How hot is your engine compartment?

[Danny Jo]

Last winter I put a temperature probe (from a cheap Aldi maximum-minimum thermometer) in the engine compartment to check that my antifrost heating arrangements were working. I never got round to removing it, so by accident I have discovered that the temperature in the compartment on a decent run at cruising revs (2400) is a pretty constant 57 degrees Celsius.

The sound insulation is nominally fireproof, finished on the inside in reflective foil and fitted (ahem) without any gaps in the angles or joins, so it is presumably also acting as thermal insulation. The engine, a Yanmar YM30 just over 2 years old, runs like a dream, the oil seems pretty clean at the 150 hour oil changes, and the raw water coming out with the exhaust is barely tepid.

This is of course another example of the peril of measuring something without a standard against which to compare it - you get something else to worry about. Should I be worried?

 

[michael_w]

My extractor fan makes a fine hand warmer on cold night watches.

 

[monkfish24]

Of course not, the only thing a little warmth in your engine bay is going to create is warmer fuel which means better combustion which means better economy..... /forums/images/graemlins/grin.gif

on a more serious note, as michael pointed out, why not draw the warm air away to the cabin through some ducting, that way you'll get 57 degree air drawn from the engine when it's running and warmed up

 

[savageseadog]

The main effect of a warm engine compartment is that air, if drawn from in there, will be less dense. Less dense means less oxygen which means less maximum power. It's the reason that cars are fitted with intercoolers.

 

[claudio]

I tested mine out recently and fastened a temperature logger up high in the engine room. The maximum temperature attained was 42 deg C. I had the engine room blower running continuously. The engine room is well insulated too. The engine is a Perkins 135hp. Revs were kept below 2000 RPM

 

[NorthUp]

Betamarine blamed excessive alternator vee belt wear on their small engines on excessive engine bay temperatures a few years back- cannot remember the figures though.
A quick google gives a recommended max of 70 deg C for Fenner, as an example.

 

[monkfish24]

[ QUOTE ]
The main effect of a warm engine compartment is that air, if drawn from in there, will be less dense. Less dense means less oxygen which means less maximum power. It's the reason that cars are fitted with intercoolers.

[/ QUOTE ]

he he forgot that inboards take the air from around them /forums/images/graemlins/blush.gif

 

[MM5AHO]

38C

 

[Danny Jo]

So if I need to wack the power up to max in order to make progress against a strong head wind I had best lift take the cover off the engine compartment.

I had previously noticed that the engine compartment was still warm twelve hours or more after stopping. This made starting easier with the old Perkins, and I wonder if it also provides some protection for the new engine from the condensation that is said to occur during rapid cooling?