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[robson]

I have had a problem with water level in the expansion tank but cant find any leaks . When running the engine to check for leaks I find that the top hose collapses when the fan kicks in and then goes back to normal when the cooling fan kicks out.Any ideas?

[JamesV6CDX]

I have had a problem with water level in the expansion tank but cant find any leaks . When running the engine to check for leaks I find that the top hose collapses when the fan kicks in and then goes back to normal when the cooling fan kicks out.Any ideas?

What’s the temp gauge doing Ron?

If the hose collapses inwardly but then returns to its normal shape, it implies the hose itself is OK and that a vacuum is causing it to draw itself in.

My first checks would be that the thermostat isn’t sticking shut, and that the water pump hasn’t lost its impeller.

Also worthy of note that if coolant isn’t circulating properly, then it might misreport the actual temperature because water isn’t passing / reaching the probes on the coolant bridge

I’ve responded to your PM, I’m more than happy to take a look

[JamesV6CDX]

Also, the top hose issue can also be caused by a faulty valve on the yellow cap on the expansion tank.

I have a known good spare which I can post to you, to try?

You could also as a little test, run it with the cap off and see if the issue happens (although the water may bubble out when it gets warm).

I don’t suspect head gasket.  That would add pressure and make hoses hard, not cause a collapse. Although - just for belt and braces, can you smell petrol or exhaust fumes in the expansion tank, and does the water bubble inside the tank when started from stone cold with the cap off?

[robson]

Thanks James I have a spare cap if I can find it The one on now was fitted new only a few months ago when I fitted a replacement tank.The temperature gauge  seems ago and the fan kicks in at around 85.Why would the hose regain shape when the fan kicks out.I will find the old cap and report back.

[robson]

Found the old cap will report tomorrow.I assume that the only way to check the water pump is to remove it?

[JamesV6CDX]

Found the old cap will report tomorrow.I assume that the only way to check the water pump is to remove it?

Let us know with the cap.

Been thinking about this more and I think it’s the most likely scenario

As an aside so you have auxiliary coolant pumps on this car? I can’t remember, sorry

[JamesV6CDX]

Why would the hose regain shape when the fan kicks out.

When the fan kicks in, it rapidly lowers the temperature of the coolant. This can cause the pressure in the coolant system to contract and thus the system can drop below atmospheric pressure. If, in these circumstances, the cap is not regulating the pressure correctly, the it will create a vacuum which causes the collapse you are experiencing

Still think it’s the cap on the expansion tank. If it were a collapsed pump, it wouldn’t be likely to show this symptom only with the fans on

[Doctor Gollum]

Found the old cap will report tomorrow.I assume that the only way to check the water pump is to remove it?

Aux belt off and spin the WP pulley. You should hear coolant being moved and feel any binding/roughness/play. Consistent gauge behaviour suggests that the pump is sound.

Incidentally can you recall if the water pump has a metal or plastic impeller?

[JamesV6CDX]

Found the old cap will report tomorrow.I assume that the only way to check the water pump is to remove it?

Aux belt off and spin the WP pulley. You should hear coolant being moved and feel any binding/roughness/play. Consistent gauge behaviour suggests that the pump is sound.

Incidentally can you recall if the water pump has a metal or plastic impeller?

I fitted it about 4 years ago. But I can’t remember for toffee 

[Doctor Gollum]

You have my sympathies, I don't know what day it is...

[robson]

Hello Doc I know the problem and it gets worse

[JamesV6CDX]

Hello Doc I know the problem and it gets worse

Morning Ron, any news? Waiting with bated breath here

[robson]

Update Water level overnight stable. Started engine no smell or bubbles in tank put my old cap on tank. At 90c fan came on and stopped at 89c. The top hose temp was 84c and dropped to 78c infrared  thermometer.The hose pressure dropped but did not show much of a collapse when fan stopped .the tank level was slightly higher than when started. It appears that the change of caps has made some difference to the pressure in the hose. now wait and see how it goes on a run. James I have 2 pumps? one under the battery and one under the expansion tank.

[Doctor Gollum]

A new cap then and it might be prudent to replace the top hose as well... If it is getting really soft, then it's days are done.

[JamesV6CDX]

Update Water level overnight stable. Started engine no smell or bubbles in tank put my old cap on tank. At 90c fan came on and stopped at 89c. The top hose temp was 84c and dropped to 78c infrared  thermometer.The hose pressure dropped but did not show much of a collapse when fan stopped .the tank level was slightly higher than when started. It appears that the change of caps has made some difference to the pressure in the hose. now wait and see how it goes on a run. James I have 2 pumps? one under the battery and one under the expansion tank.

It sounds to me like the tank cap was the culprit, if, having changed it, the hose has stopped collapsing. The slight drop in pressure you see is totally normal. If it’s not collapsing anymore, I think that’s a win

It’s totally normal for the water level to rise in the expansion tank when the engine is hot. The “max” line is for when the engine is cold. It will go above this when hot (especially if the cap is loosened)

Let the car fully cool. Make sure the water level is on the right line. Fit the cap tightly and go for a drive / see what happens. I think you’re sorted.

I agree with DG, if the hose has taken a beating, replacement won’t hurt at all