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  #1  
Old 10-20-2008, 12:30 PM
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Fuel tank heater pad- how hot is too hot?

Greets, I bought a 500 watt stick on heater pad from Wolverine heater.com. In the interest of running as high of a blend of biodiesel as possible through the winter. I also have a fuel filter heater to install.

I put the tank heater on yesterday. It gets HOT. My question is how long is too long to leave it on. It got down around 34 last night and I plugged it in this morning about an hour before I left and it did a fine job warming the tank. I'm thinking I can put it on a timer and have it run for 1-2 hours depending on the overnight temps (car is in the garage).

My concern is this heater pad is designed for oil pans. The flash point of B100 can be anywhere from 200-300F. I want to err on the safe side, I have no idea what 500 watts means in terms of heat generated and am looking for some input. I'm also going to insulate the fuel lines.

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Old 10-20-2008, 12:45 PM
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A very useful and relatively inexpensive tool (a must for bio/oil burners) is an infrared thermometer. My first one costs $100, but I recently bought one for $19.00 ($9.00 on sale) at Harbor Freight. Probably isn't as good as the expensive one, but plenty good enough. Somewhere in the 160 -180 degree range is good. I'm surprised to read that bio can combust at 200 degrees. I have often heated mine (not in my car) well above that temp with no ill effects that I can discern.
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  #3  
Old 10-20-2008, 12:45 PM
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An hour or two should not be excessive. More important is that the hot part of the heating pad be mounted as low as possible on the tank so that it always contacts the metal tank where it is covered by fuel. You want to heat the fuel, not the air.

An additional note is always to keep the tank as full as possible. The thermal mass of fuel in the tank, in the middle of the car, somewhat insulated by the rear seatback and stuff in the trunk, and in a garage, will slow the rate at which the fuel loses heat.

On that note, it would be interesting to read the results of your tests in which you put a flexible temperature probe down your fuel filler neck and monitor the temperature in the morning. A cheapie from Radio Shack would dissolve in the biodiesel eventually but would last overnight, I bet.

Jeremy
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2005 E320 CDI . . 113,000 miles My car
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Old 10-20-2008, 12:48 PM
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Fire in the hole!

Quote:
Originally Posted by John Schroader View Post
. . . I'm surprised to read that bio can combust at 200 degrees. I have often heated mine (not in my car) well above that temp with no ill effects that I can discern.
I agree. I did an experiment in which I poured biodiesel into an old cookie sheet (to provide maximum surface contact with the air) and heated it with a MAPP gas torch. It took several minutes in still air before I was able to get the biodiesel to burn on its own. I have the video somewhere.

Jeremy
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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970
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  #5  
Old 10-20-2008, 01:01 PM
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Quote:
I'm surprised to read that bio can combust at 200 degrees. I have often heated mine (not in my car) well above that temp with no ill effects that I can discern.
That is the flash point, the lowest temperature at which it can form an ignitable mixture in air. It will not combust unless there is an open flame or a heat source above its autoignition temperature AND a suitable air/fuel ratio.

G@soline has a flash point of -40°F and Diesel 143°F for comparison.
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Old 10-20-2008, 01:21 PM
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No...I think that flash point for Diesel is wrong Forced. I think its more around 200F IIRC. I do know that it is above 151 because that is the cut off point for DOT between a Flammable liquid and a Combustible. And I seem to recall it being near or slightly above 200F in the past.


But... your point remains the same really. It will not ignite at that temperature unless something else enters into the matrix.
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  #8  
Old 10-20-2008, 01:27 PM
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The Wiki reference to 210F sounds right to me...

Carry on.
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  #9  
Old 10-20-2008, 01:28 PM
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The wiki reference is 210*C for the autoignition temperature.
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Old 10-20-2008, 01:36 PM
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Ah yea... sorry, I am old and even slow too... I knew I recalled a number there though. Could have sworn it was well above 150F. But again... doesn't change your point at all from before.
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  #11  
Old 10-20-2008, 01:55 PM
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210 Celsius is 410 degrees Fahrenheit. The auto ignition point is, in fact, way above 150 F.

Back to the tank. Is it a plastic or steel tank? I would be concerned about slapping a pad heater on a plastic tank.

-Jim
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  #12  
Old 10-20-2008, 06:18 PM
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AFAIK, all 124s have steel fuel tanks.
__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970
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  #13  
Old 10-20-2008, 06:53 PM
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http://www.warehouseautoparts.com/Specials/Kat/Kats_24150_Silicone_hotpad_oilpan_heater.htm

This is a link to a 150 Watt heater pad. At the bottom of the page is a table that shows what size to use with each tank.

I think I have to agree that the 500W is probably too big. Your idea of putting it on a timer will help. Because of the tanks location inside of a well insulated car I would go for the 150W heater. This all depends on where you live. I live in Tennessee, not Canada.

The next thing you have to worry about is the lines under the car. A small electric fuel pump going from the supply to the return line in the engine bay would recirculate the fuel to get the lines hot also. This would also help offset the oversized heat pad by giving a place for the heat to go.

-Jim
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  #14  
Old 10-20-2008, 07:51 PM
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Thanks for the replies, I agree I need to keep the tank as full as possible. I mounted the pad on the left side lower, yes the tank is metal

Thats a good idea about dropping a temp probe in the fuel filler and see how long it takes to heat up. I live in PA just north of Phila. Its not that its that cold, I just want to run as high a blend of biodiesel as possible. I work from home 4 days per week, if I need to be out when its real cold I'll blend some kero in.
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  #15  
Old 10-20-2008, 07:55 PM
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Those are designed to heat up a few quarts of engine oil. If its cold enough to worry about gelling I really doubt it will even get 20+gallons of oil above 100*F unless you leave it on for a few days.

Heat rises so the pad should be mounted on the very bottom of the tank.

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