Oil dipstick tube replacement 1991 5.7

[drodkey]

Went down to the boat this morning, and found oil in my bilge. Last weekend we put 75 miles on her and didn't notice any issues with oil pressure. Utilizing my camera phone on video I was able to look at the oil pan and drain plug and found no leaks. Then I noticed the dipstick was sticking through the tube down into the bilge. The dipstick tube has corroded and appears this is the source of my oil in the bilge.

The group was very helpful when I recently had to replace the hard fuel lines last month. I'm wondering if there are any tips or cautions to be aware of when replacing the tube. It appears the easiest way to do this will be to remove the exhaust manifold. Any advice on replacing the tube or pulling the exhaust manifolds / risers would is greatly appreciated. Engine is a 1991 5.7 Mercruiser sn 0D603540.

Thanks,
Dave

 

[kenny nunez]

Where goes the tube connect to the engine? Oil pan or into the side of the block?

 

[drodkey]

Side of the block I believe. At least looking at the parts diagram that's what it looks like. I'll have to walk down and double check.

 

[kenny nunez]

If there is not enough of the tube sticking out of the block pack the tube with some grease then either a 5/16” OR 3/8” fine thread tap to thread the inside of the tube so that a stud can be screwed in to extract the tube using some spacers. If there is some sticking out then insert a bolt that fits in the tube to keep from crushing the tube then grab it with some vice grips to work it out.

 

[drodkey]

The corrosion is actually at the other end of the tube. Closer to the dipstick it’s self. I’m at a lose though. Last ran the motor on Monday. Went down Thursday to clean up some leftover deck mess from the weekend. Bilge kicked on from the washing and was clear water. Open today and oil covering the water in the bilge. Dipstick shows down a quart. Only issues I’ve been able to locate is the corrosion of the dipstick tube, however since the motor hasn’t run that doesn’t make since as its above the oil pan. Using the video camera on my phone I’ve run the bolts of the oil pan with no leaks. Drain plug is clean. Only issue we’ve recently addressed was replacing the belts. Seem pretty tight..

 

[sms986]

I just got done building a 5.7 for my boat. I believe yours has a 1 piece rear main seal as well, and you may have a cork gasket that sits between the dust shield and flywheel housing. The pan has a few small bolts that hold it on and are very difficult to get to, but if you have oil dripping into your bilge, you should be able to run your fingers around the bottom of that plate and feel for oil. That is a good place to check.

 

[achris]

Even if the dipstick tube corroded off right at the block, the oil level in the engine doesn't come that high when the engine's not running. For oil to leak out, and in that quantity, you must have a hole in the sump (oil pan) or a loose sump plug...

Given the engine is 27 years old, and the boat lives in the water (I'm assuming salt), then it's well know that any salt water, and that can just be from salty air condensing on the sides of the sump, will collect at the lowest point, that's the little dip just under the sump plug. Over time, the pressed tin sump will corrode right at that spot... And eventually it'll start leaking oil... The fact that your dipstick tube has corroded away is a good indicator that plenty of corrosion is going on 'down there'....

I have fixed a LOT of corroded sumps like this... All I do it pull the engine, get the sump off and weld a small plate over the hole, then have the sump hot-dip galvanized, before priming and painting it...

Chris..........