Question - not for the feint-hearted

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How have you tested the Efficiency of your water pump find outlet and check pump is circulating the water well.have you done this??
 
apart from the fact that i have changed the pump twice i can confirm that when i take off the heater matrix inlet hose and turn engine over ( take fuse out to stop her firing) - she pumps into a bag what look like to be very well -

for some reason the temperature (albeit very very hot) of the coolant from the heater matrix and bypass hose will not open the thermostat - it almost as if the pump is drawing water down the by pass hose, through the block, in & out of the matrix and into the expansion tank and also out of the top hose and back through the by pass to complete the circuit - resulting in high/sufficient pressure to blow the expansion tank cap...................... Saying this - dont know why she does not overheat when idling.
 
Are you 100% sure you have all the little pipes on the right stabbings on the thermostat?

With big hose nearest the fan the small pipe pointing to the back is connected to the expansion tank, there is a smaller one pointing almost down that goes to the pump, the next small one pointing to the front goes to the top hose.
 
BenKenobi said:
Are you 100% sure you have all the little pipes on the right stabbings on the thermostat?

With big hose nearest the fan the small pipe pointing to the back is connected to the expansion tank, there is a smaller one pointing almost down that goes to the pump, the next small one pointing to the front goes to the top hose.
Click to expand...

checked this last weekend - def correct trace them back. They are different sizes so pretty dif to get them wrong way round.

Just had a thought - if i restrict the by pass hose slightly then in theory i should get more flow across wax element in thermostat from the heater matrix - this may then open thermostat - in opening it closes off the by pass anyway ?? thoughts.......
 
So looking down from top the little pipes should be pointing toward the outside of the car not toward the engine.

If that's the case it is going straight from top hose back to the pump but if you restrict that too much you could cook something. You should actually have a very good flow across the wax element since it is in the top of the thermostat under all the pipes - there is only one pipe on the bottom - the radiator.

Do you see any water flowing through the radiator bleed into the expansion tank (cap removed) when running and warming up? if you do the pump is working fine.

You are way too far from me to contemplate a cold weekend on a P38 I'm afraid ..
 
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BenKenobi said:
So looking down from top the little pipes should be pointing toward the outside of the car not toward the engine.

If that's the case it is going straight from top hose back to the pump but if you restrict that too much you could cook something. You should actually have a very good flow across the wax element since it is in the top of the thermostat under all the pipes - there is only one pipe on the bottom - the radiator.

Do you see any water flowing through the radiator bleed into the expansion tank (cap removed) when running and warming up? if you do the pump is working fine.

You are way too far from me to contemplate a cold weekend on a P38 I'm afraid ..
Click to expand...


if i am getting good flow across that wax element why then is the thermostat not opening in situ - it opened fine when tested in the kitchen?

yes - looking down onto the thermostat both small pipes are pointing to the outside of the car. the bypass is connected to the more vertical sprout and the return from heater matrix/expansion tank connected to the other.

yes - i get water returning in a steady jet into the expansion tank when lid off
when engine is running and warming up.
 
I think it probably is opening up, problem is finding a way of proving it. The radiator shouldn't really start getting warm since it is bypassed until the stat begins to open.

If it does open and the radiator is getting hot to the touch at top and bottom then you can be reasonably sure that the thermostat is open and the issue is elsewhere i.e. not the thermostat. since you have a stream in the radiator bleed it isn't the pump either, that bleed is proving that you have pressure to the top of the radiator and only the pump can do that, once the stat opens I'd expect that stream to disappear or diminish at least.

It is all a little perplexing why no overheating without the stat - must be frustrating as hell for you. I do have to be honest though and say the only time I have seen this symptom was with a cracked block, didn't manifest until the engine was under load then did so rapidly, would run all day on tickover with no issues. Does it overheat on tickover with the stat in place ?
 
It sounds like the radiator to me. When idling without the fan the radiator gets hot all over, thats because aluminium is a good transmitter of heat. With the fan on the radiator is cold all over except the top tank where the water is going in. Thats because the radiator is blocked therefore easy to cool as not much hot water is flowing through it. If you drive down the road and the car overheats, stop the vehicle get out and feel the radiator all over. If the rad is cold in places but the car is overheating then it can only be blocked circulation, or no circulation A blocked (closed) thermostat falls in the blockage category, but this has been replaced. A faulty water pump (corroded fins or similar) falls in the no circulation category, but this has also been replaced. Short of something alien in one of the pipes, i would most certainly be looking at the radiator.
 
BenKenobi said:
I think it probably is opening up, problem is finding a way of proving it. The radiator shouldn't really start getting warm since it is bypassed until the stat begins to open.

If it does open and the radiator is getting hot to the touch at top and bottom then you can be reasonably sure that the thermostat is open and the issue is elsewhere i.e. not the thermostat. since you have a stream in the radiator bleed it isn't the pump either, that bleed is proving that you have pressure to the top of the radiator and only the pump can do that, once the stat opens I'd expect that stream to disappear or diminish at least.

