engine box ventialtion fan

[Bosun Higgs]

my engine is very closely boxed in and I am getting alternator problems which the experts put down to lack of cooling. There is a cold air feed to the engine so I would like to fit a fan into it to improve cooling. Where can I buy a small engine ventilation fan?

 

[michael_w]

ASAP supplies and the like. The clamshell sort are usually quieter than the in-line variety. On my boat the ducting starts at the top of the engine compartment and the discharge is through the aft cockpit coaming. Just wire it in to the engine electrics.

 

[Spi D]

Mandatory on all petrol inboard installations and should be run from 5-15 minutes before, during, and 5-15 minutes after running the engine.

Plenty models, designed and insulated for the purpose, to choose from. Noise isn't an issue when the engine is running
Make sure you fit the fan to remove air from the engine room - not force fresh air in as it will try to send fumes out allover..

When you are at it, a dedicated fresh-air-to-intake hose will improve performance and mpg.

 

[sailorman]

my engine is very closely boxed in and I am getting alternator problems which the experts put down to lack of cooling. There is a cold air feed to the engine so I would like to fit a fan into it to improve cooling. Where can I buy a small engine ventilation fan?

Do you have a "Smart Booster" fitted, if so that could be the problem

 

[Bosun Higgs]

Do you have a "Smart Booster" fitted, if so that could be the problem

Yes I do but I have switched it off for the last few trips and the problem is still there. I spoke to Charles Sterling about it and he made an interesting comment - apparently 5 or so years ago, alternator regulators stopped being soldered with silver solder and instead used ordinary lead / tin. At high temperatures this is mechanically weak and yopu get dry joints appearing, which would account for my alternator periodically and briefly shutting itself off. It is in fact far too hot to hold your hand on it.

 

[sailorman]

Yes I do but I have switched it off for the last few trips and the problem is still there.

so why should the alternator suddenly over heat, what has changed even the kin weather aint hot

 

[Bosun Higgs]

so why should the alternator suddenly over heat, what has changed even the kin weather aint hot

Thats why I suspect Sterling is right. I replaced the alternator last year - had similar problems with that when using the regulator.

 

[sailorman]

Thats why I suspect Sterling is right. I replaced the alternator last year - had similar problems with that when using the regulator.

I used smart chargers ( Kestrel) when they first came out, car type alternators run too hot with the extra load as they are designed to be "outside under a car", i know the newer ones have temp sensing but i dont trust them. i do not use such devices any more

 

[West Coast]

Hi Bosun - FWIW, have had no charging problems and my alternator is original (certainly predates 2003). Given you and I have the same boat, with same tight engine box, could affirm your suspicions. Engine is a VP 2003, with standard alternator.

Given the tight constraints of the engine box, I think forced ventilation in any event would be a good idea but how to do it?? Will consider this over the weekend when on the boat and advise my thoughts..............

 

[MASH]

What sort of "cold air feed" is provided, where does it come from and go to - and is it forced or just a duct?

I'm wondering if this is purely providing a cool air to the intake or is it for more general ventilation?

The engine swallows maybe a cubic metre of air per minute, and if the performance isn't much affected by breathing warm air (it would be affected to some extent but I wonder how much) then it might be used to create its own ventilation circulation. Making holes in a close fitting engine box will let out plenty of noise which isn't desirable.

My Yanmar installation (which was in no way closely contained) ran noticeably cooler than it became a few minutes after shutdown which I suppose must be down to the natural airflow created by the engine swallowing lots of air - perhaps this can be turned to advantage?

 

[cryan]

My Yanmar installation (which was in no way closely contained) ran noticeably cooler than it became a few minutes after shutdown which I suppose must be down to the natural airflow created by the engine swallowing lots of air - perhaps this can be turned to advantage?

This is more likely that the metal and cooling water in the engine are still absorbing heat from the cylinders yet the cooling water pump will have stopped with the engine so there is no new water to remove the heat. As such the engine will stew slightly in its own juices whilst natural air cooling takes effect. It is for this reason that on bigger engines with externally driven pumps you leave the pumps running for five minutes after shutdown.

 

[Piddy]

I have a little timer box that runs the extractor fan for 40 minutes after the engine is switched off. It works well as the engine compartment isn't sealed so it draws air in from all over the boat.

There is a 4" tube that ducts cool air in but I'd guess as much comes from the bilge as anywhere. It helps keep the hot engine smell out of the boat when motoring and is surprisingly warm as it exits the cockpit coaming.

It has a separate switch outside to disable it should there be a problem but it's worked perfectly for 10 years since fitting.

 

[oldsaltoz]

If you calculate the amount of air a engine draws you will soon realise that a fan will do little or nothing when the engine is running at normal revs, imagine a 4 cylinder 4 stroke engine that pulls in just half a litre per cylinder, with just one firing on every stroke. That's half a litre per revolution, lets say the revs are 1800 RPM, that's 54,000 litres per hour, 900 litres per minute or 15 litres per second.

Three things you can do for very little outlay.
1. Make sure the air can flow freely into the compartment without any restrictions.
2. install a fan, see the fan fitted to you cars alternator.
3. Run a duct from the air intake inside the engine box to the charging device face.

Good luck and fair winds.

 

[Marsupial]

I imagine a 4 cylinder 4 stroke engine that pulls in just half a litre per cylinder, with just one firing on every stroke. That's f you calculate the amount of air a engine draws you will soon realise that a fan will do little or nothing when the engine is running at normal revs,half a litre per revolution, lets say the revs are 1800 RPM, that's 54,000 litres per hour, 900 litres per minute or 15 litres per second.

Please lets get away from the bodge job, let's concentrate not on what "works" but what will work best.

Its not rocket science, manufacturers spent a long time on defining the best way to install inboard engines (in the 1970's I was there) they say fit a fan. Ignor best practise if you like, its a free ish world, but you engine will reward you with longer life and lower running costs for the sake of a correct installation. You will benefit from less fumes in the accommodation spaces.

Question: SO - why does engine compartment temperature drop when a ventilation fan is used correctly?

Answer: because EXTRA cool air is drawn in from outside and EXTRA hot air is exhausted via the fan. The EXTRA is over and above the volume of air the engine inhales.

Question: SO - why does fuel consumption decrease and efficiently increase when a ventilation fan is used correctly?

Answer: because the engine is digesting cooler fresher air.

ADVICE: Do it right - fit a properly sized fan and ventilation.