Actual Engine Room Temperature

[DaleM]

I have a Morgan 40 ketch with a Westerbeke 55c engine (55hp). I sound insulated it with a layer of Hardi board cement board, a layer of Green Glue and another layer of cement board. It is completely sealed off from the cabin and has an air intake opening leading to the cockpit lockers that are vented. I used cement board due to lack of space, using mass/ rubber / mass.

The engine is very loud without sound insulation. It runs at 180F. I have ran it 500 hours like this but mostly during the winter. I ran it for 2 hours yesterday, outside temp was 90F. I opened the engine compartment several minutes after stopping, it would have gotten hotter. The walls were 125F, transmission 150F, engine between 150F and 180F. The transmission has a bolted on cooler.

Should I be concerned? The engine pulls around 70cfm when running. The biggest engine fan that has a reasonable price is 250cfm and it may make no difference. It would be pulling 90F air through an engine room that's radiating heat at 180.

Has anyone installed a fan that has made a measurable temp difference? I would like to hear actual before and after temps not opinions. If I install a fan then I will need to make baffle boxes to feed the air through to keep the sound in the cockpit reasonable.

Too hot here in the Carolinas,
Dale

[David M]

You said you want hard data but no opinions. Your hard data will be different from others hard data anyway since all boats are different. So only wanting hard data may be limiting your responses.

I know how to cool engine spaces, but that is not what you want.

[billknny]

Originally Posted by DaleM

I have a Morgan 40 ketch with a Westerbeke 55c engine (55hp). I sound insulated it with a layer of Hardi board cement board, a layer of Green Glue and another layer of cement board. It is completely sealed off from the cabin and has an air intake opening leading to the cockpit lockers that are vented. I used cement board due to lack of space, using mass/ rubber / mass.

The engine is very loud without sound insulation. It runs at 180F. I have ran it 500 hours like this but mostly during the winter. I ran it for 2 hours yesterday, outside temp was 90F. I opened the engine compartment several minutes after stopping, it would have gotten hotter. The walls were 125F, transmission 150F, engine between 150F and 180F. The transmission has a bolted on cooler.

Should I be concerned? The engine pulls around 70cfm when running. The biggest engine fan that has a reasonable price is 250cfm and it may make no difference. It would be pulling 90F air through an engine room that's radiating heat at 180.

Has anyone installed a fan that has made a measurable temp difference? I would like to hear actual before and after temps not opinions. If I install a fan then I will need to make baffle boxes to feed the air through to keep the sound in the cockpit reasonable.

Too hot here in the Carolinas,
Dale

There are good reasons to use fans other than just lowering the bulk air temperature of the engine room. Primarily to deliver cool(er) air to at least the general vicinity of the engine air intake. The engine really doesn't care about living in a hot room, what it DOES care about is having to breath really hot air. The hotter the air, the less dense, and the less oxygen there is sucked in on each piston stroke, and the less power the engine makes. Sucking hot air from an overheated engine room is kind of a negative turbo charger!

Having a fan pushing outside air into the engine space near the engine intake can make a significant difference in engine performance under hot conditions. Of course you now need a way for the excess hot air to escape...

If you put in a 70CFM fan you would make almost no difference in overall engine room temperature, since the engine is already sucking that much air through on its own.

If you rig the fan to run when the ignition is on, then the hottest the engine space will get is shortly after being shut down as the hot engine block equilibrates with the surrounding space. Not a problem for the engine, might be for the boat cabin in a hot climate. That heat EVENTUALLY has to go somewhere...

If you have electronic devices that live in the engine room, then check their high temperature specifications to be sure you aren't cooking them.

And for heavens sake, keep any batteries out of there!

[DaleM]

I was bit hot and grumpy when I wrote the first post. I did a search before posting and found 428 threads with the words engine room temp, most of them about batteries.

In the relevant ones I could find there was no data. No one had a before and after measurement of the engine room temp. I, and I think many people, know a hot engine room is not good but the consensus was that most people ignored the issue.

I'm hoping someone did temperature measurements and could tell me if it is worth the trouble. Dale

[a64pilot]

A lot of manufacturers fit bilge blowers that run when the engine is running.
Likely they did it for a reason, I’m keeping mine operational.

[evm1024]

I use a Jabsco 4" flex mount blower in my engine room. THe part number is 35770 I think I recall.

