M25 XP Making an "odd noise"

[Sanman]

This weekend while motoring down the ICW we noticed the engine making an odd noise. the noise was very slight and not noticeable from the cockpit, and barely audible from the cabin. but when we opened the engine compartment it became obviously noticeable. It was rhythmic on about a 5 second interval and sounded like something venting pressure, sort of a "Pffffft" noise, like pressing a tire's schrader valve for a second then releasing it. I could not locate the noise specifically. I checked the belt, it was fine, normal tension with about a 1/2 inch deflection, and not rubbing on anything, and I ran my finger along all the fuel lines, nothing there either.

The engine seemed to be running fine, and at normal temp. Just that noise which I don't recall hearing before. Any thoughts?

 

[woodster]

Check your crank case breather pipe

 

[Sanman]

Check your crank case breather pipe

I'll check that this weekend, what would it be indicative of? Thanks!

Anybody else have an idea?

 

[woodster]

it may be loose and leaking the pressure instead of going back in the intake

 

[jrowan]

Gotta tell ya Sanford, that trying to describe & then diagnose a noise via an Internet forum? LOL. But in order to try & be helpful, have you checked your fresh water cooling system, as you have a mark II I assume you have a MX25 engine with fresh water cooling? You likely have a pressure relief valve that may be intermittently tripping, if its building up too much pressure. A pressure relief valve sounds a lot like a tire valve when it trips. Look for steam or water leaks while the engine is running hot & under load. If the engine is not overheating, starts & runs O.K., then I don't think you have a major problem, but noises can take time to isolate & find the source of the problem.

 

[Sanman]

Thanks Guys!
I know its a long shot trying to describe a sound and condition on the forum, but both of these are great answers and give me something to at least check, before I put out the big bucks for a diesel mechanic. I checked the Oil Breather pipe, It was connected, but there HAS been some oil blowing from it, because the end at the air cleaner has some oil residue on the filter. So maybe that was it. I didn't think to check the fresh water cooling and didn't run the engine this weekend under load, so I'll have to wait another week to look at that.
That said; I DID talk to a mechanic, and he concurred that the oil breather would be the most likely culprit. He said that I "Might" need a valve adjustment, but that as long as the engine seemed to be running ok and no overheat condition was occurring (the temp gauge never moved while it was making the noise I originally heard), he said he thought it wold be ok to run it on short trips...since I dont plan on motoring more than 5 to 10 miles at a time, and even LESS if i can ever get some good wind then I plan to get with him in September to do a full check. So Thanks again for the Ideas/info!