Did a dodgy thermostat kill my engine ??

[ghost123uk]

OK, I'll try to be brief.

• Fitted the engine ~8 years ago, was a re-con, it's been A1 up till now.

• A month ago, on an urgent trip, it burst a water hose right open.

• I was in a hurry, so quickly fixed it at the roadside, re-filled with water, and very carefully drove the last 6 miles.

• It boiled up and needed more water twice on that short trip, also chucking lots of water into the top up tank, overflowing it.

• Drove it to our "Jim The Painters" place to remove the engine. It burst another water pipe on route = towed it the last 3 miles.

• Used a head gasket test sniffer = proved positive.

• Removed engine and arranged a used replacement.

• Important bit = for some reason I suspected the thermostat, I tested it in a pan of water on the cooker, it seemed OK but I didn't measure temps.

• Fitted replacement engine.

• Fired engine up, all good for about 20 mins at a fast tickover, then started producing big gollops of bubbles in the main coolant tank (cap off).

• Started me thinking, a leaky head gasket wouldn't pressurise a system so fast as to burst hoses, the Dalek (in good nick) would vent it. (comments??)

• Started suspecting water was boiling in a head, and it was steam over pressurising the system.

• Checked ALL pipes for blockages (note the current thread on bleed rail blockages) - mine were all clear.

• Back to the thermostat = Both Jim and I commented that, though the engine felt hot enough (~20 mins tick over), the pipes to the rad were still cold.

• To test the hypothesis that the stat might be dodgy, I drilled lots of holes in it's top plate (because it won't seal with no stat fitted).

• Bled it AGAIN (I'm getting a dab hand at that)

• Fired up again, left it at a fast tickover until the temp gauge finally reached "normal" and the rad fan eventually kicked it (~30+ minutes).

• No sign of any bubbles at any temperature, right up to "normal" (so I don't think it was a cracked head opening up).

• Since then I have done about 80 miles, including some 30 mile runs, with the stat drilled, with no coolant issues at all.

This morning I have taken delivery of a new stat and will be fitting it in a short while.
I will then, very nervously, take it for a long test drive (after initial checks).

I'm wondering if a dodgy stat caused the pressure build up on the original motor, and my haste to get where I was going, caused a blown head gasket or cracked head (though it didn't feel / look / sound overheated, but maybe the addition of cold water was not good).

What do you reckon to all that folks ?

[what2do]

I'm not qualified to pass comment but I sincerely hope this is the start of a good run of luck for you John.

[itchyfeet]

I think thats it John.

I wonder how many others are driving around with ancient thermostats.

I hope you got a decent quality new one from Brickwerks

[ghost123uk]

I think thats it John.

I hope so, but the "pan test", though not very scientific or accurate, but it did lead my to think it was OK (comments invited).

I wonder how many others are driving around with ancient thermostats.

I hope you got a decent quality new one from Brickwerks

Ah, now, the stat was only about 2 years old, and it WAS one from Brickwerks. It still looked like new.

The one I have just bought came from a local motor factors.



Just waiting for the rain to cease before going out to fit the new one.

[petethefeet]

I have limited experience of one make of thermostats as I worked as a development engineer for them for 5 years.
Most wax fitted thermostats work by the expanding wax forcing a pin (piston) out of a small sealed copper container, between the pin is a rubber boot (this is on most but not all thermostats), in time water gets trapped in between the boot and the pin this causes the to 'open early' causing a cold running system and your heater not working.
Only relatively few thermostats failed by failing to open at all but it did happen if the wax escaped by the copper container splitting (material fault) or the frame of the thermostat failing.
Re. the pan test, this needs to be done very slowly to get a valid result, try to hold the water temp at the temperature stamped on the thermostat and allow the thermostat to warm through, the valve should then open by 0.2 mm to be classed as the 'start to open point' (STO)

[Highroller]

John,
It would probably be wise to get another sniff test done as this could one way or another eliminate a lot of your questions.

FYI, on your last technical thread I mentioned that I had identical issues and I was also going to get another sniff test done until I burst the bleed screw in the radiator. Anyway, I eventually got one done and it was negative for combustion gasses although I wasn't there to witness it. I will be watching this thread with interest as I definitely had water boiling in the heads creating a lot of steam which interestingly didn't vent out the header cap. I ended up replacing the whole thermostat housing from Brickwerks and a thermostat with one from a motor factors. I have done at most a 30 mile round trip with no overheating issues although I did feel that there was still a lot of pressure in the system when I released the cap after I got home.

Anyway, Good luck and I hope that you have got to the route of the problem and it puts an end to your will I or wont I dilemma.

[itchyfeet]

I drilled lots of holes in it's top plate (because it won't seal with no stat fitted).

