Installing block heaters and thermostats 8v71

[davidwigler]

Hello everyone. I'm finally getting ready to drain the cooling system, replace hoses, and install new mechanical temp gauges and Hot-start block heaters and thermostats. A few questions:

1. I have located the 1" plug on the port side of the front of each engine where the heaters are supposed to be inserted, but it seems pretty high on the block which would be inefficient in circulating the warm coolant. There are 1" plugs on the sides of the blocks down low, but I can't tell from the manual if these are in the coolant or oil chambers of the block. I suppose it wouldn't hurt to open one. Any experience with these plugs?

2. Where in the block do you install the Hot-start thermostats? Does it matter?

3. The thermostats are 100-120 degrees, which seems wasteful to leave it on that high all the time. I was thinking about using low voltage thermostats and relays in the engine rooms to cut the power off at, say, 60 degrees room temperature. Any ideas?

4. I have 120 volt outlets in the engine rooms, but for a dedicated wiring source I'm thinking a single 10/3 wire to a new 20 amp 120 volt breaker on the panel should be sufficient for both 1,000 watt heaters. I want to be able to shut the power off at the lower helm before starting the engines. I'll add a warning label below the start buttons. Any comments?

[GJH]

Here is where the thermostats on my 8v92's are FWIW:



I believe the PO had it tapped, being no existing opening there. You could consult your heater manufacturer for advise.

I suppose if your purpose is merely to winterize your boat (that is, it won't be used during "block heater season") in lieu of a tapped in thermostat, you could use an external one like for electric baseboard heaters or in greenhouses, with the aim of keeping the ER temperature to a certain minimum. I like having the 100 degree cut-in because 1) it gives us quick smokeless starts and 2) by opening the engine room doors it provides dry radiant heat for the lower level of the boat, and 3) keeps the ERs dry.

Winter before last we had the boat out of the water for three months, some due to repairs and the rest because the weather was so lousy. Having the block heaters on really was nice then as well. We only needed one little ceramic heater in the forward section to help some somewhat exposed water lines. When it came time to go back in the water everything was dry and the engines started right up clean as could be.

I like your idea of hard-wiring them to a breaker below and a switch up top.

[captddis]

Hello everyone. I'm finally getting ready to drain the cooling system, replace hoses, and install new mechanical temp gauges and Hot-start block heaters and thermostats. A few questions:

1. I have located the 1" plug on the port side of the front of each engine where the heaters are supposed to be inserted, but it seems pretty high on the block which would be inefficient in circulating the warm coolant. There are 1" plugs on the sides of the blocks down low, but I can't tell from the manual if these are in the coolant or oil chambers of the block. I suppose it wouldn't hurt to open one. Any experience with these plugs?

2. Where in the block do you install the Hot-start thermostats? Does it matter?

3. The thermostats are 100-120 degrees, which seems wasteful to leave it on that high all the time. I was thinking about using low voltage thermostats and relays in the engine rooms to cut the power off at, say, 60 degrees room temperature. Any ideas?

4. I have 120 volt outlets in the engine rooms, but for a dedicated wiring source I'm thinking a single 10/3 wire to a new 20 amp 120 volt breaker on the panel should be sufficient for both 1,000 watt heaters. I want to be able to shut the power off at the lower helm before starting the engines. I'll add a warning label below the start buttons. Any comments?

I have two brand new Ranco adjustable thermostats for the block heaters. PM me if interested.

[JLR]

The setup I have seems to work well. I have the block heaters hard wired to an adjustable thermostat in the ER. That is controlled by a switch I have in the pilothouse which gives me the option of having the block heaters off, on (overriding the thermostat) or on the adjustable thermostat. That way, I can leave them on the thermostat during the season, or, if I want to make sure that the engines are fully warmed before starting, on overnight, and off during cruising.

[Canuck Dennis]

On my 12 71's the heaters are installed port side tapping below the exhaust manifold, I keep them about 100f all year, summer and winter...our electric here is flat rate so it keeps everything toasty, specially today, was 32 f last night.

[rsmith]

I know people on here seem to love these heaters but I have to wonder about the long term effects of keeping them on all the time. Years ago I had a engine preheat system put on my Cessna 340 aircraft. Aircraft engines need to be preheated below 20*F. After about a week I started noticing condensation around the oil fill cap. After talking to the MFG of the system we determined that as the air in the engine is heated it rises and condenses in the top of the engine where it starts to cool. The answer was to plug the exhaust from letting cold damp air in and to leave the oil fill caps loose to vent any moisture, I also covered the engines with blankets to keep the heat uniform. When I had the engines overhauled I asked the engine shop what their thoughts were. They said they saw pitting and spalling in the top ends of engines that had these systems installed.
I have to wonder if the same senario is happening in these marine engines using heaters. Cold moist and salty air can definitley be drawn thru the exhaust. I would worry about running the heaters at too low a temp that would be below dew point and cause condensation in the engine. Dew point can be at any temp. We used to design waste heat recovery boilers and if the outlet temp fell below 900*F we had major corrosion problems.

[GJH]

Given the configuration of the exhaust on my boat, given the laws of thermodynamics, it is difficult for cold moist air to travel up and in to a heated block. With no heaters, everything will equalize, and the chances for moisture intrusion are good. I'd agree that not heating them up enough could be an issue, which is why the heater manufacturers recommend and build the thermostats they do and the wattages for a given engine. It looks like they either just want to keep the thing above freezing with a 40 degree cut in option, or keep it hot with the 100 degree jobs. These things see most of their application for land based engines exposed to extremely cold temps.

Maybe Sky could educate us a bit on that, being a heavy equipment type guy from the frozen north.

[SKYCHENEY]

Sorry George. I don't know if I can be of much help regarding condensation. We use heaters in the winter just to aid in starting. We usually don't plug them in until it gets below freezing. Most everything that gets plugged in is used everyday anyway, so moisture is probably not much of an issue.

[Canuck Dennis]

On my 12's the exhausts are water lift type, the mufflers being in the engine room, the exhaust hose's are more than 25 ft long within the boat, the rest of the boat and the e/r is maintained over 65 f in the winter so I see little chance of condensation in the mains, (hopefully of course)

[davidwigler]

I don't see how cold air traveling through the exhaust could ever cause condensation in a warm engine block. My understanding is that condensation occurs as warmer air cools down to the dew point, because warm air holds much more water vapor by volume than cold air does. That is why condensation usually occurs on surfaces that are colder than the air (i.e. exterior windows and the shower door).

That does explain somewhat the benefit of the 100-120 degree thermostats. At a steady warm temperature there will never be any condensation in the engines. If the engines cycle back and forth between 65 degrees on warm afternoons and 40 degrees at night, there might be an endless cycle of evaporation and condensation in the block.

Thanks for all of your helpful comments. I'm ready to buy a 1/2" breaker bar and get to work.