Community Forums

sailor_lou · 07-27-2010, 08:05 AM

Morning all,

I have a 350HP CAT C-7 engine and recently noticed that when the compressor is running under load, it makes a fair amount of noise. I say “recently noticed” because this is my first diesel and between all the other noises a diesel makes I am not sure if this is new or a sign of a pending issue. It is a mechanical knocking sound, similar to an extremely loud mechanical lifter, that I can hear over all the other engine noises. It stops as soon as I hear the unloaded valve open (air release), but starts again when the compressor is recharging the air tanks. Because of this I am assuming it is the compressor and it is only loud when it is under load. The tanks are being charged as normal (both charge time and pressure), but the noise does appear to be unusually loud to me. Are these things typically noisy?

I realize it’s tough to say it is a problem without actually hearing it yourself, but would be interested in the group’s thoughts and experiences. Also any other ideas, like a problem with a pinched air line or air dryer would be appreciated. I don’t want to just start replacing parts (ie: compressor) until I have a better handle on the cause.

Thx,

Lou
05 Travel Supreme 38DS04
Spartan Mountain Master, CAT C-7

deltastar459 · 09-24-2010, 06:52 PM

I had the same concern as a new diesel owner. Cat advised me this compressor noise is normal.... deltastar459

sailor_lou · 09-27-2010, 04:56 PM

Thanks for the feedback. I had a CAT authorized repair shop check it out and the mechanic that looked at it told me it was noisey than expected and said they would replace it. At first they thought it was beyond warranty (05 motorhome), but since it was originally purchased in 06 they agreed it was stilll covered. The service manager told me the part was on order and I could pick it up in a few days. When I went to pick it up, the service manager told me they listened to it again and felt it was OK and they didn't replace the compressor. I pushed back, but he said there is nothing wrong and that they wouldn't replace it. I find it interesting that when they believed it was on my dime they were eager to change it out.

I still believe there is a problem there, but that they were concerned CAT wouldn't cover it since it hadn't failed (yet). I may just change it myself if it doesn't actually fail before the warranty period expires. In the meantime, I keep listening to every other motorhome I come across to get a feel for how loud they are.

Thx again,

Lou

deltastar459 · 09-28-2010, 10:07 AM

Hey Lou, I have owned my Cat C9 for 3 years next mont. The first year I purchased it I took it to Cat complaining about the excessive noise and they checked it out and asked if I had ever owned a Cat before, when I stated no the advised that this was completely normal. That as I say was 3 years ago ans I still have a very loud compressor but nor problems with it's operation. It is only noisy when engaged. I am now out of warranty, be interesting to take it to a different Cat dealer and see what they say. But again it is working fine...... Deltastar459

sailor_lou · 09-28-2010, 02:54 PM

I am considering that, but the first one charged me $180 (investigation charge) to tell me nothing is wrong. I'm not sure what a new compressor cost but each time I get another opinion it adds up. I'm still thinking of just replacing it.

Lou

94-Newmar · 09-28-2010, 02:59 PM

My 8.3 Cummins w/compressor is sorta loud as well. I can hear it over other noises once I started listening for stuff.

sailor_lou · 09-28-2010, 03:53 PM

Thanks, you guys are making me feel better about the noise. Maybe I'm just being paranoid.

Lou

wagonmaster2 · 09-28-2010, 04:56 PM

Quote:

Originally Posted by sailor_lou

I am considering that, but the first one charged me $180 (investigation charge) to tell me nothing is wrong. I'm not sure what a new compressor cost but each time I get another opinion it adds up. I'm still thinking of just replacing it.

Lou

I also have a Cat C-7 engine and find it's hard to believe that even under warranty a customer gets charged if they think something is wrong with the engine when there isn't. But I certainly do believe these shops will stick it to the customer any time they find an opening. I was charged $450 for a 2 hr 15 min valve adjustment at a Cat shop then they added another $53 labor for changing the fuel filter during that same time period. You'd think $200/hour should cover everything done without adding another $53. I think I'm going to start looking for a different Cat shop but they are probably all the same.

I'll have to start listening for my air compressor's noise. As you stated these diesels make so much noise how can you tell if anything is wrong. When I bought my coach new I asked a Cat/Freightliner shop when to have the valves adjusted and they said not until I could hear the tappet noise. I had to laugh, they aren't like the old Chevrolet 6-cyls that you could hear every tappet, piston slap, wrist pin, or connecting rod that got a little loose.

