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Old 12-19-2014, 02:00 PM   #1
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Tiffin Owners Club
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Engine System Preheating

I think this is a Tiffin-specific question. I have at least two engine preheating systems, and maybe a third. The first picture shows a switch marked "Engine Preheat". I assume this is some sort of 12 volt device because all the rest of the stuff on that panel is 12 volt. I'm thinking it could be glow plugs if they aren't cycled during the "wait to start" interval. When I picked up my coach from Cat after its yearly PM, this switch was on.

The other system (and maybe a third) works on AC from plug(s) in the power bay. I think that the yellow plug is some sort of block heater or crankcase oil heater, but I'm not sure. This plug looks like it goes to the junction box nearby. The other plug's cord disappears into the interior. I'm wondering if this could be a fuel heater or some other sort of winterizing system (the original owner lives in Vermont).

Both plugs were disconnected when the coach was delivered to me, and I haven't plugged them in. However it is getting colder in Tidewater, so I'm sure I will soon need some extra help getting the Cat started.

Can anyone confirm what these devices do? As always, thanks for sharing your experience.
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Old 12-19-2014, 02:11 PM   #2
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One of the plugs appears to be for the engine oil heater, which is turned on with the switch you pictured....the other plug I would venture a guess to be a trickle charger for your chassis batteries.......at least that's what my set up is

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Old 12-29-2014, 09:12 PM   #3
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Smile engine preheat

I did call Tiffin about the engine preheat switch on my 2007 phaeton with a cat.

They told me that it in deed was the engine block heater and only worked on 120 volt when plugged in or when the gen was running.

Don't know for sure about the other plug in that bay. If you find out for sure let me know or post it.

Stan in Tn.
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Old 12-30-2014, 11:56 AM   #4
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I agree with Gary. My bet is that one would be preheat (the large yellow plug), and the other is probably to a battery tender. One thing you do want to do is plug a house lamp into the two different receptacles to find out which one is controlled by the preheat switch. If you don't, either your engine preheat will always be turned on, or your battery tender will only work when the engine preheat is turned on. The "Battery Minder" battery tenders have been known to drain chassis batteries when they are connected to the batteries but not AC powered. So if the battery tender is plugged into the same receptacle that is controlled by the engine preheat switch, you will risk draining your chassis batteries every time your engine preheat is turned off.
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Old 12-30-2014, 12:22 PM   #5
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The center 120 volt box with only a single outlet is probably always live when plugged into shore power or operating on generator. The box on the right with the barcode is the 12 volt relay that switches the engine heater (120 volt) on or off based on the position of the 12 volt pre-heat switch on the dashboard. Usually the pre-heat plug is labeled (seems to be a tag on the wire leading to the yellow plug). I don't know what the other plug next to the yellow plug is but it is not the Battery Tender which is a black cube with two lights and is usually plugged directly into a 120 volt outlet. You only have a single engine block heater. Hope this helps.
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Old 12-30-2014, 02:51 PM   #6
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It can vary depending on what day your coach was built, but from what I can see, the flat cord goes to the block heater. The yellow plug supplies power to the block heater relay which is in the square metal box with the outlet.

The yellow plug is connected correctly. The flat cord needs to be in the outlet on the relay box. Otherwise, you will be supplying power to your block heater any time that AC power is connected (cord or generator).

FWIW, some coaches also have the water heater connected the same way as the block heater. That relay and associated outlets may be in the same bay or they may be in the water heater compartment. (see my first sentence)

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