View single post by Esprit2
 Posted: 03-31-2015 01:53 am
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Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 321
rday wrote:
Thanks All,
   Your comment on a lighter viscosity oil affecting engine temperature makes me wonder if this is why the engine runs hot.  Around town I have no problems, but any distance under load (up long hills) and on the highway (60 mph +) it does get hot.  I thought maybe that the radiator was partially plugged or it may need a new thermostat.
I was also planning on flushing the cooling system again and replacing the thermostat.  Any other suggestions?
A light oil viscosity might affect engine temperature, but I wouldn't bump it up to the top of the list.

Check the air-fuel ratio. It's reasonable to assume that the carbs might be a little dirty after decades of use and modern alcohol blended fuel. The Federal Stromberg 907 is emissions-lean to begin with, and a dirty jet and/or needle will further restrict the fuel flow, and make a lean condition worse. And lean will run hot.

It's also reasonable to presume the radiator isn't as clean as it once was, and that the thermostat isn't working as it should. The t-stat is easy to change, just select one with a low temp rating (~78 C). The radiator is harder to clean out, but do address it.

The early 907 water pump (all J-H ?) use an impeller with forward curved vanes, small vanes, and not many vanes. It didn't move enough coolant, and was prone to cavitation at higher rpm. Later Lotus 907 water pumps used rearward curved vanes, and more of them. Those impellers are a direct fit into a J-H pump, move more coolant, and never cavitate.

Finally, the 910 Turbo pump uses the best impeller and moves the most coolant. It's impeller's nose is too long to fit in the early 907 pump's housing, but you can have a machine shop shorten it to match the overall length of the early 907 impeller. With that done, re-assemble the pump as usual. The upgraded pump will circulate significantly more coolant, and be a big help with keeping the temps under control. The 910 pump moves the most coolant, and the shortened 910 impeller in the small 907 housing will produce about 90% of the benefit of installing a full 910 pump.

Overheating under load also indicates a possible head gasket problem. Have a hot compression test and a leak down test performed to determine if there's a problem.

Do the compression test with the throttle held wide open, and the engine cranking at 200 rpm minimum (it helps to remove the spark plugs from the cylinders that are not being tested. Jensen-Healey specified a cold test, and pressures of 110-130 psi, cold. Lotus specified a hot test after the engine has been warmed to full operating temperature, and pressures of 150-170 psi hot.