White Smoke/Steam

[Unregistered]

My late model raw water cooled A4 started to overheat this summer. I reviewed the literature on line and in your manual and determined it to be the thermostat. I replaced the thermostat and it corrected the temperature to 180 degrees.

Subsequently, a week later my boat was moored in some bad weeds and again overheated. I had limited water flow from the exhaust.

I removed the weeds from the water intake and inline strainer and I replaced the impeller in the water pump. Suprisingly, this did not correct the lack of water flow and overheating. After much discussion, I replaced the original 30 year old water pump with your new MMI 502 pump.

There was immediate improvement in the water flow and the temperature stabilized at 180 degrees, but there was still all kinds of white smoke. I again reviewed the manual and installed a spring loaded 1.5 psi check valve in the bypass loop.

The engine is now running at 160-165 degrees the correct temperature, but there is still lots of white smoke.

Is this white smoke a result of some type of restriction in the exhaust manifold? I am running out of ideas.

Thanks,

Bruce

[Don Moyer]

Bruce,

I can't quite determine from your report what the current situation is with respect to the total water flow out the back of your boat.

Your new thermostat (aided by the resistance of the check valve) is apparently reducing your bypass flow sufficiently to maintain a normal temperature within the engine, but if there is a significant restriction in the "T" fitting, you could be losing enough of your total flow (even with your new pump) to the point that there's not enough water flow remaining to cool the hot section of your exhaust.

If you haven't had your side plate off to clean in recent years, you could remove the "T" fitting and clean out what ever restriction is in the diverter cap inside the plate, and then reinstall the "T". This should give you relief now, and you can remove the plate later as a winter project.

Don