Replacing engine compartment insulation - but is it soundproofing?

July 24, 2011
original foam and foil insulation
The original foam and foil insulation

Distintegrating old foam and foil engine compartment insulation – long past time to replace this, but was anything actually going to help with the noise of the old diesel tractor engine?

Trolling through forums last year turned up quite a bit of info and different products, AND lowered any expectations I harbored about a significant decrease in the noise from the diesel. But the old stuff had to go so I might as well replace it with something…

Something with lead was supposed to be the best for a sound barrier, but on the 1984 Catalina 36 I have to lift the engine compartment lid out of a bracket to access the engine and adding more weight didn’t seem too practical. The price of some products didn’t fit my cost to benefit ratio. What did fit was the SPM product from – $105 (plus about $30 for shipping) for a pack of 12 tiles and it seemed simple to install.

all the old stuff removed
Engine compartment ready for new insulation

Taking off the old stuff – simple! Unscrew the retaining screws and peel off. Next step, mineral oil to remove the remaining glue, then a little bit of light sanding – what the heck? Am I refinishing this thing or sticking glue tiles on it? Next step, analyze how best to put the tiles on there with minimum cutting.

new insulation
Engine compartment insulation soundproofing tiles

Peel and stick – the glue is really sticky, you want to get the tile in the right place the first time. You can cut the tiles with a utility knife, would probably be best to use something with a blade long enough to cut all the way through on one pass. I cut it in two passes with my small blade and put the factory cut edges on the outside edges of the compartment to eliminate any flaking from jagged edges of the cut foam.

Tip: Don't put the tiles flush with the sole - that stiff edge will really scratch your nice finish when you slide the engine compartment cover off the engine!

all the old stuff removed
Engine compartment insulation - a peek inside the cover


The alternator bracket rubbed through the old insulation, that was going to be true with the new 1 inch thick insulation when the cover was completely on.

But is it soundproof?

NO, it is not soundproof. With the diesel idling it IS quieter standing in the galley next to it, but in the cockpit with the diesel full throttle, thrumming along at sea – that noisy vibration sounds the same to me. Keep those noise canceling headphones handy for a long motoring trip!


Universal M25 Diesel

Heat Exchanger

Engine Compartment Insulation / Soundproofing

Anchor Locker





Bimini for the Boat



Edson Pedestal Controls