Thanks Teabelly
I hadn't realised that this could CAUSE further overheating.
The Thermostats I have been buing have been from the big Auto accessory chain, where all the boy-racers go (myself included - even in a Metro).
Anitfreeze mix was the same-brand, and I added water too it as per the ratio recommended.
D7
|
D7
The thermostats you took out, were they stuck open or shut ?
Did you test them (Put thermostat in pan of water and bring to the boil - you should be able to see it open)
mike
I have to grow old - but I don't have to grow up
|
The thermostats on modern engines are designed to "Fail-safe", ie in the open position.
To have 3 or 4 fail in the closed position is, to say the least, unusual.
If you run without, the engine will take a long time to warm up and will never reach the optimum operating temperature.
This will result in excessive fuel consumption, poor performance and eventually cylinder bore wear.The engine oil will become rapidly contaminated with moisture/condensation and you find "scum" inside the cambox/rockercover.
I would suggest that the problem could be due to some peculiarity with the coolant mixture or incorrect fitting (such as using the wrong thermostat housing gasket preventing the thermostat opening properly).
|
Lauriew,
Are you certain that modern thermostats fail 'safe'? I asked this question in this forum before but didn't get an answer. I was very familiar with thermostats about ten years ago and they definitely failed 'closed' in those days. These were as fitted to heavy-duty diesel engines but I feel sure were the same as fitted to motor car engines.
Regarding leaving out the thermostat, this can cause a lot of problems. Many (most/all?) modern thermostats control not only the main coolant passage but also the radiator by-pass passage. When one is open the other is closed. That is, when the thermostat opens the main passage, it blanks off the by-pass so that the coolant is forced to flow through the radiator. Without a thermostat in place, not only will the coolant take a long time to warm up but the temperature will then possibly continue to rise to the point of overheating because some of the coolant will be by-passing the radiator.
|
|
Buy a main dealer unit and try that perhaps?
|
|
|
During my younger days, I worked in the Engine Research dept of a well known international company. This involved the dynamometer testing of prototype automotive, industrial and marine engines. Most of these engines ran 24/7 at full throttle.
The temperatures (both oil cooler and water), was controlled using standard wax-type thermostats.These were very reliable.As I recall there were only two failures, and these "failed safe". According to the thermostat maker, this was a design feature. The test-beds were set up in conjuction with the engine maker regarding operating temperatures etc.
|
|
|
|
|
T-b - I'm not sure how a thermostat can do anything to limit pressure. The cooling system is a circuit, so all it can do is prevent circulation, it can't put the lid on anything (though the pump will try to help).
However I agree that if pressure were increased, that would prevent the coolant boiling and thus improve heat transfer.
|
I'm probably wrong here but I seem to recall that the thermostat in the Metro causes a certain degree of back pressure. Without this the flow of coolant to one cylinder is insufficient. I could be wrong, been known before, but this is one of those odd bits somehow stuck away in the old grey matter.
also unless I have misuderstood how a wax thermostat works, how can it always fail in one position ie open/closed. Surely (Shirley) it fails in whatever position it happens to be in? or?
|
FiF,
The thermostat has a spring holding the valve closed at low temperatures and a capsule containing wax which expands under heat to controllably overcome the force of the spring and open the valve.
The wax capsules are very reliable but when they do fail, usually by leakage of the wax, the spring simply holds the valve closed.
|
D7,
Important question...
How do you know all these thermostats have failed closed? Have you tested them all in a pan of water and proved they don't open towards/at boiling point?
MM
|
In my years of experience of thermostats in a number of different cars, I have come to realise that there is a lot more to them than simply on/of at the correct temperature. Other contributors have pointed out some of these factors, including the paradoxical one that omitting the thermostat can actually increase overheating.
I have also noticed that the internal designs vary, so that it can be important to get the right one, not just one that fits and has the correct temperature stamped on it.
For example, the degree of constriction varies, so even when fully open as intended, some models apply more back pressure or may be designed for a higher output waterpump.
I know from experience that removing the thermostat is not a cure for failing to rectify some other cause of overheating.
|
It was the earlier "Bellows" type thermostats that was prone to failure in the closed position. These are rarely used today as an equivalent wax type(more accurate and cheaper) will be available.
Regarding the original posting: I would suggest that the radiator pressure cap be changed after ensuring that you have the correct one fitted in the first place. Most of these caps are interchangeable and look the same, but, they will operate at different pressures and it is quite easy to use the wrong one,(particularly if the previous owner has fit it and you swap "like for like").
Remember that the cooling system has been designed to function correctly only if the engine manufacturers intended specs. are maintained for the geographical area where the vehicle is supposed to operate.
|
FiF,
You could be right about it helping to cool certain cylinders. Indeed it's a good idea with high power A series engines to 'sleeve' the stat housing to 'control' coolant flow. I would suggest looking toward fan side if the cooling system, is it a electric fan your model?
