Mercruiser 165 - cylinder head?

[Sangster21]

I have posted bits of this previously, so here goes. Had my 250cu in I6 rebuilt in Nov by a reputable engine rebuilder. New pistons (.030 +) new cam, head redone (magnaflux, guides, valve grind, seals etc), full meal deal, didn't cheap out on anything. Fired up nicely, tuning on the muffs in the driveway, runs fine. Now comes an oops, rev the engine by hand and I had the idle cam in wrong and had throttle stuck open (engine racing) as long as it took me to run up and shut off ignition. Probably 5 seconds. A week later boat goes into the salt chuck for a sea trial, we run for a short time, discover we are starting to overheat (got up to 250 on gauge) and shut down. Turns out the throttle blip on the muffs totally toasted the leg water pump. Replaced pump. Finally got time last week to get the boat in the water again and run it. Runs fine happy happy, but I notice a whole lot of fluid that is condensing and dripping off the spark arrestor. Pull crankcase breather and it is puffing steam out a whole bunch.
I think this is not good so call it quits for the day and do some investigating. I pressure test the coolant system ( I have a San Juan cooling system) cold and it holds pressure. I run the engine on muffs again until it comes to temp and let it get hot. Again I note what I think is a lot of vapor coming from both dip stick and crank breather, again enough that it starts to drip out of the spark arrestor. I collect it in a can and I think it appears like coolant. I let the engine cool down enough to remove the rad cap and re pressure test the coolant system, we have a leak. In a few minutes it drops from 15psi down to 12 psi. I do not see any external signs of leak. I assume I have a head gasket issue.
I just pulled the head and don't see any obvious signs of a leak. I have done a quick check with precision straightedge and feeler guages and I find a max of about .002" out of flat on the cylinder head. Haven't had time to check the block yet. Also, the coolant which is essentially brand new looks pretty crappy, kinda cloudy and green/brownish... as if it was long overdue for a change.
Advice requested please.
I am going to give the head a really good cleaning and wire wheel the combustion chambers looking for cracks etc. Should I get it magnafluxed again? Should I pull the valves and inspect seats etc?
Do I need a marine specific head gasket for an engine that only sees antifreeze?
What else should I be doing before I put it all back together?
The engine rebuilder did have to do a thread repair due to crack in block on one of the front cylinder head bolt holes, he suggested this was not an uncommon issue with these engines, and it should be just fine.
Any words of wisdom from those that know would be much appreciated.
Regards,
Alan

 

[Bt Doctur]

Re: Mercruiser 165 - cylinder head?

did you use sealant on the head bolts?

 

[Sangster21]

Re: Mercruiser 165 - cylinder head?

It appeared there was sealant on the head bolt threads when I took the head off. I certainly will use sealant when I put it back together again. My manual calls for something called Perfect Seal for the threads, is there an automotive store version of this that is acceptable?

 

[alldodge]

Re: Mercruiser 165 - cylinder head?

It appeared there was sealant on the head bolt threads when I took the head off. I certainly will use sealant when I put it back together again. My manual calls for something called Perfect Seal for the threads, is there an automotive store version of this that is acceptable?

There are many manufactures for thread sealants. Below is one from Permatex which has been used by others on this forum in place of Perfect seal

Gasket Sealants : Permatex? Aviation Form-A-Gasket? No. 3 Sealant Liquid

You can find similar stuff from ARP, Loctite and a few others. The sealants are mostly in areas where a water jacket is present (IMO). I use torque lube and that last time it was ARP brand. Torque lube is basically antisieze and so long as your bolts are threads are ****=n=span clean, you will get a good torque.

 

[Sangster21]

The saga continues. Before I re installed the new head gasket, I checked the head and block for flat,all good. Head was only .0025" out of flat. I did not see anything when I took it apart that looked like a head gasket leak. I put it back together, adjusted the valves and started it up. Runs fine. I do still note some water/steam coming from the valve cover breather and oil fill tube. I drained the oil and replaced filter and new oil. Took it for a couple hours of running and still there is steam puffing from the valve cover breather, enough to result in a milky looking mess below the spark arrestor. I checked coolant level and I am down on coolant. There is creamy oil emulsion on the dipstick, but to be honest the oil is not all milky and emulsified. Signs of water in oil but I appear not to be making oil. I pulled spark plugs and 1-5 look pretty good, spark plug from #6 is quite wet. What the heck is going on? The intake manifold is very new and is on a closed system, only antifreeze circulates in it.
Help please with the trouble shooting process. I think right off I will do a compression test , and probably re do the coolant pressure test. I think I will have to remove the manifold and pressure test it, maybe there is a flaw or crack and I am sucking coolant into the intake? But wait a minute are they not twinned ports, wouldn't I get water in two adjacent cylinders?
Any suggestion for trouble shooting tests before I pull the head off again? I think I am going to call the engine builder on Monday and ask for his thoughts.
Alan

 

[TheShadow619]

Did you have the head re-magnifluxed? It really sounds like you cracked the head. Most likely in between the water jacket and the intake valve. Or the crack could be in the cylinder wall, but that's highly unlikely.

