I have a alpha style mercruiser outdrive being powered by a 351W. Ever since I bought the boat, it has always run hotter than I thought it should (180F~200F). I spoke with the previous owner and he confirmed that it always ran hot for him as well at times.
I have replaced the water pump impellor several times as well as the exhaust manifolds and risers once each recently with new parts. I know that the circulating pump is pumping lots of water at all RPM's.
The way that my cooling is set up (as specified in the Mercuiser manual) is:
1. Water is pumped from outdrive to thermostat housing at front of engine.
2. Some of water is taken from housing to circulating pump and circulated through the engine where it comes out of the intake manifold and back into the thermostat housing.
3. Some of water is taken from housing, circulated through the exhaust manifold, and sent back to the thermostat housing.
4. There is a bypass next to the thermostat that allows some water to flow to the exhaust risers. The thermostat only throttles the second opening for water to get to the risers.
My question is: should I reroute the cooling lines so that the water comes into the housing, circulated through the engine, passes through the exhaust, and then injected into the exhaust riser to be dumped overboard in the exhaust? This will help reduce the temperature of the water being circulated through the block as it won't go through the manifolds first?
Schiada.... The raw water pump is in the sterndrive and not driven by a belt.
Boatbroke, those systems always ran warm because of the water returning from the manifolds. Make sure it has a Mercruiser 140 thermostat, not an automotive one.
The best, and most expensive, way to solve the problem is to replace the thermostat housing and exhaust manifolds with a late model setup. If you plan on keeping the boat this is the best option.
Thanks for the replies. I was sure someone would come along eventually with some experiences like this.
I tried running a 140* thermostat last weekend and that's when it got hot fast. Up until then, I have always ran without a thermostat with the temp gauge hovering at the 180* mark. I don't have a way to validate that the gauge is reading correctly other than to hold my hand on the riser and compare how long it takes before I have to pull my hand off agains other boats.
BDMarine, can you give an example of what constitutes a late model setup? I've looked at various systems (so many that I don't remember most of them) and it doesn't look like any of them are that much different. Do some have less resistance than others to water flow?
I have a feeling that you're talking about stainless exhaust. Is that right?
I screwed up!!! Sorry!!! I knew you were talking about the ford and completely forgot with my recommendation, thinking Chevy.
I was referring to late model Mercruiser manifolds, elbows, thermostat housing, and hoses.
I think re-routing the hoses so they dont bring water back to the thermostat housing is probably the best idea. You just have to take a close look at the way the thermostat housing distributes the water and make sure it makes sense.