with plastics as mentioned above will however prevent any solution involving plastic from being permanent.

That is just a simple scientific fact!
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Old 12th March 2018, 18:55   #8
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The "original" factory fit thermostat + pipes + o rings fit for mine lasted 14 years and then it was the banana pipe that let go. I think that is a long way towards a good innings.
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Old 12th March 2018, 19:38   #9
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14 years is fabulous!!
Have you had your car from new?
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Old 12th March 2018, 22:47   #10
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The "original" factory fit thermostat + pipes + o rings fit for mine lasted 14 years ...
That says it all.

Simon
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