Posted on: February 7, 2016

by Carl Moon in the October 2001 RootesReview:

Alpines do not typically suffer from cooling problems at least to the degree that Tigers do. But, as I have found, it can become problematic even for these small 4 cylinders.

When I rebuilt my 1725 engine I replaced the original water pump with a new aluminum unit (Quinton-Hazell) and this is when the cooling problems began.

I focused on the water pump only after installing a 4-row radiator and a 13″ Flex-Fan, both of which gave only marginal improvements at idle.

Testing the water pump consisted of disconnecting the top radiator hose and attaching an extension that dumped into a bucket. I removed the fan for safety. With the radiator full and a water hose to keep it that way, I ran the engine until the thermostat (160°) opened. I was shocked to see only a trickle of water corning out of the hose at idle. When the engine was revved the floodgates would open! As soon as the engine returned to idle the flow was back to a trickle. I allowed the engine to get over 190° to insure the thermostat was fully open but the flow did not change.

I removed the water pump and compared it to the drawings in the shop manual and later to an original cast iron pump. I found that the original pump impeller was cast iron and had 6 blades. The replacement pump has a plastic impeller with 4 blades. Also, the shop manual specifies a clearance of .040″ from the back of the impeller to the back cover plate. The new one had no clearance and was rubbing the back plate. This clearance spec is probably to maintain a close fit between the impeller blades and pump body. The 4 plastic blades were about .090″ from the pump body!

With a press and hollow spacer I pressed the plastic impeller down until the blades were almost touching the housing. I also plugged the two holes in the impeller. These holes were also on the original but were threaded, apparently for a puller. On the plastic impeller they didn’t seem to serve any purpose.

After re-assembly, I again performed the flow test. The difference was apparent immediately once the thermostat opened. The flow at idle was very substantial, many times more than previous. At high revs there was no noticeable difference than the first test.

I haven’t been able to test the car in very hot weather since the modification but the temperature is much more stable particularly after at highway speed down to an idle.

I have since heard of Alpines that have run hotter after the water pump was replaced. Hopefully this answers some of the questions to this problem. If you have any info on this issue I would be interested in hearing from you.

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