Good luck on your quest. Keep us informed on your choice.

Wagonmaster2

sailor_lou · 09-29-2010, 05:05 AM

I can understand a charge for their time, even if there is nothing wrong. However, what really bothers me is the first mecahnic spent 15 minutes (with me helping him) and determine the noise was unusually loud and recommended a replacement. Then once the service manager realized it was still under warranty, he made the decision that it's not a problem, charged me an hour and half worth of labor and said I was good to go.

I always do my own maintenance and the only reason it was in the shop in the first place was because it is still under the manufacturer's warranty. I just don't trust the "professionals," so once again, I'll take care of it on my own.

Thanks for the feedback. BTW, I'd would like to meet the individual that can hear a tappet noise on a diesel.....LOL

Lou

tiderv · 06-12-2013, 07:32 AM

Good morning Lou from Mobile, Al. I just read your post on concerning the noise in your Cat C7. I know it has been a while since you posted, but I would like to know if you are still having the problem or found a solution.

I have an '06 Phaeton with the C7, 31,000 miles and having the exact same problem. I have had it checked by 3 different dealers, with none giving a reasonable explanation. I finally replaced the compressor, a very difficult job, with a new one from Cat. I also replace the dryer and check valve, The new compressor was around $1,200. The noise did not change one bit and now I am worried there may be a problem in the timing gear train, but I have no way of knowing. I have driven about 4,000 miles since installing the new compressor and have had no problem so far. I find it very difficult to believe that this noise is normal.

It would be helpful if you would let me know what you have found. My email is bamatiderv@bellsouth.net, if you want to contact me.

Dyno Bill · 06-12-2013, 10:58 AM

My compressor is very loud also, you can almost feel it hammering away. I'm assuming its fine as my coach only has 43,000 miles but I will be watching this thread. 05 cat 300hp.

sailor_lou · 06-12-2013, 02:51 PM

I spent some time listening to other engines in various campgrounds (the owners must have thought I was some kind of nut rushing over when they started up their engines) and noted that some were loud like mine until the unloader valve dumped. Based on that and what others have told me I started to believe this is normal for the compressor. The best explanation I have gotten is the reed switches get louder as they cycle under a heavy load (near max pressure) and that would explain why it's not too bad when the compressor first kicks in.

Although I spoke to CAT, I never did contact Bendix (compressor manufacturer), which I probably should have done in the first place. I was going to do it anyway, but between the lack of space between the block and the frame rail and the hydraulic pump hanging off the back, the job looked like a nightmare so I decided to wait to see if was getting worse. It's been three years and about 17k miles since I first questioned this (engine now has 39K on it) and still seems the same so I'm holding off.

Lou
05 Travel Supreme Envoy

tiderv · 06-13-2013, 08:13 PM

Thank you so much for the information. This has been a real puzzle for me and I guess I am on some kind of quest to find the answer. I did speak to an engineer at Bendix and he said all compressors are somewhat noisier under load and some may be louder than others. He said to be sure the mounting bolts are tight and the compressor is securely mounted. I told him I can say for sure that is not the problem. He said another possibility for excessive noise may be the size of the discharge pipe, if too small could create backpressure and cause the compressor to ping loudly while pumping. I replaced the discharge pipe with a 1" ID pipe, and although it seems to pump up faster, the noise is unchanged. He also mentioned the reed valves and the check valve, but only in passing. As far as I can tell there is nothing left to replace, so I guess it will remain a mystery. You are right, replacing the compressor fits right in the nightmare category and in my case had no effect at all. So far I have spent about $1,500 and many hours chasing this noise. Since you have driven 17K with no problem and have heard others make the same noise, I do feel better that I am not going leave parts all over the interstate.

Please let me know if you find any additional information and I will do the same. Thank you again for the information.

Robbie

sailor_lou · 06-16-2013, 07:04 AM

Robbie,

I understand your concerns, the noise does seem excessive and not knowing if there is an underlying cause is a bit unsettling. However, I'd say you covered it pretty well. I'll check the mounting, but based on what I've seen every time I've been up there with a stethoscope everything looked secure.

Thanks for your post, it helps to accept this is a "normal" characteristic of the compressor. If I hear anything differently or if something changes I'll be sure to get back to you.

Safe travels,

Lou
05 Travel Supreme Envoy
Spartan MM/CAT C7