90 hp L drive water recirculation- cooling system

[steveinelpaso]

Hi all, I have a 1990 90 hp Force L drive, which for this last summer (since I bought it) has been pretty good. I take it in the Potomac up by the monuments. A few weeks ago, I went under a bridge under construction, was out of the channel, tide was out and got stuck in the mud. Cleaned out the impeller, also a water hose was clogged. Checked the thermostat only to find there was not one, ordered the parts and am ready to install. My question is, the impeller is on the lower gear casing, and the thermostat is on the top of the engine. In a car, the water pump recirculates coolant until it heats up, then the thermostat opens and coolant from the radiator can enter the engine. But how does water on a Force engine recirculate before the thermostat opens up? It does not really affect the repairs I am making, but it is a mystery to me.

 

[WillyBWright]

Re: 90 hp L drive water recirculation- cooling system

It doesn't recirculate. It pumps in and dumps out. The thermostat holds water in the block til it warms up at low RPMs, but is always dumping out through the exhaust. Above half throttle or so a bypass valve allows water to pass straight through everything and the thermostat is bypassed.

 

[steveinelpaso]

Re: 90 hp L drive water recirculation- cooling system

OK, thanks, that makes sense. I did not know about the bypass also. Without the thermostat, the boat always ran rough at low speeds, I think because it was too cold. I backflushed the system yesterday, installing the stat cover without the thermostat, and you should have seen all the mud that came out from the intake tube (which I disconnected from the lower gear assembly). Got it all back together, ran it with muffs, and it seems to be fine now. Thanks