Alternative plastic kv6 thermostat longevity

[Greeners]

Originally Posted by marinabrian

As pointed out earlier, failure of the CDU3858 O Rings is a common problem, whether this is due to mechanical fatigue or chemical attack is a matter of opinion.


Brian

Eaten by OAT perhaps ????

[SD1too]

Originally Posted by Greeners

Eaten by OAT perhaps ????

David,

That's a favourite theory when anything different (OAT) is viewed with suspicion. However, when the facts alone are considered there are an awful lot of engines using OAT which do not suffer from shrunken 'O' rings. The logical explanation of that is that it is something else which is responsible. I am currently testing my theory that it might be incorrect fitting of the straight pipe clips, but we'll have to see.

Simon

[Randyjim]

I think there's some unreliable o-ring suppliers out there too. I've fitted 3 sets to my ZT190 in just over 2 years of ownership.
The 1st set went in with a new thermostat when mine failed open (no leaks at all).
The first set failed at the base of the curved pipe, and then later at the thermostat end of the short pipe after about 3-4 months.
When the second set started to go at the waterpump end of the straight pipe after 6 months I started getting quite fed up, but battled on for 6 months with frequent topping up.
I sourced some Viton O-rings and a sachet of Molykote 111 and tried again.

The second set I removed were split supply. Some came from my tool box, but were bought from Rimmer Bros some years ago for my coupe. The others came in an MGR bag from the same supplier as the new thermostat previously fitted. I can't recall which way around they were fitted, but the leaking ones were noticeably flatter. The others were slightly greyer, but still round and apparently sealing. I've never removed a pinched/split o-ring from my car, only degraded ones.

The latest Viton set are holding strong so far and I've never had a leak from the thermostat housing. Fingers crossed.

[dbt01]

If you do it the 'proper' way instead of keyhole, you can take a look at the journals into which the 'stat, elbow and cross-pipe fit. Cleaning them up really well is essential I think to ensure a good seal on the O-rings, at least avoid a bad one. I always do it, just 20 minutes extra work. I use Molykote too (but the 55 O-ring grease), which helps. All I can say is that I have only 3 needing changing in the 250,000 kms on my 3 V6's and never once because of the O-rings, always because of elbow cracking (2) and/or thermostat case separation (also 2). Maybe I'm just damned lucky!

David

[DMGRS]

Personally, I don't like the keyhole method as it's too easy to miss some debris left in the coolant orifice into the head, and easy to 'nick' and O Ring when pressing components home.

We've had a good degree of success with the 'reinforced' thermostats we have here - they're made by the OE supplier and a thick layer of steel epoxy resin is applied around the joint to stop any movement that'd allow failure.

The design of the whole assembly isn't my favourite, and is badly flawed (IMO of course) - personally I would have rather the Kaiser item was a lot more widely available as this seems to be a good solution to the problem.

[Randyjim]

Originally Posted by DavidBytheway

If you do it the 'proper' way instead of keyhole, you can take a look at the journals into which the 'stat, elbow and cross-pipe fit. Cleaning them up really well is essential I think to ensure a good seal on the O-rings, at least avoid a bad one. I always do it, just 20 minutes extra work. I use Molykote too (but the 55 O-ring grease), which helps. All I can say is that I have only 3 needing changing in the 250,000 kms on my 3 V6's and never once because of the O-rings, always because of elbow cracking (2) and/or thermostat case separation (also 2). Maybe I'm just damned lucky!

David

I think you've been lucky with O-rings David, but not the plastics.

The first 2 times, including the original thermostat change, I went keyhole, but I did take time to clean out the bores for the thermostat and the elbow pipe, including rubbing down with some fine sandpaper. The curved pipe was a NAUGHTY WORD-NAUGHTY WORD-NAUGHTY WORD- to remove and probably ended up in about 8 pieces plus some dust.

The most recent work was done with the front manifold removed, so I cleaned up the water pump end bore too. I also changed the thermostat to the type with the supporting lugs and moved away form OAT coolant. I tried everything, and so far it's working!

It may be that something else I changed has been effective other than the o-ring change, but there's no denying when I removed the previous set they had all deteriorated in slightly different ways, suggesting a range of different rubber quality had been used.

I think there's issues with both the O-rings and some of the plastic quality out there and there may be a bit of luck required to get a good fix which is a shame.

I'm also now back on OAT after a cambelt & water pump change and everything in the V is still good and dry. The current set of rings actually outlasted the new waterpump though, that gave up after 500 miles!

[Arctic]

I found this thermostat to be really good and would not use any other, that is my own personal opinion, I found it to be more stable than others without the lugs.

Combine it with making sure that all the coolant orifice into the head is clean, add some rubber grease and you should be good to go.

https://www.ebay.co.uk/itm/MG-ROVER-....c100011.m1850

[trikey]

Originally Posted by Arctic

I found this thermostat to be really good and would not use any other, that is my own personal opinion, I found it to be more stable than others without the lugs.

Combine it with making sure that all the coolant orifice into the head is clean, add some rubber grease and you should be good to go.

https://www.ebay.co.uk/itm/MG-ROVER-....c100011.m1850

That’s the supplier I use too, always genuine stock, the keyhole method works fine, just ensure that everywhere is clean and always lube the o rings.

[Randyjim]

I used that supplier too, so I expect that is the 'stat I have fitted. I ordered through eBay based on the picture, but was sent an unsupported OE part instead. Luckily he still had one of the parts with support lugs and was happy to send that out as a replacement, so I can't fault the service. The picture on eBay also got changed after I'd contacted him, so now that it's back I guess this style must be back in stocks again.

I'd suggest anybody ordering one shiuld send a note to the seller Confirming you want the support lugs though, just to be sure.

[SD1too]

Originally Posted by Randyjim

I'd suggest anybody ordering one shiuld send a note to the seller Confirming you want the support lugs though, just to be sure.

Simon