MC8 Fuel gauge measures auxiliary fuel?

windtrader · September 27, 2020, 12:29:05 PM

It seems the fuel gauge in the dash of the MC8 measure fuel in the main tank and not the auxiliary, is that correct?

The maintenance manual I have does not show fuel lines nor discussion about how auxiliary tank is connected to the main. Hardly any mention of the aux tank at all.

Oh - one other options buzzing around is the fuel gauge is pretty lively, often doing a jitter here and there when catching a little road. I have thought about watching until it really slows or just stops then hitting the station, kind of playing chicken with the bus but not enough nerve in the bank as yet.

thomasinnv · September 27, 2020, 01:47:42 PM

The auxiliary tank is connected to the main tank through hoses connecting to the top and bottom of both tanks. The fuel level is the same in both tanks at all times so the fuel gauge shows the level of both tanks.

ol713 · September 27, 2020, 03:06:28 PM

Hi;
The aux and main tanks are connected with lines running
beneath the bus. They run under the baggage bay. Check
to see if they are leaking.

Good luck, Merle

windtrader · September 27, 2020, 03:58:02 PM

The factory manuals states fuel capacity as US gallons of 144 for main and 35 for auxillary. 179 total.

If gauge is accurate than 1/4 should indicate about 45 gallons in the tank. I added 120 gallons so about 165 onboard, maybe it isn't that far off and that the gauge accounts for fuel in both tanks.

dtcerrato · September 27, 2020, 07:30:46 PM

Be careful considering the fuel tank "capacity" as accurate in the amount of liquid fuel it will hold. The "capacity" is the actual physical size of the tank but the amount of liquid fuel it will hold is less. Example: On GM vintage buses the PD4104 main tank is 140 gal capacity but it is difficult to get more than 110 gallons in it. On the auxiliary tank it's capacity is 26 gallons & at 19 gallons of liquid fuel it's coming up the filler pipe. Don't know about MCIs or more modern buses but in our buses hay day engineering & safety were very stringent. In the case of fuel tanks there was plenty of vapor space above the fuel by design and inlet piping design that made it nearly impossible to "top a tank off". Just saying...

chessie4905 · September 27, 2020, 08:09:10 PM

vapor space? My 4905 is filled 4 to 6 inches down fill neck. No leaks.

dtcerrato · September 27, 2020, 08:37:10 PM

4 to 6 inches for the square area of the tank is quite a few gallons.

windtrader · September 27, 2020, 09:16:53 PM

I hate mysteries but hate more to have to reprime a MCI fuel system after running it dry to see how much it really takes to fill up? lol

someone else surely has heard a reliable number for an MCI after running out of diesel, oops - just say you heard it somewhere from a reliable source, not you naturally.

chessie4905 · September 28, 2020, 04:27:28 AM

The top of the tank is completely covered by three or 4 inches. No "vapor" space. Vapor space is for gasoline. All diesel needs is a slight amount of expansion space. Although if tank is sealed, the tank will handle it as it expands too.

dtcerrato · September 28, 2020, 05:17:06 AM

Vapor space was a bad choice of words. Basically what I'm saying is there is a fair amount of space between the fuel & the top of the tank upon "FULL" as we know it at the fuel pump and the fuel tank "capacity" includes that space.

richard5933 · September 28, 2020, 06:02:52 AM

Federal rules prohibit filling a tank to more than 95% of liquid capacity. Has been that way for decades. Says so on the sticker on my fuel door.

My tank has a liquid capacity of 165 gallons. The federal limit would be about 156 gallons.

luvrbus · September 28, 2020, 07:41:51 AM

Tanks have a useable full level your gauge is not that far off the only way to empty the tank is drain it,they have 10% fuel left in the tank even if the engine starves for fuel

chessie4905 · September 28, 2020, 08:43:03 AM

Drive your coach a few miles and and it'll suck up that 10%.lol

luvrbus · September 28, 2020, 08:57:31 AM

Quote from: chessie4905 on September 28, 2020, 08:43:03 AM
Drive your coach a few miles and and it'll suck up that 10%.lol

That won't happen with a MCI lol it will just die with fuel left in the tank

chessie4905 · September 28, 2020, 10:23:32 AM

When I removed tank in 04, I added fuel 5 gallons at a time till fuel gauge registered. As cheap as an electric fuel pump is, I'd think many should consider adding one for priming. Save wear and tear on batteries and starter regaining prime.