High Temperature With New Thermostat

[whalechaser]

Hi,

I have a late model raw water cooled A4 in my Bristol 32. I've just replaced the water jacket plate, completed an acid wash, and put in a MMI late model thermostat. Prior to putting in the thermostat, after the acid wash, I ran the engine for several hours to flush the system. The engine never got much beyond 110 degrees or so. Now, with the new thermostat installed, the engine is wavering between 180 - 200 degrees. Before the work the engine was plumbed with a bypass valve for the hot water tank heat exchanger, which I adjusted to keep the engine at ~ 140 - 160. At the moment I'm just running it with "normal" plumbing, with the hose from the T fitting directly into the thermostat housing.

I would have thought because the engine ran cool without the thermostat the water flow was pretty decent, but maybe there is some blockage? Ideas?

Thanks,

Chris

[Dave Neptune]

If you have no t'stat you must use the "bypass valve" otherwise the water just goes around the engine and not through it.

Dave Neptune

[Dave Neptune]

And

Chris a standard automotive t'stat will not work unless you have the proper adaptations.

Dave Neptune

[whalechaser]

Dave,

Thank you for your reply. The thermostat I have installed is not a standard automotive model - it is the MMI three spring double acting model sold by Moyer. Previously I had installed the other late model thermostat sold by moyer and all was well. Also, when I initially ran the motor after the acid flush I had pinched the bypass hose between the t-fitting and the thermostat housing to ensure water flowed through the block and it was still running cool. I suppose my next step is to take the exhaust pipe off the manifold to see if there is crystalized salt in there restricting water flow and to re-plump everything with the ball valve as was done previously.

Thanks again,

Chris

[JOHN COOKSON]

Maybe I'm not understanding this situation correctly......but anyway:
The engine ran cool without a thermostat.
After a thermostat was installed the engine ran hot.
SO: There is something going on with the thermostat or the installation - probably the thermostat in not opening or not opening all the way.

If there is reduced water flow through the (entire) cooling system it would indicate a blockage or a water pump issue is causing the overheating.
If there is a normal flow of water through the (RWC) cooling system and the engine is running hot it means there is not enough water going through the engine; rather the water is going around the engine VIA the bypass.

TRUE GRIT

[sdemore]

Check the tube inside the thermostat housing. When the thermostat is closed, bypass water flows through a tube in the housing. As the thermostat opens, the water flows through the engine and the bypass water is blocked by the opening thermostat. That bypass tube corrodes quickly and when it does, the thermostat can't block it off. When this happens, too much coolant flows through the bypass instead of through the engine, and it runs too hot. That is why pinching the rubber part of the bypass will make it run cooler, but not pinching it makes the engine run hotter.