Time to replace engine rear seal?

[jimp1234]

I have a Perkins 4-154 that was on the boat when I bought her 5 years old. It only has about 1200 hours, and I've replaced injectors, hoses, etc. and it generally runs pretty well. I've started seeing more oil on the oil diapers, and I'm pretty sure I've got a leaking rear seal. I'm adding 1/2 - 3/4 qts. of oil for every 100 hours running time. Some of the "diesel guys" I've spoken to have said that these old engines with "rope" rear seals will always leak a bit so just keeping adding oil. And on my boat this looks to be a tough replacement job. So replace the seal soon, or can I wait a while?

[Scubaseas]

It'll leak less as the oil gets lower if that helps. 1/2 qt. low makes for less leak on most engines. It'll leak faster if you keep it full but yes, two piece rope seals will leak, especially on a three main bearing motor. They do make a two piece rubber lip seal that seems to work OK but I don't know the longevity. These won't work if you have sipping (small grooves) on the crank. 1/2 qt every 100 hours is pretty normal for a 4-108. If you can live with the leak and cleaning the spilled oil up, you can probably run it that way for a several thousand hours. You could fix it with a new seal (without removing the crankshaft, it's on a plate that bolts to the block) and have it leak in three years or three months.

Some people have had luck using Lucas Leak Stop to slow the leak down but you're never going to stop it.

It will not fail catastrophically. It may slowly leak a bit more and more. You can buy a lot of oil for what it would cost to fix it.

[Lepke]

The is a kit with modern materials that replace the rope seal. New seal lasts a long time.

$30 at https://www.parts4engines.com/
$120 at https://www.foleyengines.com/