View Full Version : 50L Mercruiser Engine Troubles

Nick Horner
04-30-2006, 09:10 PM
"I just bought a 1994 Bayliner with a 5.0L Mercruiser engine. I took it for a test drive and everything ran great. After getting it home I took it to a mechanic who discovered that I had two cracked manifolds (the ones on the sides of the engine) but said that the block looked good. Prior to getting anything serviced the engine fired up and ran smoothly. Once I got it back it really struggled to start and would die when idling. I figured it was the old gas in the tank and went out on the lake. It ran smoothly once I got the RPMs up but still struggled at idle. The major problems stared when I tried to restart the engine while on the lake. It started making a hard clunking (metal on metal)noise when turning over. The first thing I checked was the oil. It was filled to the proper level and I didn't notice any discoloring. I managed to get it started and it seemed to run fine once started. After driving back to the marina we pulled it off the water to try to diagnose the problem. Now the oil is milky and there is a tan oily mess on the carb. This sounds very similar to the post titled "tan fluid coming out of carb." Could the mecahnics have put in a bad gasket that caused this? Like I said, it ran great until they worked on it. Any advice would be appreciated."

05-01-2006, 08:45 AM
"Sounds like you may have blown a head gasket. Do a compression check, and DON'T run it! If I'm right you'll fire-score the block, ruining it.


Nick Horner
05-01-2006, 12:08 PM
My mechanic is telling me that he thinks the exhaust baffles could have been stuck open and let water flood back in if the boat was stopped suddenly. However he said that the only way this could have happened is by overheating. He just replaced the water pump kit and said that it was functional but should be replaced while he had it open. He also agreed that the oil was clean when he changed it. The boat had been run several times between de-winterizing and him changing the oil. Wouldn't a cracked block have shown signs before now?

05-01-2006, 02:13 PM
"Am I reading this correctly?
You have two cracked exhaust manifolds, and you think you have bad gas... And you went out on the lake? The first thing you need to fix is your judgement... 'nough said.
As far as the cracked maifolds go... there's more than one possibility there, but the most likely cause is improper winter layup causing freeze cracking. How could you be sure those were the only cracks? Another common place for cracking is the engine block water jacket into the lifter/push rod gallery.
You've got significant work and expense ahead of you. Your mechanic's story doesn't seem to make much sense... almost sounds like he's trying to cover his tracks. If you're in over your head take it somewhere else.... and buy a book. Learn the systems enough to at least understand how things work... for two reasons:
1) You'll know when a 'mechanic' is jerking you off.
2) Your life may depend on it, and you are ultimately responsible for the quality of work done on your vessel... even if you're not the one turning the wrenches."

Nick Horner
05-01-2006, 06:05 PM
"Apparently my posts were not clear. I took the boat on the water during a test drive. Then it was discovered that there were two cracked manifolds but everything else looked good. I had the manifolds replaced, then went out on the lake. The boat was starting much rougher after the repairs were done but I thought it could have been the old gas in the system that just needed to be flushed out. The hydro locking started after running around on the lake for a while. Since my last post the mechanic has diagnosed it as bad exhaust flapper/baffle on the right side. He claims that the rubber was completely gone off the stainless flapper. I could understand water running in once after driving fast and suddenly stopping causing a wave to hit the back of the boat but it happened again after I idled into the marina and coasted into the dock (gradually slowing). The good news is that he drained it out and changed the oil and now it fires up and there seems to be no other damage. The bad news is that I am out another $400. I am concerned that he is jerking me around because I told him to stop working on it so I could see the bad part in my boat but he has gone on to fix the problem already. Has anyone ever heard of an exhaust baffle going bad and causing this kind of problem?"

05-01-2006, 08:20 PM
"Rubber exhaust parts usually go bad from bad impellers and old age. If there's no cooling water going through the system, there's nothing to cool the exhaust gases and anything made of rubber goes away."

05-02-2006, 07:18 AM
"OK, I feel better. Sorry if I sounded like I was standing on my soap box, thumping the Bible.
I love helping people, but "You can't fix stupid."
Glad to hear your not in that category.

I'm not buying the bad exhaust flapper theory unless you know you did in fact back down hard into your own wake and stall the engine.... as long as the engine was running when you did that, the exhaust pressure would not have allowed water back into the engine through the exhaust. (Ever drive a car through deep water? Same deal.)
My recommendation is, before you leave the mechanic's lot, run the engine on the rabbit ears, with him watching, for a long time... 30 minutes to an hour minimum. Then check the condition of the oil."

05-03-2006, 10:15 AM
"Thanks for all the advice. I ended up splitting the cost of the repairs with my mechanic because the baffle was bad but he showed me the gasket for the manifold and I pointed out two big holes where water would have been pushing into the exhaust (looked like he hadn't replaced the gasket when the manifold was replaced). Neither one of us could prove that one thing for sure caused the problem and the other did not so we decided to split the difference. The engine is back to running smoothly now with no additional damage done. I was happy to get out of there for $200, going in I thought I needed a new engine. Hopefully I have better luck this time out."