Stat has two functions, it hold the bypass tube open when stat closed and closes the bypass tube when stat open, anorther reason not to remove it ever.

http://wiki.club8090.co.uk/index.php/Pe ... em_diagram" onclick="window.open(this.href);return false;


Sorry I missed the bit where you said you tested it, if it was a new one from brickwerks 2 years ago and tested then it does seem odd that it is faulty, I suppose if you had some air in the system on the second engine it could have led you to believe it was faulty, ( as stat opens trapped air above stat will come through ) you must have had doubts about it and maybe you came to the wrong conclusion.

Origional engine may have been a genuine blown compression seal that burst the hose open and not the stat.


re sniff test, how long will hydrocarbons stay in coolant?
I assume you reused old coolant?

[marlinowner]

Have you checked the pipe between the dalek cap and the overflow tank? Mine was blocked which meant the cap couldn't vent and the system overpressurised.

[ghost123uk]

re sniff test, how long will hydrocarbons stay in coolant?
I assume you reused old coolant?

Goodness no. The coolant (read "water") has been chucked out by blown pipes and by me removing and re-fitting engines etc etc many times in the last couple of weeks. I won't be putting the red stuff in until I am fully satisfied that all is well.

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All interesting stuff above, thanks for all your input, though I have to say I am getting really sick of messing about with all this.

I have just completed a ~15 mile run, up to temp, with no issues. This was "round and around" the village, I didn't want to go too far from home in case it burst another hose !!!!!!!!!!!!!! The radiator was hot, top to bottom, (well cooler at the bottom), on my return home.


It did seem to take quite a while for the stat to open, (or that could be me being paranoid) and the gauge settled at just over half way, Although the return pipe into the expansion tank seems to flow in a lively enough manner when the motor is running (obviously) and, when I examined the water pump, it looked ok, I keep wondering if there is a "flow" problem. All the pipes have been very thoroughly flushed and tested by the way.


I am just going to have a bite to eat, then take it for a longer drive.

[ghost123uk]

Have you checked the pipe between the dalek cap and the overflow tank? Mine was blocked which meant the cap couldn't vent and the system overpressurised.

Yes, replaced it actually.

And I have two proper blue caps here, they both "quack" - I have had them both on at one time or another.

If, as seems possible, even likely from what others have written above re the way thermostats are likely to fail, maybe I have been barking up the wrong tree, but that then leaves me wondering what the heck was going on (lets hope it's not still going on).

It would probably be wise to get another sniff test done as this could one way or another eliminate a lot of your questions.

Not currently getting any bubbles in the tank, so thinking this motor is OK in that respect.

Anyway, Good luck and I hope that you have got to the route of the problem and it puts an end to your will I or wont I dilemma.

Thanks.

[ghost123uk]

Well just put another 40 miles on it, fast A roads and country lanes, no issues. Coolant stayed at a steady level, no bubbles or owt.

Not counting my chickens yet though, I will use over the next few days and put at least another 100 miles on it, just to make sure it's all good.

However, it will be for sale as soon as I am satisfied that it is fully OK.

[itchyfeet]

Great news about the engine, sad to see you sell it.

[ajsimmo]

Well that sounds very encouraging!
I think it was possibly an air lock that just wouldn't shift first time out. The drilling of the stat may be a red herring, as just the act of disturbing it, then refilling and bleeding may be what cured it. Or maybe the drill holes just allowed a little more flow from cold to shift the air. After all, this is why you bleed it at revs, to get that pump really pumping, and shifting those stubborn bubbles.
John, when you said the replacement engine was also no good, I thought you meant that the water jacket seals were leaking! I must have misunderstood.
As for pressurising, I had a client in who'd just bought a van (late dg), and was coming straight to me for lpg.
He'd driven 200 dual carriageway miles before it had blown out so much coolant that it got hot. It was a compression seal leaking a tiny bit. Seemed fine on 20-30 mile A/B-road tests, until you used high revs for any length of time then it pressurised. I sold him a good used DG (out of my own van!) to get him on the road cheaply, then did a reseal on his engine (which is now running fine in a van on the IoW). There was a very small track mark on one seal ring, and signs of a tiny divot or screwdriver gouge on the head under the ring. Can't say for sure if that was it, but I think it was.
The point of that story is, road test at speed, and keep road testing (preferably for the next 10-20 years!).

[Mocki]

so, im a little confused.... you have taken the engine out that popped the water pipes, and put another one in, which had a thermostat issue ?

assuming if i have read and understood this right , you swapped the thermostat housing over to the replacement engine >>

so the van is for sale with another engine in it recently fitted ???

[itchyfeet]

^^ yep old engine blew a compression seal
replacement engine probably just had an air lock leading John to think it was duff.
It seems fine now thermostat probably a red herring ( it was swapped from origional engine to replacement)