ScarabMike

Sorry for the long post, but I'm new to the performance boat arena. My last boat was a 26 foot cruiser.

I just purchased 1 1997 31' Scarab with twin 502 Mag MPI's. I took it out for a test run yesterday and here are the results.

Once I launched the boat, both motors started perfectly and ran very smooth. I ran at idle or just above for about 15-20 minutes and all gauges looked good on both motors. Once I came on plane, the boat seemed to run nicely. I was running about 5000 RPMs on each engine with just a tiny bit of throttle left. After running for about 5-10 minutes, the starboard engine alarm sounded. At first, I thought that I may have been overheating because it was at a temp of about 180. so I shut it down right away. Port engine was running fine.

I returned home at idle with 1 motor while the other cooled. I immediately checked the raw water pump impeller and it was fine (I just installed it last week). I also replaced the thermostat as a precaution. When I went to start it again, I had difficulty turning it over. When it did turn over, it idled fine but at about 1200 rpms it had a knock and the rpms would fluctuate from 1200 to about 1500 on their own. As a precaution, I started the port (good) engine. didn't have difficulty turning it over, but it cranked for a long time before starting.

I had to return the boat to the ramp about 3 miles away, so I ran slowly back on both engines. I had a hard time running that boat on just one engine. Is this normal? I coultdn't even think of getting on plane with one engine running, the prop just slipped while hardly even moving the boat if I ran only 1 motor.

I'm getting ready to take it apart now. The oil looks clean, so I don't suspect a cracked block. Due to the age of the boat and the fact that I don't know the maintenance history, I suspect that the problem is with the exhaust risers and/or manifold leaking water into the cylinders. I also think the the port (good) motor is probably having the same problem, but on a much smaller scale. That would explain the hard start. I'll probably replace the risers, manifolds, gaskest, etc on BOTH motors.

My big question is how can I tell if I've done any damage to the motor itself? These motors are still covers under the extended Mercruiser warranty, and my shop tells me that this would be a covered repair. Also, if it caused any other damage, that should be covered as well. I want to make sure that it gets done right before the warranty runs out at the end of this season.

Any feedback would be greatly appreciated.

Audiofn

If you really think you did damage then my first step would be to do a leak down check. From there I would just for a added number to go by do a compresion check. I know basically the same thing but redundency is always good. From there I would pull off the risers and look for any sign of water inside the exhaust. If you have alluminum intakes that is the next place I would look. Good luck.

Jon

ScarabMike

Thanks for the reply. I plan to remove the risers and manifolds today or tomorrow. I'm just concerned that I may have bent a rod, broken a valve or cracked a piston from the water in the cylinder. I don't have any indication of this. I'm just trying to be cautious.

Will these types of problems occur in a pressure check. I have to pull the motor to get to the manifolds, and I don't want to have to do it twice.

LakeRacer

Are these stock manifolds and risers? Or do you have some kind of headers?

Whiteknuckle

Maybe I'm missing something here, but if this is a stock setup with an extended warranty, wouldn't you want to take it to your warranty provider before you start taking things apart? I never mess with anything that is under warranty with the fear that they will say,"its under warranty, but you have already tampered with it." Also did you mean that you ran that boat for 5-10 minutes at 5000 RPM? Wow

David Stotz

I agree with Whiteknuckle. If it's under warranty don't mess with it. Also, why do you think there's water leaking in if it's not in the oil? The last motor I had something similar to this happen there was water in the oil from a crack so small in the head you could barely see it!

blue thunder

If you heard a knock at any rpm, don't touch a thing!!! Probably smashed a bearing under partial hydolock. Warranty claim fast!!

Good Luck,

BT

ScarabMike

Here is an update....

After reading through some other spec sheets, I realized that I was NOT overheating at all. The motor was running at about 175 to 180 degrees! My problem is that the previous owner put the wrong thermostat in the port (working) motor. Since this is the first time that I have ever run 502 Mags, I simply compared the two temps and assumed that I was running hot. I pulled the plugs because that certainly shouldn't affect any warranty claims. There was NO water in any of the cylinders. All plugs looked good. I put them back in and off to the shop it went.

Ass soon as the shop started it up it began to knock hard, even at idle. It sounded to them as though it is a bearing and probably more. The oil pressure looks good at idlem but they seem to think that it dropped very quickly at cruising rpm. If that is true, it wasn't vapor lock that was causing the hard start, but lack of proper lubrication.

I sure am glad that I bought a used performance boat with a factory warranty!

They seem to feel that with the Mercury Extended warranty I am entitled to a short block at the very least. Has anybody had any experience with this type of warranty claim? What can I expect them to offer and can I get anything else. The shop is checking for corrosion to see if he can get a full engine replacement. If that is the case, wouldn't it just be a matter of time for engine #2 to do the same thing?

Thanks for the feedback guys. I've owed a boat for about 15 years. But this is my first performance boat. Now I'm concerned about my other motor doing the same thing.

TomZ

iTrader: (2)

I'm curious about the 5-10 minute 5000 RPM run myself. That might explain why you lost the bearings.

blue thunder

5-10 minutes shouldn't be a problem for a healthy engine. The surveyor that surveyed my scarab said that part of the engine survey would be to run the engine at WOT for 5 minutes. This of course shortens the life of an engine so the more you do it the shorter the expected life of your engine will be. I prefer short burst, say less than 1 minute.

BT