Newbie. How to supply more air to my engine compartment.

[scottie]

I suspect that the reason engine room fans have become standard is to clear the air and ideally before starting.
There are few fans as efficient as a Diesel engine for collecting the surrounding air and converting it into heat
The md6 is a seawater cooled engine and as such will run under 70' normally
I do not understand the original reference to a heat exchanger but assumed it to be the exhaust manifold.

 

[lw395]

The main reason modern AWBs tend to have fan ventilation of the engine box is to stop the interior smelling of diesel.
The engine is suppposed to be fairly hot. The thermostat should be keeping it at the right temp.
When it's working hard, a little bilge blower won't shift anything like enough air to lose even a fraction of the waste heat.
You can get cheap digital temperature sensors these days.
It may be worth putting some numbers to the problem.
What is the engine block temp? head temp? air temp at the bottom/middle/top of the box?

The one thing that might need more/cooler air might be the alternator, if you are working it hard. That probably has a fan in it that makes the bilge blower look like a toy.

 

[geem]

The main reason modern AWBs tend to have fan ventilation of the engine box is to stop the interior smelling of diesel.
The engine is suppposed to be fairly hot. The thermostat should be keeping it at the right temp.
When it's working hard, a little bilge blower won't shift anything like enough air to lose even a fraction of the waste heat.
You can get cheap digital temperature sensors these days.
It may be worth putting some numbers to the problem.
What is the engine block temp? head temp? air temp at the bottom/middle/top of the box?

The one thing that might need more/cooler air might be the alternator, if you are working it hard. That probably has a fan in it that makes the bilge blower look like a toy.

I would add that IMHO the ideal set up is to have a very well sealed engine space with extract from the top of that space. The inlet air to the engine can then be controlled rather than relying on infiltration through cracks everywhere. Ducting cool air from the bilges to the alternator would be best. As you say, alternators really benefit from the cool air. Installing smart regulators to get more out of alternators without this cool air supply can lead to problems with the smart regulator such as it shutting down on high temperature or simply cooking the alternator.
We have a large 250cfm extract system that runs at 10amps/12v in our engine room. Keeps the boat smelling sweet and makes a dramatic difference on engine space temperature. I appreciate that everybody doesnt have the luxury of the space we have to install an efficient extract system but the principals carry throigh to smaller installations. Other items in the engine room benifit from the cooler comditions. In our case we have the autopilot drive and brain for the autopilot. The autopilot drive has its own cooling fan blowing over the motor case. This drops the case temperature considerably in addition to the general extract system

 

[oldharry]

Ah! The joys of predictive text.

 

[NormanS]

But running an extraction fan to suck air out of the engine space, while the engine is sucking it in, is pointless.

What is your technical arguement for this comment? Are you a qualified ventilation expert? Do you design these systems for a living? Please clarify this remark so we all understand the basis[/QUOTE]

Common sense, dear boy, common sense.
In your case with a large boat with powerful engines, you probably need extraction fans, and to counteract that, you probably have a turbo on the engine. The OP has a tiny 10hp engine.

 

[geem]

What is your technical arguement for this comment? Are you a qualified ventilation expert? Do you design these systems for a living? Please clarify this remark so we all understand the basis

Common sense, dear boy, common sense.
In your case with a large boat with powerful engines, you probably need extraction fans, and to counteract that, you probably have a turbo on the engine. The OP has a tiny 10hp engine.[/QUOTE]
No turbo, one engine that lives in a nice cool environment and a sweet smelling boat. My generator is 10hp and that gets the benifit of good extract and nice cool air as well

 

[lw395]

Also bear in mind some boats have huge amounts of sound insulation and some have little. That affects heat build up in the engine compartment too.
In the Carribean, you probably don't want the engine heating the interior of the boat.
In the UK it's usually a good thing.

The OP should be asking himself is the engine really too hot? and if so, why?
I'd want to be sure the water cooling was right before thinking about forced air in the engine box.
Engines are not meant to be cold. Neither are they intended to overheat.
Forced air might cover up low water flow when the engine is not working too hard, but the cooling system needs to be good for driving into a headwind and chop.

