Inline 6 coolant loss and steamy crankcase vent

[Sangster21]

I am going to start a new thread on this issue as I believe I have had some other issues that have been confounding this one. I have a recently rebuilt (bored 0.030" over, new pistons, cam, bearings, head done etc ) chev inline 6 250 cu in mercruiser 165, and am having an issue that is making me pull my hair out. The engine is set up with a heat exchanger, the only raw water is thru the heat exchanger and out thru the exhaust riser.
I am going through coolant and having blowby with a fair bit of steam coming from the crankcase vent. I tasted the liquid that built up on the spark arrestor and it tasted sweet which certainly indicates to me that it is coolant not seawater that is causing it.
When I checked the dipstick there was some signs of milky oil water mix, but only high on the dipstick. The oil when checked shows clear and no contamination by water. The oil fill cap shows signs of oil/water contamination ( milky skudge), but the coolant pressure cap does not, nor does the coolant appear to be contaminated.
My intake manifold is near new, I pressure tested it with block off plates and air, it is not leaking.
I checked my riser for leak ( with solvent) and replaced the block off plate ( old one looked pitted and crappy so I made a nice new one) and installed new graphite gaskets. When I pressure tested the manifold I had the riser in place ..... no leaky.
I have been chasing this issue for quite some time now, I have removed the head and had it checked (magnaflux and pressure) and apparently it is fine. The problem definitely gets worse as engine gets hot. Last time I had it out I ran for about 30 minutes and saw some vapor skudge appearing below the spark arrester....... fished for a bit, then ran home for maybe 40 minutes and it looked like a bit of a steam disaster under the dog house. The problem appears to worsen after a good run.
If I am getting water into the combustion chamber ( this seems like the cause as it shows itself as blow by) I can only deduce it is coming from the manifold or from the cylinder head??!!
What is my next step, pull the head again and have the shop go over it with a fine tooth comb? Haaalp.
Regards,
Alan

 

[998cc]

Alan. When you put the engine together, did you use use sealant on the threads of the various engine bolts, head bolts, etc? Any bolt that is in contact with the water jacket is suspect.

 

[Sangster21]

I certainly did use sealant on the head bolts when I re installed the head. I will look carefully tomorrow when I am back at it again. I am going to make an acrylic block off plate for the carb inlet on the manifold so I can 100% rule out the manifold. I have rigged a pressure test where I can charge the coolant passage in the manifold, fill the intake with water and check for bubbles. I do wonder what bolt holes could result in coolant intrusion into the comb chamber? Another test I thought of is to put a dye pack in the coolant, run it until it steams and then try to trace it that way.

 

[Sangster21]

Took the boat out with a friend today to try to figure out the problem once again. Long and short of it, we notice at higher rpm some coolant leaking from what looks like the head gasket at rear of engine. The engine re builders did a time sert repair of head bolt threads at both the front and back of the block. I will be pulling head tomorrow to have a look. I will check head bolt torque before I dis assemble, but I know the bolts were torqued carefully on re assembly with a 3 pass torque sequence. Hoping I can solve this problem and not have to junk the block.

 

[Sangster21]

Well the head is off and I can see what the problem is...... there is coolant present in cylinder #1. It is not coolant that dripped in as I removed the head, all other cylinders show darkening from combustion, and #1 has a steam cleaned appearance. There is signs of wetness on the valve stem side of the #1 intake passage on the cylinder head. It seems I am off to the machine shop to have cyl. 1 pressure checked. I can't imagine there could be a leak in there that won't result in the call the head is scrap. Can I get a new head, or should I be on the hunt for another core to build?
2nd issue seems distinctly separate to the cyl head issue...... figuring why I have an external coolant leak at the back of the engine. I will check the block surface with straightedge to check for flat.Make sure there is no debris under gasket before I install etc. Nothing seems obvious here.
3rd issue I didn't even mention, but last run I sprung a leak in the rubber exhaust tube that goes from the exhaust elbow down to exhaust pipe that exits transom. When it rains it pours!

 

[xymmot]

I kind of have the same problem. One poster sugguested a crack block because I did not winterize it properly. I saw a u tube video that you might be intersted in that had the oil mix with water to have a milky sludge around.( http://www.youtube.com/watch?v=pyjgzPN4yg0#t=18 ) I have to do a pressure test on the cooling passage and decided it was too much work for me and will let a marine tech figure the problem out, hoping it was the exhaust manifolds that went bad as we check the #2 cylinder as well cause the milky stuff came out the starboard side. Who knows, I am not a machanic and I am too large to get my fat fingers in the engine compartment to pull all these bolts out. But best of luck in sloving your problem.

 

[Sangster21]

I replaced the head, had the manifold surface planed because it was not great and I could see it wasn't sealing well. Not part of the coolant issue, but it certainly won't help it idle of there is a manifold leak. Re installed the head, used head studs..... same steam engine. Did not connect the crank breather back to the spark arrester as at this point I figured the coolant I saw behind the valves was as result of sucking in the steamy blow by not an actual intake coolant leak. At 3000 rpm steam is pumping out of the crankcase breather and dipstick tube. Shut it down and pulled off carb to swab the intake looking for coolant, nope dry. Enough is enough, pulled engine out of boat, put it on a stand and took it apart. Aha. I carefully inspected cyl #1 and finally found a tiny fissure about 3" down the cylinder wall. Into the truck (with a spare block I found locally just in case) and back to the machine shop. He verified with some sort of yellow magic powder and what looks like an electromagnet that there was a crack. He says it should be no problem to sleeve it and re bore the cylinder. Supposed to be ready for pick up by the weekend. Still going to cost be labour to do the sleeve and bore/assemble. Hope this time I can re install, bolt on intake, coolant, re install the drive and actually go boating. Not a great experience for me sending it out for rebuild! Crossing my fingers.
Alan

 

[Sangster21]

I got a call from the machine shop the day after I dropped off the block to be sleeved, (and I tried quite vigorously to leave the donor block there just in case) and was told the block couldn't be sleeved! Something described as a "core shift" in the casting process. Anyway another 220km round trip to drop off the donor block. They did do a quick turn around on the machine and assembly. Ready to go again. Installed engine, hooked up electrical and plumbing, turn ignition key and .... nothing. What the heck, I know I wired it up correctly. Maybe neutral interrupt, wiggle, wiggle, try again and not even click. OK lets look for voltage for start circuit at solenoid, rats battery dead in VOM. No problem I have another one, except that bat is dead too. Run off and get batteries. Check voltage, I have volts. Must be bad solenoid. Remove, try and it is no good. Buy new one at Lordco, install and also no good. Replace with old solenoid from Dad's toolbox and she starts first crank. Yessss.
Funny noise, oh no. Harmonic balancer wobbly. Dammit I have to wear this one, I knew better and tried pulling balancer with 3 jaw, didn't try very hard before I ran out to get a plate style puller. Obviously enough to distort hub from sheave. Pull drive, lift engine enough to pull balancer and now waiting for a new one. I must have done some bad in a previous life.
Alan