Triumph Repair: TR7 Water Pump, pump impellers, rough surface

Question
Hi Howard:

Thanks for answering my question about the noise in the front end of my '79 TR7.  I will be working to diagnose that very soon.

In the recent past, I replaced the water pump on this car.  In addition to replacing the water pump, I also replaced the shaft bushing.  Since this time I have not run the car very much, maybe putting 150 miles on the car.  I noticed yesterday that I'm getting coolant weeping from engine block slot below the water pump.

Should I be concerned about this right now?  Do you think the seals have yet to "bed in" yet.  When the car runs it does not weep.  It only seems to leak while it is not running (strange).

Any advice would be appreciated.

Thanks
Matt

Answer
Hi Matt,

That slot in the block is to allow coolant that gets past the water pump seal to exit the block and not get into the oil in the pan. (providing the oil seal is good)

You definately have a problem that must be attented to. If it only leaks with the engine off just after the car has run then you first need to test the pressure cap to see that it is not a high pressure cap. You need a low pressure cap of 7 PSI to 14 PSI any cap higher can cause the problem you have.

Try this, Since you say that it does not leak when running, then as soon as you stop release the pressure by loosening the cap and leave it loose. (be careful not to get burned by using gloves or a large rag)

This will release any pressure on the system. Keep in mind that every engine's cooling system raises in temperature and pressure as soon as you shut an engine off. This increase temperature and resulting pressure is blowing past the seal. The seal face may not have seated well when you installed the new pump and I have seen many pump impellers with a rough surface on the bottom where it mates to the seal of the pump body and thus it does not seal well. On some I had to polish that surface as a rough surface will soon eat the seal face and cause a leak.

The reason the coolant raises in temperature when an engine is shut down is because the amount of heat transfer from the engine (mainly the head) to the coolant is not as good when the coolant is moving fast over the metal and when the engine stops, the coolant then gets good heat transfer and it raises the coolant temperature and that raises the pressure. Many car manufactures design electric fans so that they continue to run even when the engine is shut down so as to cool the radiator which does transfer the heat out of the coolant enough not to cause this high temp and pressure build up.

let me know the result of the cap release and what pressure cap was on it.

Howard