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Old 30-03-2011, 02:07   #16
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Re: Exhaust smell of burnt rubber with Volvo MD22

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Originally Posted by Artif View Post
Being as you have checked the heat exchanger, you might want to check the hoses etc on the rest of the sea water cooling circuit, especially as this is a recent problem.
You might have a piece of impeller blade stuck in the pipe work or a collapsed hose somewhere or a corrosion blockage, which is reducing the flow slightly, hence only having the problem at high revs.
I just changed al the hoses, so I'm sure there's nothing in there. The impeller is a new one too, and the old one was in perfect shape, so no debris there either. (I kept it as a spare for emergencies).
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Old 30-03-2011, 02:12   #17
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Re: Exhaust smell of burnt rubber with Volvo MD22

Cromarty said that he normally only uses 3000 rpm when he is manouevring. That would suggest for only short periods, which IMHO would not cause a drastic temp increase. He also suggests the water flow drastically increases at higher revs. Cromarty - have you checked the belts on your engine. Perhaps they slip at higher revs - and last time that happened to me - they smelled pretty bad. Just a passing thought.
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Old 30-03-2011, 02:27   #18
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Re: Exhaust smell of burnt rubber with Volvo MD22

That's correct. I notice the smell even when I rev up for a very short period, for instance to stop the boat off. Of course it also occurred last week, when I made a longer test drive at 3000 rpm after the rehaul. I also thought about the belts, but they are all in good order and tension, and if it would be a belt, I'm sure I would also smell the burnt rubber in the engine room, which I don't. The smell only comes from the external exhaust pipe. Very confusing!

Of course, I could just neglect it, but that's not my attitude: if I smell something burnt, I want to know what is burning or heating, so that I can fix it. I want to cruise with peace of mind.
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Old 30-03-2011, 02:45   #19
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Re: Exhaust smell of burnt rubber with Volvo MD22

Sounds very much like a cooling water issue, you will need to check the exhaust temperature when running at high revs/load, make sure you check the whole length of the exhaust.
Check your entire seawater cooling system, from skin fitting to exhaust elbow, you might be confusing high water flow in the exhaust with the extra velocity of the exhaust gasses pushing the water at high speed.
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Old 30-03-2011, 03:13   #20
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Re: Exhaust smell of burnt rubber with Volvo MD22

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...you might be confusing high water flow in the exhaust with the extra velocity of the exhaust gasses pushing the water at high speed.
That's quite true, of course. It LOOKS as if there's more water at high revs, but it might also be a higher exhaust speed, as you point out. But if the cooling water flow would be inadequate, wouldn't the engine run hot after some time? I can run it for hours without problems...
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Old 30-03-2011, 03:22   #21
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Re: Exhaust smell of burnt rubber with Volvo MD22

The engine may not run hot, the cooling systems on marine diesels are often well over spec, to allow for closed environments i.e in a box in the bilge of a boat, compared to a vehicle engine with a high airflow in and around the engine bay.
I've come across numerous engines that appeared to be in good running order, until I work on the cooling system and find the coolers 1/2 blocked or impellers with blades missing etc.
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Old 30-03-2011, 03:34   #22
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Re: Exhaust smell of burnt rubber with Volvo MD22

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The engine may not run hot, the cooling systems on marine diesels are often well over spec, to allow for closed environments i.e in a box in the bilge of a boat, compared to a vehicle engine with a high airflow in and around the engine bay.
I've come across numerous engines that appeared to be in good running order, until I work on the cooling system and find the coolers 1/2 blocked or impellers with blades missing etc.
Well, in fact I just checked and repaired the complete raw cooling water system. The impeller is brandnew, the heat exchanger has been dismantled + serviced and the elbow is also new. The straining filter is clean, the exhaust hose is new... The only thing I haven't been able to check is the water inlet in the hull and it's valve. I'll do that when the boat is on the shore in a few weeks.

But then again, I also smelt the burnt rubber just after the boat went into the water last year, after thorough inspection of the inlet.
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Old 30-03-2011, 03:48   #23
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Re: Exhaust smell of burnt rubber with Volvo MD22

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Well, in fact I just checked an repaired the complete raw cooling water system. The impeller is brandnew, the heat exchanger has been dismantled + serviced and the elbow is also new. The straining filter is clean, the exhaust hose i new... The only thing I haven't been able to check is the water inlet in the hull and it's valve. I'll do that when the boat is on the shore in a few weeks.

But then again, I also smelt the burnt rubber just after the boat went into the water last year, after thorough inspection of the inlet.

