Volvo Penta MD22 - smell of burnt rubber at high revs

[SALLY]

I have an MD22 in my Cromarty 36 motorsailer (made by Blondecell in Lymington, 21 years ago). It ran perfectly for 20 years, until recently I started smelling burnt rubber whenever I rev the engine over 3000 rpm. The smell comes out of the exhaust pipe. This winter, I have put a new collecting elbow after the heat exchanger manifold (not sure if this is the correct term in English, but it's part nr. '7' on the drawing), I have changed the impeller and I've renewed the distribution belt. Moreover, I also had the heat exchanger serviced to keep the small cooling pipes wide open.

I have also renewed the hose that leads from the elbow to the silencer. It had some charring, so I replaced it with a new one too. But to no avail: the burnt smell is still there when running over +3000 rpm. There is also light grey smoke coming of the exhaust then.

Water flow from the exhaust is fine, and the engine is staying at it's normal temperature all the time.

What else can I do, and is there a risk of fire?

[gonzo]

Light grey smoke is usually oil. It would not be unusual for an older engine to burn oil.

[SALLY]

Originally Posted by gonzo

Light grey smoke is usually oil. It would not be unusual for an older engine to burn oil.

It has been emitting smoke of a light grey color for the last few years, but the oil consumption is negligable, so I don't really worry too much about that. It's the smell of burnt rubber that bothers me, especially since I've changed everything that I thought could be responsible for this smell, but to no avail. I'm puzzled what to do next now.

[gonzo]

Is the smell coming from the exhaust end?

[Frosty]

Although you say water flow through the exhaust is fine, I suspect that might not be correct and it be insufficient causing your rubber connector to burn.

Check your impeller.

[kenJ]

Make sure you check the exhaust manifold #7 and especially the nipple where the raw water enters. Many times they carbon up and reduce the amount of cooling water mixing with the exhaust. On some older Yanmar models the coking is so bad it is easier to change the exhaust elbow rather than trying to clean it. Now that you are starting to burn a little oil, it may be amplifying the fouling problem.

[anthony goodson]

I'm with Frosty on this one. Your engine is a Perkins Prima which runs fairly cool anyway,the engine temperature may stay ok even with insufficient water flow to cool the exhaust, so check all pipes on the raw water side and all rubber conections on the exhaust ,if you can smell burning rubber ,there will most likely be burnt rubber. Very CAREFULLY feel the temperature of the pipes AFTER the water injection.

[gonzo]

Ideally, you should use an infrared thermometer to check the exhaust pipes temperature.

[anthony goodson]

OK just to be on the safe side get somebody else to very CAREFULLY feel the temperature of the pipes AFTER the water injection.

[SALLY]

There is no smell of burt rubber inside the boat, it's clearly coming from the exterior exhaust just above the waterline. The elbow has been renewed last season, as the old one was indeed coked up with charcoal and oxidized material.

I could have cleaned it, but it looked too bad in my opinion, so I installed a new one, with wide open injection ports. So that cannot be the culprit, as far as I know.

@ Anthony: all the pipes have been renewed too and everything has been reconnected properly. The pipe after the elbow is also brandnew, but I haven't replaced the big hose that runs outward from the silencer (a big stainless steel pot). I cannot imagine that would run hot, being after the silencer pot?

Anyway, as you suggest, I'll carefully feel the temp of both these hoses the next time I go to the boat. Or have my wife do it

[michael pierzga]

Hmm...no smell inside. Is the engine turbocharged ? If so you might have a look around the turbo.


http://www.nathape.com/res/Logoundan...emd22tmd22.pdf

[SALLY]

No, Michael, not turbocharged, just a simple Volvo Penta version of a Perkins engine.

[michael pierzga]

Hmm...Hmmm....Hmmm. If the smell was in the engine room it would be easy to propose a dozen items to check.

Outside the boat ? Cooling water is sufficient ? Hmmm......... Have you used any fuel additives ? Does the engines lubricating oil have any smell when you dip the stick ? Are you loosing any engine coolant ?

Can you borrow an exhaust temperture Pyrometer from an engineer to verify exhaust temp before the water injection jacket. ?

[SALLY]

Originally Posted by michael pierzga

Hmm...Hmmm....Hmmm. If the smell was in the engine room it would be easy to propose a dozen items to check.

Outside the boat ? Cooling water is sufficient ? Hmmm......... Have you used any fuel additives ? Does the engines lubricating oil have any smell when you dip the stick ? Are you loosing any engine coolant ?

Can you borrow an exhaust temperture Pyrometer from an engineer to verify exhaust temp before the water injection jacket. ?

Yeah, only outside, no smell in the engine room whatsoever. Cooling water is streaming very generously from the exhaust (brandnew impeller too). No fuel additives, no smelly oil at the dipstick. There's a slight loss of engine coolant, but I know the culprit: I have to change the part with the arrow on the drawing: it leaks a little.

I have no idea where I could borrow such a temp meter, but I'll look around.

[anthony goodson]

Re loss of coolant ,be aware ,prima's eat head gaskets ,normally between cylinders 1 and 2 ,sincerely hope not but bear it in mind, this will pressurise the cap.