Steve.
|
|
|
It was the earlier "Bellows" type thermostats that was prone to failure in the closed position. These are rarely used today as an equivalent wax type(more accurate and cheaper) will be available.
>>
Laurie, I'm sorry but I disagree about the failure mode of bellows-type thermostats. I was responsible for re-specifying thermostats during the changeover from 'bellows' to 'waxstat' in the diesel engine manufacturing firm where I worked until a couple of years ago and I will pass on some of what I learned ...
The brass bellows in the thermostat of that type was closed when cold and thus held the valve in the closed position. The bellows expanded under heat and this was helped by a volatile liquid with which it was partially filled. As the bellows expanded, it lifted the valve to the 'open' position. Eventually the bellows would leak/fatigue and fail to return to the closed position, thus it almost always failed OPEN.
The bellows type are NEVER used today, I think they went out in the early to mid 1970s. The main problem with them was the change in their opening rate under different system pressures, and their relatively short life. The replacement wax types overcame those two fundamental problems but they almost always fail 'closed'.
To build on Middleman's point about bleed-holes and jiggle-pins: Thermostats often have a small air-bleed hole which is usually, but not always, fitted with a jiggle-pin. The jiggle-pin is a loose fit and it jiggles (lovely word!) to allow air escape as the system is filled. When the engine is running the jiggle-pin seals off the bleed-hole under the force of the coolant and therefore prevents coolant bypassing the closed thermostat valve.
Onto bypass systems: When the thermostat is closed, the coolant still needs to go around the engine to keep the valves and other parts cool. The normal way of achieving this is to have a thermostat bypass passage which can be blocked by a second valve on the thermostat. This second valve is usually another disc-shaped plate on the bottom of the thermostat but some older designs had a sleeve that rode up and down around the outside of the thermostat and could be prone to sticking. When the main valve is closed to prevent coolant going through the radiator, the second valve opens the way to the bypass passage, and vice versa.
Finally to testing: There should be a temperature stamped on the thermostat, perhaps 88C or 92C, and this is the Start-to-Open temperature. The thermostat can be tested by immersing it in water that is gradually being heated, preferably holding it away from contact with the saucepan or whatever other container is being used. It should start to open at the temperature stamped on it, or certainly within a very few degrees either way. It should then continue towards the fully open position as the water is heated towards boiling point.
The end.
|
Dizzy
I was going to abandon this thread but others kept it going, so here is my two pennies worth.
A long time ago I was involved with a dissertation on engine cooling for a degree.
Here is a synopsis of the findings.
1) Out of 10 different antifreezes tested, all except one increased the boiling point of the coolant.The actual increase is governed by the type or mixture strength.The odd one reduced the boiling point. This one was also inflammable.
2)By introducing a thermostat, whether working or not or open or not, improves the efficiency of the water pump as it acts as a restrictor in the flow, therefore increasing operating pressure.
3)If a hole is drilled into the bellows so that the contents escape,(the actual contents depends upon the maker), to simulate a fault: the stat will open at a higher temp than previous.The temperature can be as much as 20deg higher.
The stat then remains open, with the bellows "strained" to take on a permanent set caused by the excessive high temp.
The driver of the test fleet vehicle was not aware of any defect, except commented on the heater going hot then cold.
When removed the stat was stuck open.
QUESTION: Did the stat fail open or closed?
|
|
|
|
|
|
Thanks Dizzy, most of mine that have failed have been stuck partly open, but I follow your explanation.
|
|
|
|
Fif
I believe you're right! I too seem to recall from many years ago that if an A series engine was run without a thermostat (as some racers were) it was suggested that a blank with a hole about 2cm diameter should be substituted for the thrmostat. Something about a completely open pathway here adversely affecting the coolant flow through the block, which agrees with your thoughts.
That said, I find the fact that several theermostats have failed very odd, and I wouldn't recommend a normal road car be run without one.
Regards
John S
|
Thanks for all your advice folks! I will visit another parts outlet this weekend and try another brand of thermostat, and see how I go!
Incedentally, my 'diagnosis' of jammed thermostat is as follows:
Temperature guage climbs to red fairly rapidly, engine block very hot, thermostat housing very hot, pipe from thermostat housing to radiator still cool, or mildly warm. I did not test any of the thermostats outside of the engine, but replacing them has always rectified the problem (for a while anyway!).
D7
|
Delta, One new thermostat failing would be bad luck
Two would be cause for further investigation.
Three failures.. astronomical odds.
As advised earlier fish them out of the dustbin and test them in a saucepan on the cooker.