 

[sailorman]

I would add that IMHO the ideal set up is to have a very well sealed engine space with extract from the top of that space. The inlet air to the engine can then be controlled rather than relying on infiltration through cracks everywhere. Ducting cool air from the bilges to the alternator would be best. As you say, alternators really benefit from the cool air. Installing smart regulators to get more out of alternators without this cool air supply can lead to problems with the smart regulator such as it shutting down on high temperature or simply cooking the alternator.
We have a large 250cfm extract system that runs at 10amps/12v in our engine room. Keeps the boat smelling sweet and makes a dramatic difference on engine space temperature. I appreciate that everybody doesnt have the luxury of the space we have to install an efficient extract system but the principals carry throigh to smaller installations. Other items in the engine room benifit from the cooler comditions. In our case we have the autopilot drive and brain for the autopilot. The autopilot drive has its own cooling fan blowing over the motor case. This drops the case temperature considerably in addition to the general extract system

Start from first principles, keep the engine clean & sweet

 

[NormanS]

Common sense, dear boy, common sense.
In your case with a large boat with powerful engines, you probably need extraction fans, and to counteract that, you probably have a turbo on the engine. The OP has a tiny 10hp engine.

No turbo, one engine that lives in a nice cool environment and a sweet smelling boat. My generator is 10hp and that gets the benifit of good extract and nice cool air as well [/QUOTE]

I don't know how you managed to make it look as if it was me who said, "What is your technical........"
A 1 litre engine running at 2000 rpm will draw in 2 cubic metres of air per minute. Seems like pretty good ventilation to me. If you the introduce further extraction, thereby reducing the atmospheric pressure in the engine room, you really need to derate the fuel injection to suit, unless you fit a turbocharger. Overkill.

 

[lw395]

.......
A 1 litre engine running at 2000 rpm will draw in 2 cubic metres of air per minute. Seems like pretty good ventilation to me. If you the introduce further extraction, thereby reducing the atmospheric pressure in the engine room, you really need to derate the fuel injection to suit, unless you fit a turbocharger. Overkill.

1 cubic metre if it's a four stroke...
A cubic metre of air has a heat capacity of about 1.2kJ per degreeC IIRC
So if it's 10 degreeC outside and 90 in the engine box, that's about 96kJ per Cubic metre. 96kJ per minute is 1.6kW.
Your 10hp/7.4kW engine if it's 45% efficient will be needing to lose about 9kW in heat at full chat.
But pottering about the cooling from the air can be significant.

 

[prv]

I don't know how you managed to make it look as if it was me who said, "What is your technical........"

The two of you keep posting messages with broken

tags. Look at your own message #29 - you've made it look like "No turbo, one engine..." is your own new text, instead of someone else's quoted. If someone now hits reply and doesn't fix your mess first, they'll quote you as having said that.

Pete

 

[Tranona]

I think its a CE requirement these days

Yes, its purpose is to extract fumes, not cool the engine box. As already mentioned the engine draws far more cold air in than a puny little electric fan will move.

My old and new Bavaria have almost identical engine compartments and engines. The old one did not have a fan, the new one does. Have not noticed any difference in temperature in the compartments.

 

[Tranona]

Engine overheating solved, I believe, but engine bay still gets hot and any clothes worn on the boat have a dieselly smell to them. I've read somewhere that the engine bay shouldn't be higher than than 140 otherwise the alternator is effected. Glad of the heat in the winter but want to make sure I'm not damaging the engine in the summer. Will try and get some temp figures for the engine bay after a good run.

What you are describing is perfectly normal. An ancient seawater cooled Volvo is a a noisy, smelly old thing which (if the cooling system is in good nick) should run at around 70C. You should have no problem running at maximum revs as the seawater keeps it coll. Unlikely it will ever get the compartment up to 140C, in fact unlikely to ever get above 70 - which seems hot when the ambient temperature in our climate rarely exceeds 30.

As mentioned by several others, the purpose of the extractor fans is to remove fumes, not increase air flow or reduce compartment temperature. The fan should be high up at the back of the compartment and exit through trunking high above the waterline. You might also look to see if you can open up the area into the bilge so that the engine can draw in more air. The increase in air flow particularly with a forced outlet may reduce the smells but will have minimal effect on compartment temperature. Big lump of hot cast iron in a confined space will get hot!

