Joint leak on thermostat pipe

[3-Max]

The rigid plastic eblow pipe connecting the thermostat housing to the water pump.
I had a very small leak at the water-pump end joint. Took it off gave it a damn good clean, repainted it & fitted new O-rings. (Spigots were masked off for painting.)

Has made it so much worse.

New are O-rings are 27mm id, 2.5mm c/s Viton rubber. Made sure the grooves were thoroughly clean & free of debris.
I used the tiniest wipe of Vaseline in the sockets to help get it back on.

Which part/s did I get wrong?

 

[Jack Hammer]

As long as all your surfaces are good and there's no cracks then the o-rings are the culprit. Oversize will do it. AC o-rings can be used too. They have different sizes than conventional ones. If even that does not work there's always gasket maker silicone.

 

[3-Max]

@Jack Hammer Thanks.
I've ordered some 3mm c/s nitriles as nitrile seems more squishy than viton & I have info from elsewhere that 3mm viton will not fit. I'll look at AC o-rings if 3mm nitrile also don't fit.

 

[TK3333]

Are you using oem o rings? I just got some to do the same repair as mine just started leaking also.

 

[Dave.n.Shirley]

This is interesting, as mine has also been leaking ... I've just had it a few weeks, but noticed the slow leak after the first run. I wasn't losing a lot of fluid, but enough to have to top up the level every couple of runs. I appear to have stopped the leak for now . I used a jubilee clasp , a strip of rubber , and some loctite gasket sealant .... looks tidy enough, so I'm not for draining the system and replacing the 'o' rings yet, but will do it if I have to. I'd like to see though what 'o' rings you end up using.

 

[3-Max]

Mine are not Yamaha ones (the only place I could find them would have cost £15 ea! & been imported).
I don't know what the OEM ones are made from. The ones I removed feel like nitrile. I bought Viton ones which are def harder rubber. They are meant to be the same size, 27mm id & 2.5mm c/s & are to spec as close as I can tell. c/s is def good. (5 for £4.90 the nitriles are 5 for £1.90 - all these prices inc postage.)
I got those spec's from a list made by a member here ( @joksi ). It also stated 3mm c/s Vitons will not work - 2.8mm was the absolute max, which made me think that 2.5mm c/s nitrile wasn't doing a good job & Viton was the way to go - apparently not, for me.
I will update on progress.

Edit: Point to note - the O-ring I removed from the end that's leaking has an oval resting shape while the other one is still circular, I'm wondering if there is a slight flaw in the pipe molding.

 

[MaxMidnight]

Fowler of Bristol have them in stock, part # 9321027778 at £5.65 for a kit (pair?)

 

[one2dmax]

I only use OEM since they are not a common size. Sometimes you can get lucky with aftermarket one.

 

[3-Max]

Thanks guys.
Does anyone know what size OEM actually are then (if they aren't 27mm id 2.5mm c/s)?

Where I got to today. I stopped the leak.
Having thought about the oval shape of the old o-ring I (correctly) remembered that the flange of the pipe wasn't sitting square against the socket rim. This means that the pipe & ring will be slightly 'oval' relative to the socket (it is more apparent than this pic shows).


So I slackened the thermostat retaining bolts (see pic for those who don't where these are) & pulled the pipe out until there was an even gap all the way round. It's about 2.5mm (1/10"). The leaked stopped.


After a little trial & error I placed a 0.025" (0.64mm) washer as a shim between the thermostat housing & the engine casing. This was ONLY on the bolt nearest the camera (the one without the socket extension). Re-tightened both bolts & this maintained the gap. No leak. Not even a hint of one. Not even after running the engine for over 10min.


I'd be interested to hear from you guys with a leak if your pipe is sitting square in the socket (excuse the language).

I plan to make up something to fill that gap (prob washer based) as it's possible to still move the pipe around slightly in this set up (but still doesn't leak). Just for peace of mind. When I fit that I'll also try the 3mm c/s nitrile O-rings that arrived today.

 

[Mehrdad]

The rigid plastic eblow pipe connecting the thermostat housing to the water pump.
I had a very small leak at the water-pump end joint. Took it off gave it a damn good clean, repainted it & fitted new O-rings. (Spigots were masked off for painting.)

Has made it so much worse.

New are O-rings are 27mm id, 2.5mm c/s Viton rubber. Made sure the grooves were thoroughly clean & free of debris.
I used the tiniest wipe of Vaseline in the sockets to help get it back on.

Which part/s did I get wrong?

View attachment 88164

I used oem orings and gray JB-weld gasket maker and its perfect!