This 250 cfm blower sucks the hot air out of the ending room like crazy and lowered the engine room temp a lot. I have a huge engine room so that is saying a lot.

If you were to put this in a small engine room it would quickly bring the engine room temp down close to ambient.

If you want to feed cool, outside air to your engines intake you will want to use a blower like this to exhaust the engine room and then run a duct from outside the engine room over near the engine intake. The blower will cause cool air to enter near the engine.

If you use a blower to bring outside air into the engine room then you will end up with smelly, hot engine room air leaking into your cabin and stinking up the boat.

[GordMay]

According to one self-styled expert:
The maximum temperature of the engine room should never exceed 140 degrees F, within 3/4" of any electrical equipment (ie: Alternator), and should never exceed 115 deg. F anywhere in the engine compartment.
A common rule of thumb holds that decreasing air intake temperature by 10 degrees F will increase horsepower and torque by 1%.
From ➥ http://www.cruisersforum.com/forums/...t-37561-2.html

See also, a “professional” opinion ➥ https://www.proboat.com/2015/06/venting-the-engineroom/

[Pelagic]

When working out design criteria for cooling engine room, it is all about Air Changes per hour.

But you haven't given us the volume of the engine compartment so its hard to calculate the number of air changes for an unknown volume.

We normally design for 95°F ambient temperature in the room at max continuous rpm, so it sounds like your temp is high.

To improve this, you need to increase air changes, which means two fans....
One in/One out

But their is an additional trick.

The Intake Blower should be ducted under the engine to the cooler bilges where it can be consumed by engine.

The Exhaust Blower is only ducted to the ceiling. Where it removes the hottest air and enhances the cooler air circulation.....Hope this helps!

[GordMay]

Caterpillar specifies the maximum engine room temperature as 120°F
Note on Page 3 ➥ http://s7d2.scene7.com/is/content/Ca...13-53120-44971

I believe that ABYC recommends a maximum engine room temperature of 50 degrees C (122°F).

[NYSail]

Hot engine compartment = bad engine performance and horrible charging performance. Alt will shut down quickly due to heat. And as mentioned any electronics or wires in there will suffer. My engine compartment has an electric exhaust with 2 intakes. Compartment stays cool enough. My batteries are in there and the hottest I ever saw them was 80f but that was when they were taking a bulk charge.
Why cement board? That stuff will retain the heat for long periods. Lead lined foam that is designed for engine room noise suppression is what I have and mine stays relatively quiet.

Good luck
Greg

[Scrimshaw4]

I have a 2 position switch near my engine panel for the engine compartment blower. Ignition on and continuous. On hot summer days I'll switch over to continuous for a little while to cool the engine compartment.

[a64pilot]

Originally Posted by Scrimshaw4

I have a 2 position switch near my engine panel for the engine compartment blower. Ignition on and continuous. On hot summer days I'll switch over to continuous for a little while to cool the engine compartment.

I’m considering that myself, but to keep the engine from inside of the boat after we shut down and are at anchor.
A few hundred lbs of metal at 180 or so has to heat the inside of the boat if not ventilated

[David M]

Cummins Marine requires that the engine room air not rise above the ambient outside air temperature by a specific amount. I do not remember the exact amount but it was not a whole lot. I am going to guess 20-30 degrees Fahrenheit.

On some boats a forced draft blower is required and on some boats a chimney effect is sufficient.

[Scrimshaw4]

I run my blower after shutdown in the summer to help dissipate heat buildup inside the boat.

[GordMay]

Originally Posted by David M

Cummins Marine requires that the engine room air not rise above the ambient outside air temperature by a specific amount. I do not remember the exact amount but it was not a whole lot. I am going to guess 20-30 degrees Fahrenheit ...

Good guess!

“... Ideally, the delta t, which should be measured at the engine or generator air inlet or filter, and at the louver where air is drawn into the engine room from the deck, should not exceed 30°F/16°C. (This varies among manufacturers so, for instance, while Cummins and John Deere specify 30°F, Caterpillar and ISO 8861 call for a maximum delta t of 22.5°F/13°C.)
Maximum overall air inlet temperature should not exceed 122°F/50°C. (Again, it varies by manufacturer: Cummins specifies an absolute maximum of 150°F/65°C.)...”

From ➥ https://www.proboat.com/2015/06/venting-the-engineroom/