 

[Sangster21]

I did not have the head magnafluxed, I looked very carefully, but I did not have it magnafluxed. If there was coolant getting into #6 combustion chamber, how do I end up with the moisture that presents itself in the crank case? If there is significant coolant intrusion into the combustion chamber is it then just a small amount that leaks past the rings that ends up contaminating the crank? I haven't topped up on coolant, but my overflow tank has emptied itself on the last run, and I haven't "made" oil in the crankcase. As I said, it showed signs of water contamination, but not the milkshake effect. I don't have access to a compression gauge today or I would rush off and do a compression test.
Any further thoughts on my situation are welcome!
Alan

 

[TheShadow619]

Yes. The moisture signs in the oil can come from coolant leaking past the rings. Remember when you shut off the engine there is pressure still in the coolant system that will push it into the cylinder. Or it could be cracked in 2 places. Into cylinder 6 and to the oil galley through the head. A good sign of water in the oil, with no rise in oil level, is cream under the oil fill cap. I'm 95% sure you have a cracked head.

 

[Sangster21]

I did a compression test tonight, and found all cylinders between 120 and 130psi. Seems somewhat low for a freshly rebuilt engine, but perhaps the rings are still sealing or the guage is reading low. There was definitely what The Shadow noted as cream under the valve cover. The combustion chamber sure do not show signs of cracking, I wonder if there is a crack in the intake runner that extends into the water jacket that ends up with coolant into the combustion chamber when the valve opens on intake stroke. I inspected #6 cylinder at bdc, but did not see anything that looked like a crack in the cylinder wall.The intake manifold (essentially brand new) does not show any signs of coolant leaking into the intake passages.
How will the machine shop check the head for leaks ? Do they have some means of pressure testing or will just magnaflux to check for cracks?
I am also wondering if I have an issue with the manifold, when I pulled of the exhaust elbow and looked into the exhaust manifold it had some
raw water and rust signs inside.Shouldn't the water discharge that cools the elbow just cool the down side of the elbow and go straight down the exhaust? Anyway I guess my first step is to take my cylinder head in for inspection and go from there. If my head checks out I guess I will pressure test the manifold.

 

[TheShadow619]

From what I found, factory spec is about 130, so I think you're fine on compression. I have a 1969 Mercruiser 165 and there is a PCV line that runs from the top of the valve cover to the carb. Do you have that? If so, I bet that's where the steam out of the spark arrester is coming from. So...you are getting coolant into the crankcase, but not thru a cylinder. It is either a cracked head between the coolant passage and an oil return passage or a bad spot in the head gasket where the water transfers from the block to the head to an oil return passage. The reason it has to be going to an oil return passage is that you do not have water in a cylinder when you pressure the cooling system, and you are not getting oil in the water, which would happen if it was cracked to a pressured oil galley (engine running=oil pressure higher than water pressure=oil in water). It is not a cylinder problem. Therefore I think your manifold is fine also.
Pull the head and carefully inspect the head gasket for a sign of water passing from a water passage to an oil return passage. If nothing found, have head checked. And yes, they can pressure test the head or magniflux it, or both.

 

[Sangster21]

I had the head inspected at the machine shop, it was magnafluxed and pressure tested, the shop claims the head is sound. I think I may be chasing around several issues. I did find some signs of water (salt) getting to cylinder #6. I checked and found a somewhat suspect block off plate between manifold and riser, made a new one and installed fresh gaskets after checking the riser with solvent for leaking. I changed engine oil again and sea tested.
I am still losing coolant and seeing signs of vapor from crankcase vent and at spark arrester. After a good 40 minutes of running hard I had to shut down due to the amount of steam barfing from the crankcase vent again. I am having a hell of a time trying to troubleshoot this issue!
Checked engine oil and shows clear, a small bit of emulsion up on dip stick but not in body of oil. No emulsion is present on the rad cap. As a previous poster had noted, oil is at higher pressure than coolant, so if there was an in block rupture between oil gallery and coolant passage, you would think I would find oil in the coolant. There is no sign of oil in the coolant.
If my cyl head is good, then I suspect my 1 year old manifold may have a slight leak allowing coolant into the common intake runners allowing coolant to be ingested into the combustion chambers. My next step is to pressurize my manifold and check for leaks there. This is really wearing me out! Engine runs like a top except for the steam!
Again, if anyone has some words of wisdom for me with regards to trouble shooting... would be much appreciated.
Thanks.