Hi Al, On the 1.9 M43 engine (single overhead cam), year 2000, am I right in thinking the connector plug on the side of the plastic thermostat housing is a form of heater to help keep the thermostat open? A friends Zed overheated, the RAC said on removing the thermostat that it had stuck shut and so removed it breaking the electrical connections and refitted the housing minus thermostat. Told her it should be o.k now to drive home, needless to say it boiled up as they presumably mis-diagnosed a blown head gasket. In my experience thermostats usually fail in the open position, is this a correct assumption?
Regards BB
Thermostat Query
Re: Thermostat Query
In a DIY capacity, I have changed a fair few over 40 years of motoring and I have only ever experienced ones sticking open (including the Z) which was evidenced by the car in question running too cold. However, I have no technical data/confirmation that they can't stick in a closed position. My Z3 (M44 1.9) hasn't got an electrical connection attached to the thermostat housing but I am aware that some cars do have an integrated coolant temperature sensor or similar (e.g. Vauxhall ecotec engine) - not sure that it acts as a "heater"? 
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therealdb1
- Joined: Tue 25 Jun, 2013 21:47
- Posts: 263
Re: Thermostat Query
Thermostats can fail either open or closed. Trust me I have had both... Several times each!
Not sure about the 4 cylinder but my 6 pot has a heated thermostat.
Not sure about the 4 cylinder but my 6 pot has a heated thermostat.
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Mike Fishwick
- Joined: Fri 19 Jun, 2009 10:27
- Posts: 2093
- Location: Daglan, France
Re: Thermostat Query
What were the symptoms before the RAC man decided to gut the thermostat?
The electrically-controlled thermostat was introduced to permit the ECU to regulate coolant temperature between very close limits, so reducing exhaust emissions and fuel consumption.
Unlike old British cars, the electrically-controlled thermostat - as with some older wax thermostats used by german manufacturers - has two valve plates, which control two inlet/outlet orifices, one for the radiator and the other for the engine.
Removing this type of thermostat will allow the pump to circulate coolant without it being forced through the engine and then to the radiator and the engine will therefore overheat. If you look at the thermostat you will see both valve plates - one in the plastic casing, and the other on the end of the control assembly.
I would have thought that RAC people would know about this . . .
I would advise fitting a new thermostat before suspecting head gasket problems - go one step at a time, and do not make suppositions.
The electrically-controlled thermostat was introduced to permit the ECU to regulate coolant temperature between very close limits, so reducing exhaust emissions and fuel consumption.
Unlike old British cars, the electrically-controlled thermostat - as with some older wax thermostats used by german manufacturers - has two valve plates, which control two inlet/outlet orifices, one for the radiator and the other for the engine.
Removing this type of thermostat will allow the pump to circulate coolant without it being forced through the engine and then to the radiator and the engine will therefore overheat. If you look at the thermostat you will see both valve plates - one in the plastic casing, and the other on the end of the control assembly.
I would have thought that RAC people would know about this . . .
I would advise fitting a new thermostat before suspecting head gasket problems - go one step at a time, and do not make suppositions.
A Z3 is not just for Christmas - it's for life!
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bentley-boy
- Joined: Mon 28 Oct, 2013 19:35
- Posts: 261
Re: Thermostat Query
Excellent response, thanks Mike. I had wondered if the 'stat' was part mechanical/part electrically heated. Other sites suggests the 1.9 was mechanical and the bigger engines electrically heated. I fully take your point about the two valve plates, in the cold state coolant is directed around the engine for rapid warm up, a hot engine then allowing the 'stat' lower plate to move and close off the by-pass route around the engine and forcing it through the radiator and back through the engine. Presumably putting this type of 'stat' into boiling water will show no signs of it opening without the electrical current.
The lady in question pulled up when she noticed steam but not recalling what the temp gauge indicated. RAC said it could be a head gasket or a stuck 'stat'. After removing the 'stat housing he said it was jammed shut and so he removed the 'stat' innards (breaking the electrical wires to do so) and refitted the housing and topped up with water telling the lady she should be o.k to drive the 18 miles home (on a suspect head gasket!!). Some short while later the car started steaming with full gauge deflection. In an attempt to get to safety she moved over the traffic lanes as the engine stopped (seizure?). RAC called again and a different outfit relayed her home.
I looked at the car the next day and put a watering canful into the engine bleeding the system at the same time. Ran the engine to normal temp where I noticed water/steam emanating from the expansion tank lower seal joint (no sign of a cracked exp' tank). Switched off and after the pressure had relieved itself I topped up with hot water and ran the engine again with pressure cap removed to look for signs of bubbling which immediately showed up as excessive bubbling in the exp' tank, presumably it was not at the 100+ degrees it would boil at atmospheric pressure. Didn't look to see if steam from the exhaust but it certainly used the water.
So just to recap, the 'stat is purely electrically heated then and removing it would allow coolant to bypass the radiator and circulate around the engine instead as in warm up mode?
BB
The lady in question pulled up when she noticed steam but not recalling what the temp gauge indicated. RAC said it could be a head gasket or a stuck 'stat'. After removing the 'stat housing he said it was jammed shut and so he removed the 'stat' innards (breaking the electrical wires to do so) and refitted the housing and topped up with water telling the lady she should be o.k to drive the 18 miles home (on a suspect head gasket!!). Some short while later the car started steaming with full gauge deflection. In an attempt to get to safety she moved over the traffic lanes as the engine stopped (seizure?). RAC called again and a different outfit relayed her home.
