Water Pump - Int. vs. Ext. Bypass

[Eric H.]

Technical Advisors - (sorry for the long post)

I am removing the 4461 manifold and Holley 2818 carburator from my '65 small block, which is a (driver)350 CID block with dart iron heads, etc, etc. I've got an Edelbrock Performer ESP manifold going in its place. The antique manifold, carburator and matching 461(?) heads will go into safe storage for a future "matching block" engine project.

I really don't see any reason to maintain the external bypass on the waterpump. I'm going to remove the waterpump and take out the internal bypass plug which I put in place when I installed it. I will then plug the external bypass. This should provide a cleaner and more reliable installation.

The bypass appears to provides a circulation path from the engine back to the waterpump suction. I assume this to protect the pump (maintain some flow through it at all times), since the locations of the two bypasses with regard to the engine coolant flowpath are significantly different.

Also I have noticed that the external bypass is huge compared to the internal one. Was there some kind of restrictor on the original installations?

Anybody see any problems with what I am proposing to do?

Ric

[Duke W.]

Re: Water Pump - Int. vs. Ext. Bypass

Only SHP engines had the external bypass, and I believe it was eliminated in later years. The purpose of bypass circuits is to allow coolant to recirculate through the engine when the thermostat is closed in order to promote quick and even warm-up.

The heater circuit also functions as a bypass, so assuming you have an active heater circuit, you will still have two bypass circuits.

C-48 heater delete was also available on the medium performance engines without the external bypasses, so in those cases, the engines only had the internal bypass, and as you observed, the hole is very small, and there was no restrictor in the external bypass.

As always, it is best to let the engine warm up "at its own pace" by using minimum throttle opening and revs until the engine warms up.

Duke