I understand that you have replaced the impeller etc. I was giving you examples of where engines appear to working normally, yet had serious problems with the water flow for various reasons.

Are you sure the skin fitting valve is fully opening. Is it a ball valve or gate valve. Gate valves get choked up etc and don't open fully, ball valves can fail to open fully if the handle is loose or the shaft gets worn.
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Old 30-03-2011, 04:12   #24
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Re: Exhaust smell of burnt rubber with Volvo MD22

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Are you sure the skin fitting valve is fully opening. Is it a ball valve or gate valve. Gate valves get choked up etc and don't open fully, ball valves can fail to open fully if the handle is loose or the shaft gets worn.
It's a ball valve and I'm planning to replace it when the boat is out of the water. Handle is tight enough, but the valve leaks slightly. So time to replace it anyway. Perhaps that's the culprit, we'll see. Appreciate the advice!
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Old 30-03-2011, 08:30   #25
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Re: Exhaust smell of burnt rubber with Volvo MD22

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Certainly on the face of it everything seems normal from my limited experience.

I may be learning something about "mixing" now. I would have thought if the flow increases substantially at higher revs then everything is good. Now I suspect that the mixing implies the water and gas become a more homogenous blend than when not mixing well.

So possibly the water and exhaust are passing through to the rubber hose in separate streams? The unmixed stream of exhaust being hotter at high revs and burning the hose?

I was thinking that merely turbulence in the mixing elbow is the mechanism at work here. Is there something more to this, psneeld?

Forgive me for continuing to butt into the discussion, just trying to learn.
Yes.... the water is supposed to get injected into the exhaust evenly or more on top so that the hot exhaust gas is cooled enough to not burn the hose...

You can check if the flow looks OK by taking a water hose and hooking it into the injection nipple where raw water would come from the pump/exchanger/etc...if it looks to be coming out the holes evenly based on the size of the holes...then amount of flow has to be the problem...but if uneven and less on top...that could be the reason for the hot rubber...

Not sure if I said it earlier...are you just getting a smell or are you actually cooking the hose? If you haven't checked, you might want take the hose off and look inside.
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Old 30-03-2011, 12:04   #26
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Re: Exhaust smell of burnt rubber with Volvo MD22

Well, I've been to the boat today and did a few more checks. I let the engine run warm to normal operating temperature (85 C). Then revved it up to 3000 rpm for a few minutes so I got the smoke and the smell.

A few remarks:

- My wife, who sees colours better than I do, says it bluish grey smoke.
- the exhaust water (outside the boat ) is very cool and abundant
- the elbow stays cool to the touch, approx. 25C
- the rubber hose stays cool to the touch, approx. 20C
- engine stays at normal operating temperature
- no leaks anywhere
- some traces of diesel oil (or oil?) in the dock

My temporary conclusion: the rubber smell is certainly not the exhaust hose. Everything in the exhaust line is nice and cool. Where is that smell coming form. The mystery stays...

Would adding some additive to clean the injectors help?
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Old 30-03-2011, 12:25   #27
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Re: Exhaust smell of burnt rubber with Volvo MD22

Does the smell of burning rubber indicate a brain tumour? - Yahoo! UK & Ireland Answers
I know Volvos usually give me a headache.

Would adding some additive to clean the injectors help?

I doubt it, you would be better off having the injectors serviced.
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Old 30-03-2011, 12:38   #28
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Re: Exhaust smell of burnt rubber with Volvo MD22

Now you got me really worried, as a die-hard hypochondriac! But then again, wy wife and friends smell it too and there's one chance in a million that we would all have a brain tumor at the same time.

But, as we all know, the Volvo MD22 is a Perkins engine, and that peace of equipment already gave me headaches in the 80-ies when I was sales & marketing manager for British Leyland Belgium, trying to convince our poor dealers to sell more Maestro's and Allegro's.

But I'll try the additive, it doesn't cost much and it won't do much harm I guess.
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Old 30-03-2011, 12:46   #29
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Re: Exhaust smell of burnt rubber with Volvo MD22

Maestro's and Allegro's, you have my deepest sympathy, and my apologies, for coming from the same nation that produced them.
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Old 30-03-2011, 12:59   #30
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Re: Exhaust smell of burnt rubber with Volvo MD22

Not to worry, ever since I sail my beloved Cromarty 36, produced in the same country that made the damned Perkins, I have forgiven you lot. The best boat money can buy (in it's class), and indestructible. Except for the engine, that is.

Although, to be honest: this Perkins served me perfectly for 20 years now, and it has always been very simple to maintain and service. If it wasn't for that rubber stench, I'd say it's a jewel.
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