Water pump failure ?

[Polse7317]

I have a over heating engine and overflowing coolant after +- 20 minutes running . My radiator is new as all the hoses, tested 2 new thermostats . The coolant level has been checked ( +- 1 cm above the coolant tank floor)
. the only part i have not replaced is the water pump. When i inspect the impeller , i see a space beetween the impeller and the casing of about 2 mm, this space disapears when i press the impeller against the casing . I haver ordered a new one and the space is about 0.6 mm. I wonder if that abnormal space can explain an insuficient flow and my overheating problem ?

anyway i have ordered a impeller kit before put in a new pump and i'll set the impeller with a space of 0.6 mm . I prefer to keep my ""old" pump , if the problem is what i suspect....?

[mgcjag]

Hi Yves...i think yes if the impeller gap is too large you will get reduced flow and possibly no flow..there is obviously something wrong as you say if you press the impeller the gap closes...this should not happen..... Steve
This may also help viewtopic.php?f=3&t=10145&p=80616&hilit ... ing#p80616

[jagwit]

I have a over heating engine and overflowing coolant after +- 20 minutes running .

IMHO, there could also be other reasons for your problem worth investigating:
1) Is your car fitted with the CORRECT thermostat? I'm not referring to its temperature rating, I'm referring to its physical format. Does it have the sleeve that closes off the bypass port? (Its that long vertical slot behind the thermostat). For the '65 I worked on it was C3731. This bypass circuit is intentional and is meant to allow fast warm-up of the engine, but when the thermostat opens, it should close this bypasss circuit off, forcing all coolant through the radiator, unless you also have the next problem:
2) How much coolant can escape from the pipe inside the header tank via the hole for the otter switch and flow UNCOOLED via the "filler pipe" on RH side of the header tank to the COLD side of the radiator, thus creating a second UNINTENDED bypass circuit. On the '65 I worked on, this second bypass route also allowed a significant amount of coolant to bypass the radiator. I installed a "plug" in this hose with just a tiny hole in the top to allow air to escape back to the header tank -but blocking any significant coolant flow. In my case the "otter switch hole" was so large, this very hole is now also used for filling the cooling system.

[Polse7317]

I have put a new impeller and bearing in the pump casing with the great help of a friend mechanic .( thank's for the press )
I'll test the pump tomorow :

[Doug Buchan]

Hello,

Is the timing cover original to your engine?
The reason I ask is that there have been instances where it's been changed to the later 3" involute variant whilst retaining the earlier 2-3/4" impeller pump.
The result is lack of flow due to cavitation.

[Polse7317]

Hi Doug , i don't know if it is original.... I think so but not sure. I have fitted the original pump with the new impeller , and tested the temp in the garage.... i have no more coolant over flowing after 1h 30 m idling ( i am already glad with that ! ) but the temp is about 90 C° on the dash gauge , and it goes to 100 C° when the engine turns at +- 1500 rpm , so i am still worried .... i have tested with and without by-pass and it is the same. May be the gauge is not accurate as the fuel gauge ?

[ralphr1780]

Yves, good that you no more have overflow as this is already an improvement. However, you should check the temperatures with an IR gun and not rely on the gauge readings if this has not been duly verified before. A modest investment anyway for a tool to have in your garage. The gauge or sender (or both) could be giving deviating readings.

[Polse7317]

Hi Ralph i have tested the temp as you say with a temp gun:

I have noticed when the engine is running since 30 min: 70 C° at the headertank enter , +- 75C° between the tank and the radiator , 56C at the top radiator entry

[Polse7317]

To answer to Philip, i have fitted a sleeved thermostat and tested it , no difference ....... ! but i don't understand about the pipe in the header tank you talk about? my header tank has inside only a "floor" which separate the bottom and the upper of the tank . ( 1 floor and " basement" on the pic above

[jagwit]

My apologies Yves

It seems my comments do not apply to your car. Your header tank does not have the 3rd "filler" pipe, the later models have, so you won't have the 2nd unintentional bypass route.

Your IR readings look perfect to me.

This would suggest that your temp gauge is driving false readings. Have you checked the voltage "stabiliser". It caused UNDER reading in my case, but it can just as easily cause over reading.

[Polse7317]

The voltage regulator has just been replaced... i don't know if i can modify the gauge level ?

[jagwit]

It CAN be adjusted. There are several threads on doing this.