Correct Thermostat for fresh water cooled A4

[Drexell]

Can you point me to the correct thermostat for a fresh water cooled A4? I'm having some overheating issues. My first step is checking the thermostat and perhaps a flush (or replacement) of the heat exchanger. I've read that the freshwater system uses a higher temp thermostat to keep the operating temp around 180 degrees. The system uses the rear pump for the freshwater side and a flywheel mounted pump for the raw water intake.

[Don Moyer]

Drexell,

We recommend the standard 140 degree thermostat (OEM or aftermarket). In fresh water cooled engines, these thermostats will maintain a temperature at cruising RPM in the range of 160 to 185 degrees in most of our operating areas, due simply to the capacity of all heat exchangers commonly used on the Atomic 4.

We removed the 180 degree OEM thermostat from our online catalog quite some years ago because it frequently allowed temperature excursions into the 200 degree range and above. This was as much due to the design of the bypass type of cooling systems used in late model engines.

Don

[Drexell]

Don,

Thanks for the info about thermostats. You mentioned the bypass on late model engines. When I took delivery of the boat ('76 Ranger 33) last fall, I noticed there was a clamp on the bypass hose just before it entered the thermostat housing. Is this acceptable or is it a way of compensating for an inefficient heat exchanger or blocked coolant passage?

Drexell

[Don Moyer]

Drexell,

There's nothing particularly improper about putting a bit of restriction on the bypass hose. Universal recommended the practice in the late 1970's. Having said all that, I usually consider a hose clamp to be more or less a temporary fix until something more permanent can be done. Many people prefer to install a small ball valve in the bypass loop so that they can manually control the amount of bypassing water.

Don