Ambient air temp & air suspension question

paul102a3 · November 18, 2009, 02:47:18 PM

I have a kind of weird question.

I have owned our bus, MCI 102A3, since April of this year. When the bus is shut down, the suspension stays aired up for at least 36 to 48 hours.

This fall, we hit the northern states (the bus normally lives in Florida) and the suspension would fully deflate in 12 hours or less. At the time, I was thinking I may have a problem but now that the bus is in warm climates, everything is back to normal. The bus airs up and the suspension stays up for 48 hours or so.

There were no issues with the air system while the bus was running (no decrease in purge cycles), just the suspension deflating when the ambient temp was in the 40s to 50s.

Any reason for this?

Paul

Busted Knuckle · November 18, 2009, 03:50:02 PM

Sure it's called cold weather leaks!
Seriously! Most often noticed or associated with coolant issues more often than air, but still same thing.
As the temps drop and the metal parts shrink more than normal the mating surfaces of hoses o-rings and etc. loose their grip and loose a tight seal. Warm things back up and all is normal again.
With coolant leaks it can drive you nuts because once it reaches operating temp it has self healed.
I have seen "new" mechanics spend all day chasing a leak or leaks and not be able to find anything. Then come the next AM after sitting cold all night there it is again a puddle and if you are patient enough drip, drip, drop!

Usually around the turn of the weather experienced fleet mechanics just start tightening all hose clamps, etc. at the first sign of a leak and avoid dozens more in the process!

Air systems have the same issues but usually don't get noticed or much done to them until they are leaking bad enough to cause a problem.

FWIW

BK

belfert · November 18, 2009, 03:54:00 PM

My bus will stay aired up for weeks in the summer. It doesn't even have to drop all the way to freezing before it starts losing most or all air in a day or two.

I asked JD at C&J Bus Repair about this and he said it is pretty common in cold weather.

paul102a3 · November 18, 2009, 03:59:07 PM

Thanks for the info. I do have several small air leaks at the valves to loosen the blower and AC compressor belts that I know of so I am sure there are others. It makes sense that stuff would leak more as things expand and contract.

Just wanted to be sure it wasn't something weird.

JohnEd · November 19, 2009, 05:58:27 PM

Those plastic air line fittings were called out as the prime suspect in previous posts. They are a compression fitting and the plastic tube needs a little tube part put in before the coupling gets put together. I am told that without the tube insert to stiffen the inside wall, they will crap out very early. I have installed a bunch but have no data on leaks that might have developed. No news is good news.

John

junkman42 · November 20, 2009, 08:08:03 AM

I used some fittings that I purchased at a local rubber products supply that have the small inner fitting built into the fitting. The small piece that goes into the plastic hose has ribs so that when the nut compresses the ferrule the ribs grip the inner wall of the plastic hose. The counter man told Me that these fittings were the only fittings that had dot approval. I have had no leaks with these fittings but with the previous fittings with inner piece placed in the tubing after a couple of years the leaks start and I assume it is because of the oring seal in the push in fitting. My experience and unsure of the validity of the dot comment? john

84dime · November 20, 2009, 10:49:21 AM

Finally a subject where i have some knowledge

I 2nd what junkman said, use DOT approved copper fittings. I have ran them on many of my minitrucks (the little trucks with airride suspension) with no problems. Plus they are way easier to change than compression style.

gus · November 20, 2009, 07:24:32 PM

My 4104 has always done this.

However, this fall I noticed that the rear always sags but the front stays pretty much up.

I have replaced all the front bags but none of the rear??

The two rear sag at the same time so I don't suspect the leveling valves, it has to be something in common with both.

One poster a couple of years ago said in cold weather it is caused by the bus trying to level when parked but it now drops the rear even when level??