I looked at the car the next day and put a watering canful into the engine bleeding the system at the same time. Ran the engine to normal temp where I noticed water/steam emanating from the expansion tank lower seal joint (no sign of a cracked exp' tank). Switched off and after the pressure had relieved itself I topped up with hot water and ran the engine again with pressure cap removed to look for signs of bubbling which immediately showed up as excessive bubbling in the exp' tank, presumably it was not at the 100+ degrees it would boil at atmospheric pressure. Didn't look to see if steam from the exhaust but it certainly used the water.
So just to recap, the 'stat is purely electrically heated then and removing it would allow coolant to bypass the radiator and circulate around the engine instead as in warm up mode?
BB
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Mike Fishwick
- Joined: Fri 19 Jun, 2009 10:27
- Posts: 2093
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- Location: Daglan, France
Re: Thermostat Query
I have never seen one in the metal, but the 'normal' thermostat which was fitted to the 1.9 140 bhp engine - the M44 - was probably a two-late type anyway, as used on a Golf GTI etc. People tend to assume that things such as this are always what they are familiar with!
I think that the 'electric' thermostat still uses a wax cartridge, which is controlled electrically against the spring pressure. It was used on the six-cylinder engines from September 1998, and on the later four cylinder engines.
A de-gutted thermostat - or one with broken plastic lugs (common on pre-2000 cars) will allow coolant to flow in the block and in the radiator, so sometimes causing a hot engine and a cool radiator.
It is now difficult to tell if the original thermostat had broken lugs, so I would still advise replacement of the thermostat as a first step, and then see how things go. The bubbling coolant could well be a sign of head gasket problems, but it could also be signs of air in the system. As a second step therefore, bleed the engine properly, with the cap in place, by using the bleed screws, and top the engine up frequently, keeping a log of the amount of coolant used.
Hope the engine was not siezed, as that would not do the bores any good at all.
Thermostat with broken plastic lugs
I think that the 'electric' thermostat still uses a wax cartridge, which is controlled electrically against the spring pressure. It was used on the six-cylinder engines from September 1998, and on the later four cylinder engines.
A de-gutted thermostat - or one with broken plastic lugs (common on pre-2000 cars) will allow coolant to flow in the block and in the radiator, so sometimes causing a hot engine and a cool radiator.
It is now difficult to tell if the original thermostat had broken lugs, so I would still advise replacement of the thermostat as a first step, and then see how things go. The bubbling coolant could well be a sign of head gasket problems, but it could also be signs of air in the system. As a second step therefore, bleed the engine properly, with the cap in place, by using the bleed screws, and top the engine up frequently, keeping a log of the amount of coolant used.
Hope the engine was not siezed, as that would not do the bores any good at all.
Thermostat with broken plastic lugs
A Z3 is not just for Christmas - it's for life!
Re: Thermostat Query
i would remove the rocker cover and check the head bolt at the back of the engine by the exhaust. They are a common break. My wifes had snapped and was lying alongside the rockers, with a nicely blown head gasket. M43 engine.
Other checks I did first,
Take off the expansion cap with the engine cold. This gets rid of any residual pressure, Refit and start engine for 30 secs then switch off. Any new pressure on a cold engine is a good sign it is coming from the cylinders not heat expansion.
Also the hoses become less squashy and more rigid.
I had the oil level increase and was milky on the dipstick
Steam eminating from back of engine but not from exhaust, also rocker cover full of mayo.
see wifes journal at bottom of my post for photo's
Thermostat was fine but I swapped out it and the water pump anyway.
Other checks I did first,
Take off the expansion cap with the engine cold. This gets rid of any residual pressure, Refit and start engine for 30 secs then switch off. Any new pressure on a cold engine is a good sign it is coming from the cylinders not heat expansion.
Also the hoses become less squashy and more rigid.
I had the oil level increase and was milky on the dipstick
Steam eminating from back of engine but not from exhaust, also rocker cover full of mayo.
see wifes journal at bottom of my post for photo's
Thermostat was fine but I swapped out it and the water pump anyway.
Z3 2.8 Progress Journal (Mine)
Z3 1.9 Sport Progress Journal (Wifey's)
I have an element of 'M-styling' on my car, If that's a good enough reason for the manufacturers to adorn a 320 with the M badge, then its certainly a good enough reason for me..
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bentley-boy
- Joined: Mon 28 Oct, 2013 19:35
- Posts: 261
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Re: Thermostat Query
Thanks for the reply guys, good points and will have a look when the woman concerned decides she wants it tackling as I've heard nothing from her.
Regards all BB
Regards all BB
Re: Thermostat Query
I changed my thermostat just before the summer in May which was easy enough, you can just about do it with the fan still in place but once I had refilled the system the expansion bottle decided to leak so I would recommend changing that too if it had not been changed before.
Bleeding the system was a bugger though, I thought I had bled it enough until I went for a 180 mile drive the next day, when I checked the water before coming back home it was just varely visible in the tank, luckily I had the sense to keep a top up bottle in the car as a precaution, once I had topped it up and got home I left it to cool then checked it again and it hadn't gone down and hasn't lost any water since then...So bleeding is a long winded operation.
Bleeding the system was a bugger though, I thought I had bled it enough until I went for a 180 mile drive the next day, when I checked the water before coming back home it was just varely visible in the tank, luckily I had the sense to keep a top up bottle in the car as a precaution, once I had topped it up and got home I left it to cool then checked it again and it hadn't gone down and hasn't lost any water since then...So bleeding is a long winded operation.
