Hi everyone,
I rebuilt my two Mercruisers 7.4 MPI Mark VI engines a month ago, they are both closed cooling system including manifold (except the elbows), since rebuilt I noticed that the port engine was always showing fine bubbles coming out the exhaust through the sterndrive while the starboard engine show no bubbles whatsoever (the way it should be). apart from the fine bubbles it also has a minor missfire only at iddle but ran fine.
This weekend while doing maintanance, I notice water in the oil stick (about 2 qt got out of the pan) I only went out for a 15 minutes ride at no more than 2,000 rpm. I changed the oil and spark plugs and ran the engine at 1300 rpm (in neutral) for 10 minute and no signs of water following the mercruiser guidelines to save the engine for water intrusion.
Now, I have had my fair share of water intrusion issues over the years and I have managed to find the causes, however, this time is different as the water in the oil pan is RAW WATER, which means that is not coming from internal parts. Exhaust shutter flappers are new as well.
I pulled the spark plugs and all cylinders were dry, however, I test I do every time is to pull the spark plugs and lick the electrode, then cylinder 5 & 7 were salty but completly dry all other spark plugs were not salty and dry as well.
Did pressure test and all cylinders fired up to 150 PSI, now, the million dollar question is how raw water got to the oil pan!, I know that a non working exhaust valve can draw raw water even a spark plug, particularly on sterndrives, however, theory says that if there is a problem with a valve, cylinder pressure should go down and this is not the case.
As far as I know the other thing I need to check is the oil intercooler for internal leeks, apart from that am completely baffled!
Any suggestions will be very much appreciated.
I rebuilt my two Mercruisers 7.4 MPI Mark VI engines a month ago, they are both closed cooling system including manifold (except the elbows), since rebuilt I noticed that the port engine was always showing fine bubbles coming out the exhaust through the sterndrive while the starboard engine show no bubbles whatsoever (the way it should be). apart from the fine bubbles it also has a minor missfire only at iddle but ran fine.
This weekend while doing maintanance, I notice water in the oil stick (about 2 qt got out of the pan) I only went out for a 15 minutes ride at no more than 2,000 rpm. I changed the oil and spark plugs and ran the engine at 1300 rpm (in neutral) for 10 minute and no signs of water following the mercruiser guidelines to save the engine for water intrusion.
Now, I have had my fair share of water intrusion issues over the years and I have managed to find the causes, however, this time is different as the water in the oil pan is RAW WATER, which means that is not coming from internal parts. Exhaust shutter flappers are new as well.
I pulled the spark plugs and all cylinders were dry, however, I test I do every time is to pull the spark plugs and lick the electrode, then cylinder 5 & 7 were salty but completly dry all other spark plugs were not salty and dry as well.
Did pressure test and all cylinders fired up to 150 PSI, now, the million dollar question is how raw water got to the oil pan!, I know that a non working exhaust valve can draw raw water even a spark plug, particularly on sterndrives, however, theory says that if there is a problem with a valve, cylinder pressure should go down and this is not the case.
As far as I know the other thing I need to check is the oil intercooler for internal leeks, apart from that am completely baffled!
Any suggestions will be very much appreciated.
