Mercruiser inline 6

[Sangster21]

I am putting some feelers out to see what is available. I have a Mercruiser 250 cu in I6, which I have had recently rebuilt, but have had nothing but issues with it. I have some more checks to do, but I have a feeling I am in need of a new block. Does anyone have or know of a MC 165 that needs a new home?
Thanks,
Alan

 

[MOBY DICK]

Whats the problem ? Water/antifreeze in the oil ?

 

[Sangster21]

The problem is coolant loss and significant quantities of steam venting from the valve cover and from oil dip stick. There is some water in oil, but no signs of pressurizing the coolant system. I have pressure tested my 1 year old manifold, replaced riser gaskets, had my cyl head checked for cracks and pressure tested, block and head are both flat. Cylinder 1 shows as steam cleaned, somehow coolant is getting in there and it appears not to be past the head gasket. It seems only option at this point is to remove and disassemble to find the cause.

 

[Goathorns]

It sounds like a cracked cylinder head, cracked block, or bad manifold. Something is letting the water/coolant in.
It must be difficult and awkward to pressure test the manifold and/or the cylinder head. I'm surprised to hear you had it done. Did the machine shop say anything about the parts when they had them?
good luck with it.

 

[Sangster21]

The manifold was not too difficult to pressure test, I blocked off one end of the manifold, rigged a tire valve in the other end and pressured the coolant passage with compressed air. I left the elbow with block off plates on. I made a block off plate for the carb mounting surface out of acrylic and sealing it up with some silicone. Filled the intake with water and looked for any bubbles. I am not entirely sure how the machine shop tested the cylinder head, but they assure me it is good.

 

[Goathorns]

Have you been taking it out lately and then something changed or has it been this way since putting it together? Is the thermostat able to regulate the heat? what is the running temp. and coolant level? A little bit of water in the oil will evaporate off through the oil filler neck and dipstick holes. only an hour or so of running will clear that up, if it is not continually coming in.
If you have been backing up or slowing down suddenly you could get some water to go up the exhaust pipe. It would have to go past the water stopper valve in the lower exhaust pipe.
If that is not the case, then it is back to suspecting your manifold. You may have to take it back to them and complain. testing yout manifold cold is not good enough. good luck.

 

[Sangster21]

After having the head pressure tested, I re installed with new gasket and replaced the old original head bolts with ARP studs. Even idling on the muffs I started to get steamy blowby appearing at crankcase breather. Took it for a sea trial again as the problem gets worse with RPM. Off we go, cruising at 3000rpm ans steam is pumping out of the crankcase breather. Back to the dock to pull the carb off so we could swab the intake manifold to see if coolant was somehow present. Nada. Water is getting in somehow. Temp remains steady throughout test, I have both a new leg impellor and in block water pump. I looked for any sign of water intrusion in exhaust runners of manifold but saw no sign. The most likely cyl to have that issue is #6 as it is closest to the back, but cyl #1 is the one with obvious signs of steam cleaning. When I pulled the head this morning the piston was near TDC and did have a tiny bit of coolant on top of cylinder. I barred the crank to inspect cyl #1 again and no visual indication of breach. I am at this point somewhat suspicious of the thread repair to one of the front head bolts near the water pump. I have noted marking on the head gasket that to me indicates some movement when torqing the head. Fortunately I do have what appears to be a good block to bring down to the machine shop when I drop off the block for inspection.

 

[Goathorns]

they must be able to X-ray it or something like that.? they must have noticed it at the time. Did they mention it?

 

[Sangster21]

They installed the thread repair when they did the machining for the rebuild, claimed it is not at all uncommon for these blocks to have a crack at this location.

 

[Sangster21]

I have pulled the engine and taken it apart. Close inspection has revealed a small crack about 3" down in cylinder #1. I took it into the machine shop this morning, he verified that there was indeed a crack. He says they can install a sleeve and it should be good to go. Unless they have an issue getting gaskets, it should be ready for pickup on Saturday and I can re install the engine.