What is this hole in the block?

[MelLandry]

After my last trip I came home, unhooked the boat, and jacked the front of the trailer up.

I went in my driveway this evening to find the ground full of oil (which drained from the bilge).

I began the daunting task of removing the back seat to get a clear look at the engine (a 2bbl 350). I added oil and started her back up with flash light in hand. Looked all around at the suspected sources of the leak. I didn't see much.

I did find a hole in the block on the starboard side of the boat. I'm hoping you all might clue me in on what it is and if there should be something in it. There seemed to be a light mist coming from the hole but I was unable to determine if it was oil.

In the pictures the hole is surrounded by some orange substance...

 

[Don S]

Re: What is this hole in the block?

It's for a block mounted dipstick tube. Most marine engines now have the dipstick tube mounted to the bottom of the oil pan and that hole is just plugged. I usually seal a 3/8" bolt into the hole, using the same ultra black sealer as used on the intake. Has worked for many years.

 

[f_inscreenname]

Re: What is this hole in the block?

It's for a block mounted dipstick tube. Most marine engines have the dipstick tube mounted to the bottom of the oil pan.

Don beat me to it. I'm thinking that should be closed off.

 

[Don S]

Re: What is this hole in the block?

Don beat me to it. I'm thinking that should be closed off.

That plastic plug was only meant to keep the dirt out till the dipstick was installed. Should never have been left in there.

 

[MelLandry]

Re: What is this hole in the block?

Thanks guys.

Would that plug missing cause nearly the entire pan to empty? There was a light mist at idle, but I would guess more would be ejected at higher RPMs...

 

[Don S]

Re: What is this hole in the block?

Sure would, over time. Plug it up and try it again.
it's also a good practice to check your engine compartment Before you start the engine. During the day to make sure things are going ok, and at the end of the day to see that things are as they should be. Lots of people never open the engine cover and assume everything is the same as it was last time. Lots of boats sink for that reason.

 

[MelLandry]

Re: What is this hole in the block?

I normally do all of the above (and randomly during the week to remove moisture, etc), but on the last trip pickup was very late. After past incidents, I pay very close attention to my gauges as well. I'm just glad I was able to diagnose (hopefully) in short time. Now it'll take me another 3 hours to get the rear bench back in...

 

[f_inscreenname]

Re: What is this hole in the block?

At speed I could see that dumping a lot of oil out. Plug it up and go.

 

[Don S]

Re: What is this hole in the block?

Now it'll take me another 3 hours to get the rear bench back in...

Isn't it great how the manufactures make it very easy to do preventive, or for that matter, any kind of maintenance on a boats mechanical parts.
Don't you really want to own a boat that takes 12 hours to R&R the engine just so you can change the raw water pump impeller every other year?

 

[captk]

Re: What is this hole in the block?

Just an observation. Those are after market manifolds, and an old style trim pump. if someone switched from aft riser to center riser manifolds the dip stick may not have worked. Also merc used a dipstick oil suck at that time not a oil pan screw type. As for spending 4 hours removing seats and panels and then hearing how "that cant be I bought a XXX boat and they would not do that they are great boat builders". I got to the point that I would tell them" I did not design,build or most importantly, I did not buy this boat. Call that builder and complain. This is why I am no longer doing this kind of work.

 

[f_inscreenname]

Re: What is this hole in the block?

Isn't it great how the manufactures make it very easy to do preventive, or for that matter, any kind of maintenance on a boats mechanical parts.
Don't you really want to own a boat that takes 12 hours to R&R the engine just so you can change the raw water pump impeller every other year?

As I get older I am learning to appreciate the motor access I have more and more. I don't think I could hang upside down in a motor box for a hour putting a starter on anymore.

 

[captk]

Re: What is this hole in the block?

NO pics but does anyone remember the 23' or 25' formulas with twin big blocks. 1/2" between manifolds. mid to late 70's. ahh the good old days

 

[MelLandry]

Re: What is this hole in the block?