Almost certainly they will all be OK.
|
D7,
Like others I think it is highly likely that these 'stats will turn out to be OK if/when tested.
I bet the system is airlocked under the thermostat and then the thermostat can't open because it needs to be immersed in coolant.
The problem is resolved for a short while each time you fit a new stat because you lose the air...but it steadily builds up again.
Possibilities are minor head gasket failure allowing combustion gasses into system or a hose/joint leak that allows air to be drawn back into the system as it cools...had the latter and it can be a devil to track down with no visible leak. It could even be a buildup of air left in the system when you fill it that is then collecting under the thermostat after a little useage.
A pressure test of the system should prove the fault.
MM
|
Furthermore have your 'stats got jiggle pins? Did the oroginal one you took out have one?
A certain tractor I sometimes repair had all sorts of problems due to this air buildup under the 'stat due to being fitted with a cheap 'stat without a jiggle pin.
MM
|
|
MM. In the sixties with the Minor and Mini they used to specify the orientation of the jiggle pin. I think it used to say it should be on the engine block side for some reason.
|
Genuine Frod stats have a little ball bearing that must do the same job as a jiggle pin. The cheap aftermarket ones from motor parts stores do not.
As the geniume ones are only about £9 it is hardly worth buying the cheap rubbish.
|
Keith,
Interesting news about genuine Frod thermostats with ball bearings! :-)
In my rather long missive posted at 21.10, I described the function of the jiggle-pin. What I didn't mention was that, in jiggling, this little item keeps the bleed-hole clean from rust and crud. If the cooling system is absolutely clean and filled with pure water I can see no problem with the ball-bearing idea but I wonder how well it can handle limescale, etc., in an old system on tap water? I am always uneasy about Ford's cost-cutting ideas, having read the book AND seen the film many times over the years!
|
>>I am always uneasy aboutFord's cost-cutting ideas, having read the book AND seen the film many times over the years!
Dizzy that film wouldn't be Die Hard Value Engineering and its follow up Lethal Value Engineering Weapon by any chance.
You know the ones where Bruce Willis and Mel Gibson disguised as Value Engineers go into factories and totally screw manufacturers and the engineering industry in general.
Fif
not all that seriously (it is Friday)
|
Alvin, also some engines have horizontal thermostats and these need the bleed-hole/jiggle-pin to be at the top, for obvious reasons.
Fif, Haynes manuals talk of wax pellet thermostats failing 'open' but I have never come across this myself. You've now made me wonder if 'backstreet' makes can sometimes jam partly open due to poor design and/or manufacture. I feel sure this wouldn't happen with good quality stuff like Wahler.
|
Sorry but I can't let this debate end without mentioning the bypass hose on old minis. Did moggys have them as well?
Steve.
|
|
Yes, Steve, I'm sure all the old 'A' Series had them. I remember buying a hose with convolutions in it so you could longitudinally compress it for fitting without lifting the cylinder head!
|
Dizzy, I seem to remember back in the early eighties all car shops had loads of these things in stock, fastened blister style onto a large piece of card. Thank god for the A+!
Steve.
|
Dizzy, I had a Series11 Morris Minor 1955 803cc and of course like every one else had a Mini.
The Mini had the short solid rubber pipe which by cutting a small amount off could just be fitted with patience, bruised fingers and a bladed tool to slide under it.
However after doing this I don't think anyone would do it again and went for the convoluted pipe you describe.
This job was one of the much discussed quirks of the Mini but I don't think it applied to the Minor or it would have stuck in my mind. However you're usually right so I will have a look in the official Morris Minor works manual next time I'm up in the roof space.
I also recall making a tool in those days to assist in replacing a small plastic seat for the Moulton rubber cone in the rear suspension. It had to be compressed up to get it out. Do you remember that one?.
|
If you have a stat without a jiggle pin and know/think it should have one simply drill a small hole in the stat flange halfway between the edge and middle. Into this fit a small split pin so it's loose and can....err...jiggle.
If the stat sits other than dead level locate the jiggle pin to the highest part of the housing.
As a matter of interest I've just changed the stat on a Mercedes this week and that had a ball type jiggler.
MM
|
alvin
Dizzy is right. All the OHV Minors with the A series engine feature the bypass hose. When I built the engine on mine, I couldn't get the straight hose, but only the convoluted type. I wasn't pleased, especially when I found afterwards that I could have used a section of heater hose, which has the right internal diameter.
Regards
John S
|
|
|
|
|
|
A bit confused here? The coolant system is pressurised. The thermostat only opens the radiator circuit. No thermostat will make the engine overheat more???? Not really, it will confuse the engine sensors going to the ECU , as the engine will not reach operating temperature, the ECU will still think the engine is warm up mode.
|
|
|
|
