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Popsf15 · 10-23-2018, 07:50 AM

I have 2003 Monaco Signature with the Cummins ISX 525hp. Today I went into the storage bay with the fuel tank and happened to touch the fuel tank while checking my propane quantity. The tank was very hot. I measured temp with my thermal gun and it was 120 F. I had been on the road for about 6 hours. Anyone have any ideas as to what would cause this. Not sure if there is a fuel pump in the tank or the return fuel is some how being heated on the way back to the tank. Any help would be appreciated.

engine103 · 10-23-2018, 09:23 AM

I would be curious also but whats more interesting is this is your first post in six years! I guess sometimes you just need to ask a question. Jim E. OKC

distaff · 10-23-2018, 09:39 AM

Quote:

Originally Posted by Popsf15

I have 2003 Monaco Signature with the Cummins ISX 525hp. Today I went into the storage bay with the fuel tank and happened to touch the fuel tank while checking my propane quantity. The tank was very hot. I measured temp with my thermal gun and it was 120 F. I had been on the road for about 6 hours. Anyone have any ideas as to what would cause this. Not sure if there is a fuel pump in the tank or the return fuel is some how being heated on the way back to the tank. Any help would be appreciated.

How much hotter was the tank than the surrounding parts of the MH, the ambient temperature, and the road surface?

I'm not sure about where the fuel pump is, is it immersed? I can't imagine anything else making significant heat in the fuel tank bay, and if the only thing that was hot was the fuel, I'd be looking at anything with power in the fuel tank.

barmcd · 10-23-2018, 09:57 AM

I'm not a scientist, but let me give it a shot using my college physics class, or at least what I remember from it. The fuel system of the diesel engine uses very high pressure to inject fuel into the cylinder. The temperature of a liquid under pressure rises. Not all of that diesel pumped through the fuel pump is consumed by the engine. Some of it is returned to the fuel tank. The engine itself is hot, so I'm sure some of that heat is transferred to the fuel. How hot is that return fuel? I don't know so I did a web search and found it can be very hot.

Here's a link that might help explain the situation.

https://solutions.letstruck.com/Answ...l+is+very+hot.

almacd1814 · 10-23-2018, 10:02 AM

Quote:

Originally Posted by barmcd

I'm not a scientist, but let me give it a shot using my college physics class, or at least what I remember from it. The fuel system of the diesel engine uses very high pressure to inject fuel into the cylinder. The temperature of a liquid under pressure rises. Not all of that diesel pumped through the fuel pump is consumed by the engine. Some of it is returned to the fuel tank. The engine itself is hot, so I'm sure some of that heat is transferred to the fuel. How hot is that return fuel? I don't know so I did a web search and found it can be very hot.

Here's a link that might help explain the situation.

https://solutions.letstruck.com/Answ...l+is+very+hot.

The fuel pump is on the engine, not in the tank and “yes” the return fuel is going to be hot. The fuel is rolling around inside a hot cylinder head and injectors. Hot fuel is normal!

MRUSA14 · 10-23-2018, 10:05 AM

Yup. That heat is coming from your engine via the return fuel line and it is supposed to be that way.

RescueRamsey · 10-23-2018, 10:07 AM

Was you generator running?

barmcd · 10-23-2018, 10:49 AM

Quote:

Originally Posted by almacd1814

The fuel pump is on the engine, not in the tank and “yes” the return fuel is going to be hot. The fuel is rolling around inside a hot cylinder head and injectors. Hot fuel is normal!

I didn't say the pump is in the tank.

Bookumdanno · 10-23-2018, 11:11 AM

Not sure on your MH, but my diesel truck has a small radiator attached to the frame that the return fuel goes thru to help cool it off. Might check that

stuhly · 10-23-2018, 11:50 AM

All diesel engines return fuel to the tank. The return fuel also cools the injection pump thereby picking up heat. Completely normal for fuel tank to be warm.

super_rep · 10-23-2018, 02:37 PM

Fuel temperature rise is normal. On the Beaver Marquis we used to have, the fuel was used to cool the engine ECM, so yes, depending on how long your continuous drive was, expect the fuel to get hot.

winniman · 10-23-2018, 05:19 PM

This is another reason to not run your tank too low on fuel. The fuel pump uses fuel to cool it. If the tank is run too low, the temperature will rise in the tank, and be less efficient at cooling the fuel pump.

Ivylog · 10-24-2018, 05:55 PM

Had the fuel hose at the tank start to let air in after a long day getting out of Canada low on fuel. The next morning it was 40 degrees and within the first mile I had a problem getting above 45 mph. Changed filters, filled the fuel tank, replaced the lift pump without solving the problem. Put a clear plastic hose inline before a fuel filter and could see small air bubbles. Removed the fuel tank dip tube...made sure the line was tight before removing. No holes in tube, replaced and put fuel line back on...not as tight as before solving my problem...air in the fuel. This was at 60k miles on a ISL and no problem since. Topping off in Canada would have been cheaper than the 4 days to do all of the above.

palehorse89 · 10-24-2018, 06:10 PM

Quote:

Originally Posted by winniman

This is another reason to not run your tank too low on fuel. The fuel pump uses fuel to cool it. If the tank is run too low, the temperature will rise in the tank, and be less efficient at cooling the fuel pump.

Diesel's love heat, it is what their combustion is based on........the fuel pumps are bolted to a engine that has a operating temperature of 180-200+ degrees and made to operate and perform at those temperatures........the fuel return is to heat the diesel fuel. You can have a full tank of 300 gallons , and in a short period of time it will be warm/hot.........and yes, it does cooling also in the process.