Just an observation. Those are after market manifolds, and an old style trim pump. if someone switched from aft riser to center riser manifolds the dip stick may not have worked. Also merc used a dipstick oil suck at that time not a oil pan screw type. As for spending 4 hours removing seats and panels and then hearing how "that cant be I bought a XXX boat and they would not do that they are great boat builders". I got to the point that I would tell them" I did not design,build or most importantly, I did not buy this boat. Call that builder and complain. This is why I am no longer doing this kind of work.

I had a shop do a short block replacement, and changed the manifolds to center risers at the same time. The dip stick was never in that location (before or after). it's actually on the other side of the motor.

Can you explain the "dipstick oil suck" at little more... I haven't a clue what that means. Will this effect how I plug the hole? Or are you just refering to the way the oil is removed from the pan when changed?

And since your noticed the trim pump... does anyone have a diagram or more info on that trim system. Maybe even a name for it so I can look it up. I'm sure it could use a little prevenative maintenance.

 

[MelLandry]

Re: What is this hole in the block?

It's for a block mounted dipstick tube. Most marine engines now have the dipstick tube mounted to the bottom of the oil pan and that hole is just plugged. I usually seal a 3/8" bolt into the hole, using the same ultra black sealer as used on the intake. Has worked for many years.

Two more questions...

What type of threads on that 3/8"? Normal, fine?

I assume I need to remove the plastic residue around the hold before I'll be able to install the bolt, correct? I also assume I need to be very careful not to drop said residue into the block, yes?

I know these are elementary questions, and I could probably proceed and figure this all out on my own... but why not ask and remove all doubt? Thanks for all your help.

 

[Capt Ken]

Re: What is this hole in the block?

There is no threads, just a smooth hole. I doubt if much if any oil blew out that hole. You probably saw blowby coming out the hole the same as the breather vents on the valve covers. Bet you find a rust hole in the oil pan.

 

[captk]

Re: What is this hole in the block?

The oil suck dipstick I refer to is one with the gardenhose fitting on it. the tube goes to the bottom of the oil pan so you can remove the oil more easily. The 79 260 I just looked at has a place for that hole on the stbd side but is not bored. the newer engines have the dipstick on the stbd side. Could be a difference between 1 and 2 piece rear seals and Gm's redesgns.

 

[MelLandry]

Re: What is this hole in the block?

Thanks for all the help.

After I initially noticed the low oil, I added oil and started the boat on muffs just to make sure no additional damage had been done. Over the next couple of days I didn't lose another drop (so I assume it's not a hole in the pan). I inserted a 3/8" bolt with Black Majic, did a complete oil change and fired it up on muffs. Everything looks good.

Getting to the hole was interestin. My hand certainly wasn't going to fit that far in. I used a 4-pronged "grabber" to guide the bolt in and set it. Couldn't have done it any other way.

I'll get her on the water in the next couple days and do a complete test.

While everything was pulled apart, I remounted the fuel filter, added fluid to the trim unit, and addressed a auto-bildge float issue.

Thanks again for all your help. I'll update y'all when I get it on the water.

 

[MelLandry]

Re: What is this hole in the block?

Boat ran like a champ yesterday. Not a drop of oil in the bildge.

Also found my trim fluid leak. Easy replacement of a hose on the outdrive... as soon as I figure out the part number for the hose.

Thanks for all the help. This would have cost me a chunk of $$ to diagnose and fix if I had to bring it to the shop.

 

[bekosh]

Re: What is this hole in the block?

As I get older I am learning to appreciate the motor access I have more and more. I don't think I could hang upside down in a motor box for a hour putting a starter on anymore.

f_in, I hate you.
I have a 7.4l in my boat, but the front of the bilge is only about 1" away from the front of the motor, I have about 3-4" from the storage bins on each side and when the bench seat is in place there's 2" between it and all the pullies. Simply changing the alternator this spring, took me almost 3 hours.
And don't even get me started about the bilge pump that's mounted right under the oil pan.

 

[superpop]

Re: What is this hole in the block?

That is indeed a dip stick hole that is not used in marine apps. I had the same thing with my 4.3L gm Small Block. I just hammered in a piece of dowel and it has been good for several years. You can lose a ton of oil out of this hole if it is not plugged.