 

[sailorman]

Yes, its purpose is to extract fumes, not cool the engine box. As already mentioned the engine draws far more cold air in than a puny little electric fan will move.

My old and new Bavaria have almost identical engine compartments and engines. The old one did not have a fan, the new one does. Have not noticed any difference in temperature in the compartments.

I am aware of that

 

[Heckler]

We're discussing a 28' yacht with a little 10hp engine. (Which is what I have, incidentally) and you're saying it needs cooling fans? Don't be ridiculous.

Your dislike of me is such that it is colouring your common sense, the OP asked about cooling fans because he has concerns about the heat being developed in his engine space. I, along with rational others, am attempting to give him some advice based on our real life experience and what manufacturers are doing. So why dont you go and,as the Scots so elequently say, go and boil yer head!
Stu

 

[Tranona]

Your dislike of me is such that it is colouring your common sense, the OP asked about cooling fans because he has concerns about the heat being developed in his engine space. I, along with rational others, am attempting to give him some advice based on our real life experience and what manufacturers are doing. So why dont you go and,as the Scots so elequently say, go and boil yer head!
Stu

Come on Stu! This is a little 10hp donk and has run satisfactorily (just like thousands of others) for 30 years. Nothing unusual about the set up.

As you will see above, the fans fitted to your Benny and my Bavaria do little to (if anything) to reduce engine compartment temperature. They are fitted because of the RCD requirement that originally came from the ABS to remove fumes.

So parsifal is right - current practice has little bearing on the OPs issue, although as I suggested an extractor fan might help with the fumes. Incidentally I ran a little 10hp seawater cooled engine in a confined space for 25 years. Always felt hot down there but never overheated and always able to run to maximum revs. Fortunately not a smelly old Volvo!

 

[michaela]

Hi Guys. Yes you are right I did mean exhaust manifold.
Some of the posters are getting as hot as my engine, I suggest increased lubrication with tea and or alcohol, but the discussion has raised a number of very interesting points.
What I will take away from this is that in my current set up to ensure a greater air supply I could fit some sort of closeable louvre at the top of the cabinet. If the water gets over this I'm in serious trouble.
The question of cooling water volume supplied to the block is an interesting one. I changed the engine water filter to a clear top vetus filter and there does not appear to be any restriction in the supply part of the system. However I don't have any idea of typical volumes that this should be pumping through. It certainly isn't a water festival coming out of the exhaust. But any time I have held my hand over the exhaust the water is not exactly hot so I assume that the flow through of water is sufficient.
With the new louvre in place I will see if there is any appreciable difference in engine cabinet temperature. If not I will have to assume that the problem is not air supply.
The exhaust smoke does have a grey hue to it. I have assumed that this is because the engine is 40 years old.
If I assume that some of the exhaust and cylinder head cooling ports are blocked or partially blocked then it would be nice to do a decoke. Ideally it would be good to do it without removing the exhaust manifold again.
In terms of insitu decoking I have read of people passing some sort of dilute acid through the system. Sounds a bit risky not to mention the discharge into the environment. Anyone got any experience of running any solutions through their engines, and the outcome.

 

[Poignard]

Your dislike of me is such that it is colouring your common sense, the OP asked about cooling fans because he has concerns about the heat being developed in his engine space. I, along with rational others, am attempting to give him some advice based on our real life experience and what manufacturers are doing. So why dont you go and,as the Scots so elequently say, go and boil yer head!
Stu

Are you really an engineer or just masquerading as one?

 

[Lucky Duck]

Yes, its purpose is to extract fumes, not cool the engine box. As already mentioned the engine draws far more cold air in than a puny little electric fan will move.

My old and new Bavaria have almost identical engine compartments and engines. The old one did not have a fan, the new one does. Have not noticed any difference in temperature in the compartments.

I am aware of that

If that is the case I'm surprised my current (2015) and last (2005) boats didn't have an engine bay fans fitted, only the Beneteau before that (2001) had such an installation.

 

[michaela]

Hi Tranona sorry I meant 140 F as an idealised maximum engine compartment temp (60 C).
Yes perhaps I should accept that this is how these engines run. I suppose I'm just trying not to run it in a bad way, or a way that will shorten its life