Disparate engine temps. Water heater impact?

[Streff]

The Port engine coolant temp has always been slow to come up to operating temp relative to the Starboard engine. I changed the sending unit.. still no improvement. I felt that potentially the thermostat is defective and stays open.

As I was working on prepping for winterization for the first time with this boat, I realized that the Seaward water heater has 2 hoses connected to the Port engine.. possibly it has a heat exchanger to heat water from the engine.

Could the fact that the Port engine coolant is routed to heat a 20gallon water heater Be the reason for the much slower climb to operating temp? I cannot determine if the CAT 3208TA has a thermostat controlling the coolant flow to the water heater... which would eliminate my theory if such a thermostat is working.

Any thoughts or comments would be greatly appreciated.

Streff

 

[Flatswing]

Possibly, also common for 1transmission to run 10-20 deg F hotter/cooler which may have an effect until up to operating temp.
I would still check the H/E on the “hotter” side for old bits of impeller/zincs though.

 

[Jeff F]

Is the water in the heater hot or cold on startup? If cold it's a pretty big heat sink getting the tank up to temperature. If hot I don't think it should make a material difference.

 

[Comodave]

I would guess that is why it takes longer to warm up. That is a relatively large water heater so it could take a while. Do they bith come up to temp properly given time? If so I would not be too concerned about it. You could try and have the water in the heater up to temp before starting the engine and see if it comes up to temp faster. It may still take longer because the engine will probably heat the water up some even if it is up to temp with the electric heating element.

 

[catalinajack]

That has been my experience.

The Port engine coolant temp has always been slow to come up to operating temp relative to the Starboard engine. I changed the sending unit.. still no improvement. I felt that potentially the thermostat is defective and stays open.

As I was working on prepping for winterization for the first time with this boat, I realized that the Seaward water heater has 2 hoses connected to the Port engine.. possibly it has a heat exchanger to heat water from the engine.

Could the fact that the Port engine coolant is routed to heat a 20gallon water heater Be the reason for the much slower climb to operating temp? I cannot determine if the CAT 3208TA has a thermostat controlling the coolant flow to the water heater... which would eliminate my theory if such a thermostat is working.

Any thoughts or comments would be greatly appreciated.

Streff

 

[SoWhat]

My port engine with 20 gal water heater takes 1/2 hour to get to typical temp at X rpm, and typical temp is 10-20 cooler than stbd engine. e.g. at 1500 rpm stbd is 180, port is 170. So yes, it's the water heater.

 

[O C Diver]

3208s are pretty big engines. What is your fuel burn when one is lagging the other coming up to temperature? If you're cruising slow burning 2 GPH, then this could absolutely be the case. If you're burning 10 GPH, it's not likely. There is a fairly small heat exchanger in the water heater (as compared to the engine). Also, a 20 gallon water heater is a fairly small mass as compared to the engine mass.

A simple eay to answer the question would be to close the isolation valves for the engine loop to the water heater. Then see it the engines perform the same.

Ted

 

[Streff]

Thank you all for the comments and input. I misspoke, there are 2 connected water heaters so 40gal in total. The Seaward has the HE, the other tank was installed when the Kabola Diesel Heating was installed. Typically the water heaters are cold as the Seaward tank is on leg 2 and the marina has only 30amps and I usually connect to leg 1 for everyday use.

In the spring & summer, We run the diesel heating to heat the water most evenings for dishes and showers. We don’t heat the water the mornings of the days we are underway.

I typically cruise at 7-9 kts between 1200-1600 RPM and it may take the Port engine 25min to reach operating temp. STBD engine gets there in 10min or so.

Thank you all again

Streff

 

[O C Diver]

Streff,

To add a comparison point for you, I have a John Deere 4045TFM75 135 HP and a 20 gallon water heater. I would guess my 4045 is about 1/3 the thermal mass of your 3208. After leaving the slip, running at 2 GPH (40HP) it takes about 5 to 10 minutes for the engine to come up to operating temperature. It takes about an hour for the water heater to reach engine temperature. While the water heater has some impact on my engine, the heat exchanger in the water heater clearly limits the amount of BTUs that can be transferred from the engine.

Ted

 

[Lepke]

Adding valves would allow you to warm the engine first. Valves are also a good idea for any problems in the heater circuit. Instead of shutting down the engine for a leak, you can isolate the heater.
Years ago on a commercial boat, the heater circuit blew a hose. No valves, so I had to rush around to find plugs to close off the heater and restart the engine. And most of my antifreeze was in the bilge.

 

[Jeff F]

Thank you all for the comments and input. I misspoke, there are 2 connected water heaters so 40gal in total. The Seaward has the HE, the other tank was installed when the Kabola Diesel Heating was installed. Typically the water heaters are cold as the Seaward tank is on leg 2 and the marina has only 30amps and I usually connect to leg 1 for everyday use.

In the spring & summer, We run the diesel heating to heat the water most evenings for dishes and showers. We don’t heat the water the mornings of the days we are underway.

Now I'm curious about the purpose of the Seaward tank. Do you ever draw hot water directly from it? Sounds like it may be redundant.

I'm deep into this on my boat right now, hence the curiosity. Installing a diesel heat system and am planning to remove the existing HW tank.

 

[Streff]

Unfortunately, there are no valves to cutoff the HWH from the engine. Based on comments above, I considering either installing valves or simply removing the hoses and somehow plugging the openings on both sides. Sounds like Valves would be the way to go as a flexible option.

Jeff F, The Seaward was the OEM HWH using electricity to heat. We tend to use the diesel WH more often for several reasons. But the Seaward gets used when we are close to another boat on the side of the diesel heater exhaust, when we are connected to 50amp And when we run the generator and want to heat the water.. For e smoke, it gets used when we run the gen when anchoring.