SBC V8 Water Pump Failure, 3 Styles of Pumps Tested BYPASS THERMOSTAT UPDATE Options

[nick mironov]

My Renegade water pump failed yesterday. The pump impeller is stamped steel and the blades all just folded over or sheared off. I understand that the cast impellers are much stronger, but that not all manufacturer's cast models will fit into the Renegade housing. Anybody have experience with cast impeller pumps that will fit into the Renegade housing?

Since there is no bypass in the Renegade system, Renegade instructions are to limit the motor RPM to 3,000, or less, untill the thermostat opens. I have observed this, but the pump still failed after 5,500 miles. Renegade now makes a bypass kit, which I going to try, but I would still like to get a more durable pump.

Nick

[LvSteveH]

This is Scott using Steve's 914 World account for now...

First of all...I have seen the failures that are discussed in this thread. There are several reasons why the failures have increased over the years including lower quality parts used to build the impellers, higher RPM's due to better aftermarket engine technology, cheaper thermostats that don't flow enough volume when open, more debris and blockages in the ageing engine blocks, and just the fact that there are so many SBC 914's and 911's that have finally found the road...and not just a dark corner of the garage covered in dirty laundry and kids toys!

My little orange 914 from years back that some of you named "Peal", went through a few water pumps in it's day. I was stranded on a cold windy night on the long State Line grade with just such a failure...so I completely understand the frustration. BUT...it was the cast impeller/water pump that failed that time at the shaft seals and not the typical carnage with the impeller failures. That engine was frequently spun to 6800 RPM and was never driven easily I can assure you.

Where we saw the most consistent failures was with customers that revved the engine past about 2500 or 3000 RPM before the thermostat was open. Drilling two or three small holes in the T-stat was the easy way to relieve the pressure a little so the water pump would have a fighting chance. Often the pump would sustain damage after just such a high RPM rap of the throttle when cold, but it would still move some water. BUT, just like the paper clip, eventually the blades would give up and curl themselves around the shaft.

In an attempt to help our little water pumps to live longer, we developed an easy fix with a bi-pass T-stat design. Water temps have been consistent, water pump failures seem to be less, hose pressures have been more stable, no need to drill holes in the T-stat, heater core temps have increased on cold days, and it's easy to install.

In summary, keeping the RPM's down when your engine is cold, is a good idea in general and may help your water pump last. Installing the cast water pump was a solution I have tried, but they are not completely immune from failure. Different impeller designs will change flow rates that will effect your ability to cool. Using a good quality, high flow T-stat, with two or three small holes drilled, will work very well for this application. Flushing your block and cooling system completely will also increase flow and thermal transfer allowing the engine to cool more efficiently. Installing the new bi-pass system seems to be the next logical step if you are still having issues.

On our end, we have looked into impeller suppliers and we think we are using the lesser of all the evils. There is some really bad junk being made out there, but the ones we have are lasting when reasonable care is exercised.

If you have any further questions, you are welcome to call Steve or myself here at the shop. Thanks for all the good input here on 914 World without the drama that finds it's way into these boards from time to time. Keep up the good work!

Sincerely,
Scott >>> Renegade Hybrids
www.renegadehybrids.com
(866) 498-2421 toll free