ROVER P6 NOISY COOLING SYSTEM
Q
I have an annoying problem with my 1976 Rover 3500S which I am hoping you can help me with. Generally, the engine runs really well and is fine on short journeys. If I take the car for a run that is longer than around 30 minutes, when I stop, I can hear the coolant bubbling and I can see steam coming from the expansion tank overflow pipe.
I can see no obvious leaks in the cooling system and the temperature gauge is reading normal. I do have to top up the coolant at regular intervals, but this is not a great amount. I have checked the timing and mixture and I have carried out a compression test which suggests that all cylinders are equal and would hopefully dispel the possibility of a head gasket failure. The colour of the spark plugs also suggests an even burn of the mixture.
AThe first possibility is that the radiator’s pressure cap has failed and is not retaining a suitable pressure in the system. This would be the first point to check. Providing this is OK and as you do not report a high pressure build up in the cooling system, then I would assume that the head gasket has not failed – it is likely that this would reveal itself after a shorter journey than 30 minutes.
I would though doubt the accuracy of the temperature gauge, and would suggest that perhaps the gauge is reading slightly low and that the problem is due to either a partially blocked cooling system or the thermostat which is not functioning fully. With this in mind I would check the thermostat, and at the same time take the opportunity to flush out the cooling system. I would add a word of caution though, as flushing the cooling system on a vehicle of this age may well highlight a few weak spots in the system that have previously gone unnoticed. It is also possible that at some point in the past an additive has been used to block up a minor leak, and this additive may be having an adverse effect on the system if it is blocking narrow passageways.