It is all a little perplexing why no overheating without the stat - must be frustrating as hell for you. I do have to be honest though and say the only time I have seen this symptom was with a cracked block, didn't manifest until the engine was under load then did so rapidly, would run all day on tickover with no issues. Does it overheat on tickover with the stat in place ?
Click to expand...



Frustrating in an under statement - i am thinking along the same lines - cracked block as it has never overheated whilst on tickover with stat in - it is only under load i get the problem.

i dont think the thermosat is opening -its cold underneath whilst being hot on top.
 
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spadgr said:
It sounds like the radiator to me. When idling without the fan the radiator gets hot all over, thats because aluminium is a good transmitter of heat. With the fan on the radiator is cold all over except the top tank where the water is going in. Thats because the radiator is blocked therefore easy to cool as not much hot water is flowing through it. If you drive down the road and the car overheats, stop the vehicle get out and feel the radiator all over. If the rad is cold in places but the car is overheating then it can only be blocked circulation, or no circulation A blocked (closed) thermostat falls in the blockage category, but this has been replaced. A faulty water pump (corroded fins or similar) falls in the no circulation category, but this has also been replaced. Short of something alien in one of the pipes, i would most certainly be looking at the radiator.
Click to expand...

when it overheats the radiator all over is cold apart from the very top. the radiator has been replaced - when there is no thermostat the radiator gets hot ( i mean hot, hot) all over indicating no blockage (i understand what you saying about alluminium
 
For aluminium to be blocked would require serious neglect of the cooling system, 50/50 antifreeze is mandatory not optional in these cars, if that hasn't been neglected and has been changed every couple of years then sludge in the rad is unlikely. Easily proven by back flushing it off the car in any event, I used to half fill and then shake the bejeezus out of them the combination of air and hydraulics shifted no end of crud then back flush hose from bottom to top, rinse and repeat, you could lay it down put some water and rad flush in it and leave overnight. If you can't be bothered radiators aren't particularly expensive but there are three or four types I think.

I'd run the engine hot a few times, then under load as much as possible and then get the coolant tested for 'combustion gases', don't go too mental these aren't an engine that likes to be overheated.
 
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It doesn't require any neglect, only time. Mineral leeching from the block deposits into the radiator core as a white virtually solid deposit which no amount of flushing will remove. It's exacerbated by using tap water.

However I realise I've just put wear on my keyboard for no reason.


Just a random though on the subject because I have seen it once. Have you had the top water elbow off and made sure nobody previous has fitted a thermostat where there shouldn't be one ??
 
BenKenobi said:
For aluminium to be blocked would require serious neglect of the cooling system, 50/50 antifreeze is mandatory not optional in these cars, if that hasn't been neglected and has been changed every couple of years then sludge in the rad is unlikely. Easily proven by back flushing it off the car in any event, I used to half fill and then shake the bejeezus out of them the combination of air and hydraulics shifted no end of crud then back flush hose from bottom to top, rinse and repeat, you could lay it down put some water and rad flush in it and leave overnight. If you can't be bothered radiators aren't particularly expensive but there are three or four types I think.

I'd run the engine hot a few times, then under load as much as possible and then get the coolant tested for 'combustion gases', don't go too mental these aren't an engine that likes to be overheated.
Click to expand...

i wish it was that easy - new rad a few weeks ago. Everything thing in the circuit has been replaced except for the block
 
Wiganerdan said:
It doesn't require any neglect, only time. Mineral leeching from the block deposits into the radiator core as a white virtually solid deposit which no amount of flushing will remove. It's exacerbated by using tap water.

However I realise I've just put wear on my keyboard for no reason.


Just a random though on the subject because I have seen it once. Have you had the top water elbow off and made sure nobody previous has fitted a thermostat where there shouldn't be one ??
Click to expand...

top water elbow - is that the steel tube coming out of the engine where the heater matrix is fed - if yes, then yes its been off - nothing in there.
 
Just had a read through this and although I dont own a P38 just gonna ask a silly question.
You say it overheats is this just the temp gauge saying its getting too hot or is it boiling over.

If its just the gauge then have you checked the temp sensors and gauge?
 
ruffday said:
Just had a read through this and although I dont own a P38 just gonna ask a silly question.
You say it overheats is this just the temp gauge saying its getting too hot or is it boiling over.

If its just the gauge then have you checked the temp sensors and gauge?
Click to expand...

its definitely boiling over and not just the gauge
 
Have you done a cylinder leakage test and checked for bubbles in the cooling system whilst doing it?
Have you defo got the right water pump? I Don't know about these but on Ford Zetecs there are different pumps for different belt setups, two different directions of pump.

Is the steel pipe that runs down the inner wing blocked?
Have you checked every single pipe is connected where and how it should be? not just to the stat?

Have you checked every single pipe stub and connection for blockages?

When you refilled the cooling system did you blow through the rad bleed off pipe?
 
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