TOPIC: Chrysler Inboard Oil Drain Mod

The Chrysler LM318 in my '73 Century Resorter has the typical cast aluminum oil pan that Chrysler installed on all their inboard engines.. Chrysler doesn't extend the dipstick tube to the bottom of the pan like other marinizers.. They only install a drain plug in the front of the oil pan or you have to use the other dipstick tube hole to insert a tube to pump out the oil in order to change it..

The steep shaft angle in the Century pretty much made the drain plug useless as it would only drain out about 1 1/2 - 2 quarts, a cast in baffle a few inches behind the drain plug prevented inserting a tube for a pump.. Pulling the plug from the other dipstick tube hole on the other side of the pan allowed you to stick a piece of tubing down to the bottom of the pan just aft of the middle, this still left about a couple of quarts of old oil in the pan..

I decided to address this problem while I had the engine pulled out of the boat and torn down to replace all it's leaky gaskets & seals.. After a couple of rum & cokes and a cigar I came up with a solution..

Here's the pan with the oil pump & pickup sitting in it's normal position.. There's still a "bathtub ring" in the pan that shows where the normal oil level is..

100_2702 by cc_john67 , on Flickr

Here's the "drain" plug in the front of the pan..

100_2704 by cc_john67 , on Flickr

My solution to the problem of draining ALL the oil from the pan during oil changes begins with bending up a piece of 3/8" copper tubing.. I then used an extended length 3/8" drill bit to drill a hole thru the bottom of the cast in baffle behind the drain plug..

100_2705 by cc_john67 , on Flickr

100_2706 by cc_john67 , on Flickr

Here's the tube installed in the pan for a test to see how it will clear the oil pump pickup.. I don't think there will be any problems getting ALL the oil out of the pan during an oil change..

100_2707 by cc_john67 , on Flickr

100_2708 by cc_john67 , on Flickr

Then I drilled out the back of the drain plug bushing and tapped it for 1/4" pipe thread, this is to accept a 1/4" MPT x 3/8" compression adapter to secure the tubing.. Here's the tube on it's final install..

100_2711 by cc_john67 , on Flickr

100_2712 by cc_john67 , on Flickr

A 1/4" street ell is installed in the front of the bushing, I'll have a 3/8" hydraulic hose made up with 1/4" MPT ends that will connect to the elbow and the other end secured up high on the engine for easy access and capped with a threaded cap..

100_2713 by cc_john67 , on Flickr

That'll work.

63 Sabre wrote:

That'll work.

I'm hoping so..

The amount of leftover sludge (3/8" deep at the back of the pan) I cleaned out of the pan after removal was staggering.. I also spent some time with a die grinder cleaning up leftover casting flash that was impeding the free flow of oil around the ends of the baffles..

What I usually do when changing oil on my cars is to do it when the engine is hot. This gets that waxy sludge loosened up otherwise it just stays on the bottom of the pan like you found. Elbow grease to remove the oil. She'll be a new engine when you're done.
Keep up the good work.

63 Sabre wrote:

What I usually do when changing oil on my cars is to do it when the engine is hot. This gets that waxy sludge loosened up otherwise it just stays on the bottom of the pan like you found. Elbow grease to remove the oil. She'll be a new engine when you're done.
Keep up the good work.

Cal,

You're preaching to the Choir, I have the same habit as you..

The problem with most inboards is they run so cold because of the 140* thermostats that are usually installed in them, coupled with the fact that you can't get them to warm up enough when on the trailer running on a garden hose.. When I was keeping my Chris Craft in a slip, it was easy enough to take it out for a short run to really warm up the oil under load before an oil change.. When I tore that engine down here a few years ago to replace a rusted out block, the oil pan was spotless inside..

The sludge buildup in the Chrysler's pan was more than likely the result of years of oil changes that usually left a couple or more quarts (capacity is 6-7 qts. w/filter) of the old oil behind because of having only two marginally effective drain ports coupled with a steeper than normal shaft angle that kept oil from easily reaching those ports..