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Engine preheat of winterized U320 coach that has Aqua Hot

November 16, 2020, 08:22:03 am

I have winterized my 2004 U320, including running RV antifeeze into the hot water lines of the Aqua Hot. My question is, Can I run the engine pre-heat if  I need to start the coach in cold weather? Coach is plugged into 50 amp. Does engine preheat require Aqua Hot to run, or is it done electrically?
Thank you

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Re: Engine preheat of winterized U320 coach that has Aqua Hot

Reply #1 – November 16, 2020, 08:27:04 am

As I understand it the preheat is a loop from the aquahot to the engine, the same loop that allows engine heat to heat the aquahot while driving. It should not affect the domestic water.  Either the diesel or electric needs to be on to heat the engine.

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Re: Engine preheat of winterized U320 coach that has Aqua Hot

Reply #2 – November 16, 2020, 08:39:40 am

As Forest said, turn on the diesel burner.  It will bring the Aqua Hot coolant up to temp in about 15 minutes.  Interior heating is now available.

Then turn on engine preheat for one to two hours and you engine will fire in frigid conditions.

The electric element does not have the capacity to do this in frigid conditions.  You can turn it on too to help out which would be fine.

And, your fresh water system is still winterized.

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Re: Engine preheat of winterized U320 coach that has Aqua Hot

Reply #3 – November 16, 2020, 10:06:51 am

I use this feature frequently.  If it is cold outside adding heat to the engine will help it start easier.  If it is down to about 30°, two or three hours in the morning is usually enough.  Run the diesel heater, electric won't keep up.  Much colder than that I will turn on the diesel burner and leave it on over night with the engine preheat on.  Coach heat on too.  In the morning at zero degrees outside, starting the engine is easy and it will show coolant temps at 70° right away, just like a summer day. 

If you are driving in cold weather leave the diesel burner on and set the coach LR thermostat to 75 to keep the LR heat on. Warm air from the dash heat or defrost will fool the thermostat and LR heat will not do much.  BR can be on too if you want but set to a lower temp.

The engine will heat the AH while driving. We see about 140-150°.  That is often enough on its own for some heating if it is not too cold.

Everyone has a different comfort set point.  At perfectly comfortable temperatures for us our Houston friends are freezing.

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