KV6 Thermostat question (views appreciated)

[aguy]

I asked this as a post in another thread but never got a reply.

We know the 'plastic' thermostat housing is prone to failure and loss of coolant.

My question is what is the average life of these once replaced. ( how long is a piece of string is NOT helpful) Also the question is about 'plastic' and not for those who have managed to source aluminium.

Is mileage a factor? do long journeys have any more effect on the housing than shorter stop start runs?

I had mine replaced recently and I have seen some really good threads on here about how to keep an eye on the engine 'V' for leaks and how these can be replaced using 'keyhole method' etc., but nothing on how long we might expect to solve a leak problem for, once this work is done?

I just thought if we could get a few people to post their experience of life for this part it would give us some sort of an average, thus allowing us to consider changing the thermostat at intervals as a preventative measure.

[chris75]

My original lasted about 80k miles . I assume the replacement is going to last about as long , so you might not get much data on repeat failures

[trikey]

The plastic used is glass filled nylon, 30% glass if memory serves well... It is a hygroscopic material (absorbs moisture) nylon can become brittle if it does not take in moisture over its lifespan.

Obviously as water passes through it, this is good for the life of the moulding. Now, this is going to start the old argument once again, but, the use of oat antifreeze, in my experience, significantly reduces the life of the plastic moulding, I have been able to squeeze and break a couple of the elbow pieces when replacing thermostats, I have only seen this on cars where oat has been used.

The stat on my old v6 failed at 140.000 miles, that was an original part, I have had customers cars in that needed a stat at 70.000 so it's a bit like a lightbulb really!

[aguy]

Originally Posted by trikey

The plastic used is glass filled nylon, 30% glass if memory serves well... It is a hygroscopic material (absorbs moisture) nylon can become brittle if it does not take in moisture over its lifespan.

Obviously as water passes through it, this is good for the life of the moulding. Now, this is going to start the old argument once again, but, the use of oat antifreeze, in my experience, significantly reduces the life of the plastic moulding, I have been able to squeeze and break a couple of the elbow pieces when replacing thermostats, I have only seen this on cars where oat has been used.

The stat on my old v6 failed at 140.000 miles, that was an original part, I have had customers cars in that needed a stat at 70.000 so it's a bit like a lightbulb really!

That's an interesting one Andy and I certainly don't want to open any old arguments.

When you did mine for me I noticed the actual thermostat housing looked like new, it was the elbow and straight bits that were badly "corroded" I say corroded because that's what it looked like. So it is possible I suppose that it's a chemical reaction in the 'plastic' coupled with the heat and if that's the case the type of coolant could indeed have an influence.

Mine certainly wasn't a case of the housing splitting on the join as so many have found.

[genpk]

I have seemed to get around the 70,000km point before they start leaking,always the same spot,the ultrsonic weld, although got 100,000km out of one.
I have replaced one of my cars with Kaiser's aluminium one and about to do the other cars as well.
I did manage to examine what was going on with the welds cracking and found some comments from some ex MGR guys as to the whys and wheres re the plastic thermostats failing.
From what I gather MGR treated the plastic thermo like a service item which should be changed at longer services.
I believe one of the engine guys mentioned that MGR were looking at placing some sort of support bracket for the long radiator hose due to the issue and assessed the pull weight of the hose with water in it was the primary cause of the issue, but MGR never implemented the bracket.
Given that prompt,you can plainly see the issue re the cracking of the welded join when you watch the engine movement when rev'd.Basically,the long radiator hose full of water (weight) is pulling on the top of the thermo housing,add heat and vibration and over time the weakest point cracks.
I ended up getting a round house water down pipe bracket and supported the hose around the bleed pipe area and bolted it to the engine lift bracket.
I might add that was the car that has done 100,000km on the one thermo.
My guess is it definately extends the thermos life as it stops the pullling and vibration.

[neilll]

My first one went at about 36k and the second at around 84k. Have got one of Kaisers alloy ones to fit purely for piece of mind (any one fancy doing it for me-willing to pay). I would say from my experience between 30-40k and your living on borrowed time.
Neil

[DMGRS]

I'm on an original here in the ZS180, 89,000 miles and 12 years old. It's starting to open early though.

[aguy]

Originally Posted by DMGRS

I'm on an original here in the ZS180, 89,000 miles and 12 years old. It's starting to open early though.

Yes well I suppose there's a positive point here Mat, maybe we should all buy a unit from you to keep in the glove box.

[SD1too]

Originally Posted by aguy

We know the 'plastic' thermostat housing is prone to failure and loss of coolant.

I've examined and tested my plastic thermostat housing on both occasions that it's started leaking. Here's a photograph of what it looked like the first time:



Obviously a crack in the seam wouldn't you agree? Err ... no, it wasn't. The seam was watertight. It was the 'O' ring, and the second time it happened it was the 'O' ring again. Look at it's profile:



You can see how flat it is, offering little sealing ability.

Originally Posted by genpk

From what I gather MGR treated the plastic thermo like a service item which should be changed at longer services.

There is no evidence in the MGR service schedules to support that idea.

I believe one of the engine guys mentioned that MGR were looking at placing some sort of support bracket for the long radiator hose due to the issue and assessed the pull weight of the hose with water in it was the primary cause of the issue, but MGR never implemented the bracket.

That's an idea worth pursuing.

I might add that was the car that has done 100,000km on the one thermo.

Unfortunately that mileage isn't high enough to prove your theory.

Originally Posted by trikey

... the use of oat antifreeze, in my experience, significantly reduces the life of the plastic moulding, I have been able to squeeze and break a couple of the elbow pieces when replacing thermostats ...

What we have to ask ourselves is, is that a valid test? Were the glass reinforced nylon parts chosen to withstand compression forces in normal use? Also, did you squeeze a brand new part as a control for your experiment?

On the subject of OAT, I now have a leak into my 'V' for the third time! The indication is that it's an 'O' ring again despite me fitting EPDM all round, which are supposed to withstand steam and antifreeze! So, when I once more replace the 'O' rings, I'm seriously considering refilling for the first time with non-OAT antifreeze to put it to the test.

Simon

[jn12]

I think they are just as Trikey has said, like light bulbs!

I have had one leak around the joint and run cool after 9 months of fitting. O rings have always looked ok upon removal.

I have taken Brian's advice and now use Blue coolant.