Replacing coolant flanges

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rosie
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Replacing coolant flanges

Post by rosie »

I have a couple of leaks in my cooling system and need to replace these two flanges:

https://www.heritagepartscentre.com/uk/ ... -ring.html

https://www.heritagepartscentre.com/uk/ ... -ring.html

Just wondering if anyone’s done this, and where I’m going to come unstuck. Everything looks really rusty and I’m apprehensive about whether the nuts will come undone. I’ve got a few days to soak them in WD40 while I’m waiting for parts to arrive.

Do I just disconnect one of the bottom hoses to drain the cooling system before I start?

Anything I need to know before I start so I don’t end up with a pile of broken rusty metal where my car used to be!?
coolant flange smaller.jpg
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Re: Replacing coolant flanges

Post by GT_II »

I doubt the screws will have seized, as they are not particularly exposed to salt, though I've not had to remove those particular flanges. If they don't move when you try to undo, sometimes tightening them a fraction first to loosen them can reduce the risk of stripping the head while repeatedly trying to undo them.

To drain the coolant, I found it best to loosen the screws holding the thermostat housing flange and drain from there, which allows the coolant to flow past the thermostat when it is closed. If you do, it would be worth having a new thermostat seal handy, in case the old one doesn't reseal.


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Re: Replacing coolant flanges

Post by mark1gls »

If you remove the thermostat housing at the bottom of the water pump and it’s the plastic type buy a new plastic housing as they never seem to seal again.

It looks like this and hopefully will come with a new rubber o ring.

https://www.ebay.co.uk/itm/403444990274 ... R5KimMvHYg


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rosie
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Re: Replacing coolant flanges

Post by rosie »

Thank you guys 🙂
I got sidetracked by electrical problems so only came back to this today.

The new flanges came with an O ring fitted into the groove. When I removed the old flanges they seemed to have additional sealant on the face of the joint, and around the outside of the flange. I’m not sure whether this was from a previous bodge, or whether I should have used sealant rather than just relying on the O ring. Any idea please?

I cleaned up the engine where they attach with fine wire wool as there was a bit of scale and old sealant there so presumably the O ring will be making sufficient contact to provide a good seal? Haven’t refilled the coolant yet as I thought I’d check whether I’d done it wrong first!

Also, regarding the smaller flange on the left of the picture, I forgot to note which way up it sits when I took the old one off. There didn’t seem to be an obvious answer, but it is shaped in a way that suggests there’s a right way and a wrong way. Please can anyone confirm whether the flat edge is at the top or the bottom?
flanges resized.jpg
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Re: Replacing coolant flanges

Post by GT_II »

New O-rings shouldn't need sealant. Sealant is often used when an aged seal is disturbed but not replaced, so I'm guessing those parts have been refitted in the past. A high temperature sealant would be needed I would have thought in that case.

It looks as though one of the fixing holes on the smaller flange is off centre, I guess to allow access to the screw head. If so, hopefully you'll be able to figure out which way up it goes by studying the position of the screw holes on the mounting block, or perhaps, if there is good enough access, by mounting it loosely first one way and and then the other, while checking the alignment of the tubes at the interface with the block.


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rosie
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Re: Replacing coolant flanges

Post by rosie »

Thanks.
Ok, I think I get what you mean about the fixings. I’ll pull the hose off again and check that the central tube lines up properly. Hopefully I put it on the right way round already. It’s 50/50.
Thank you for your help. I really appreciate the time and help I get here.


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Re: Replacing coolant flanges

Post by mark1gls »

No sealant should be used or needed as the Oring should seal it and you’ve done the right thing with cleaning up the surface.

I just went out to check which way the flange goes but forgot I changed mine for an early type metal flange but I think the flat bit goes on the bottom as that’s where the metal coolant pipe fixes to the stud..?


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Re: Replacing coolant flanges

Post by GT_II »

mark1gls wrote: Thu Sep 14, 2023 10:37 pm I think the flat bit goes on the bottom
Correct, just checked on mine


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rosie
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Re: Replacing coolant flanges

Post by rosie »

Thanks so much for checking. That saved me having to undo it all.

Good news- I put it on the right way up.

Bad news - two of the three switches that sit in the other flange are leaking. Presumably the O rings are to blame and I ought to replace all three while I'm at it.

I’ve found these options on VW Heritage

https://www.heritagepartscentre.com/uk/ ... 5-65c.html

https://www.heritagepartscentre.com/uk/ ... -20mm.html

https://www.heritagepartscentre.com/uk/ ... start.html

https://www.heritagepartscentre.com/uk/ ... 90-316-802

but I guess I probably need to drain the coolant out again so I can remove the switches and double check the parts numbers. Not sure whether to just replace the O rings, or to get new switches.


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Re: Replacing coolant flanges

Post by GT_II »

The sensors likely don't come with seals. The part number for the seals is N90316801. Look to be around a couple of £ each from VW. Use a silicone oil or similar to make sure the seals seat properly when the sensors are fitted.


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rosie
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Re: Replacing coolant flanges

Post by rosie »

I’ve been trying to find the seals. They’re out of stock at VW Heritage where they cost a quid. Everywhere else wants between £5 and £20 for one!
I’m trying to get them today/tomorrow because my MoT is due next week and I still need to get the car to a garage for more work before that.
As an emergency measure I’ve ordered some plugs which come with the seals from Amazon for £7 a piece, but if you know of anywhere that has them available quick and cheap I’d be happy to hear about it. My local dealership wants £6 each for them!

I live a cycle ride away from VW Heritage - annoying they’ve run out.


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rosie
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Re: Replacing coolant flanges

Post by rosie »

I wonder should I have used silicone oil when fitting the flanges as well?


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Re: Replacing coolant flanges

Post by GT_II »

The flange seals will be fine as they just compress against the block The sensor seals look as though they have to slide in the gap between the sensor and the flange tube so lube definitely helps to seat them properly. Dilute washing up liquid is another alternative, or even just water, but not quite so effective.


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rosie
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Re: Replacing coolant flanges

Post by rosie »

Thanks. I’m cycling past Halfords later so will grab some then.


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rosie
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Re: Replacing coolant flanges

Post by rosie »

If anyone else is replacing these the parts numbers are:
Red - 251-919-369B
Black - 251-919-501A
Grey - 191-919-369B

Plus the O ring seals with the parts number mentioned upthread.


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