Rear Cylinders moisture

[drem312]

Recent rebuild 1989 omc 5.7 bored over .30 Block is a 95-2000 according to the die cast numbers.Did a break in period . The motor was running perfect for about ten hours total time over the course of 2 weeks . I did an oil change at about two hours in then put in 5w-30 it was recommended because Im runniing a cooler engine with 143 thermostat. Fished offshore all day ,stopped at one spot idle and drifted for about 45 minutes when I went to head home,the oil pressure read 20psi,usually stayed 40-60. I stopped the boat checked the oil it was full and I didnt hear any engine noise.Figuring it might be a bad gauge I started back in. About 15 minutes later slight ticking noise in the valve train. Put boat on trailer headed home. Had mechanic checked the guage it was fine did a pressure test at the back of the intake, oil pressure 20 psi at idle then would drop to 15psi when given the gas. I yanked the motor out of the boat yesterday the mechanic broke it all down and the two rear cylinders have rust and some moisture. The plugs do not look porcelian white from steam. The manifiolds did run in salt water before I bought the boat but did not replace them,I was told they were new.I did tear them apart before the engine rebuild and bought new risers gaskets and cleaned alot of scale out of them but they did appear to be solid with thick metal in between.Question is, The motor was built tight very tight in fact even with it all broken down the crank(still connected to the pistons) seems hard to turn no heads on no plugs in. All bearings seem ok also. If my manifolds are good ,can a motor pull water, with back pressure, back into the rear cylinders? I have Omc Log manifolds. What else would cause the two cylinders to have rust in them ,would a crack head or intake? The oil was dirty muddy grayish color but not milky or coffee creamy color. Reference the oil pressure the pump is good, there werent any spun bearings,the cam spun ok. Any ideas on rust and pressure prioblems the motor was ran the day before the mechanic took it apart and 4 days from the ocean trip

 

[Lou C]

Re: Rear Cylinders moisture

Well for one thing, even with a 143 thermostat, I would not run a 5w-30 in a marine engine, in fact Merc recommended either straight 30 at temps up to 50* and straight 40 at temps over 50, before they came out with their 25-40 oil. Volvo recommended 20w-50, or straight 30 depending on the years, and OMC recommended straight 30. Multi vis oils, especially one with a 5w rating are going to shear down under sustained high rpm use of a marine engine. So I think you have two problems going on, one that oil is not the right one and probably got sheared down under normal marine use, I'd have changed the oil after verifying that you only had 15 psi. The other problem is the water intrusion, it could be the manifolds, it could be the gasket sealing surface between the riser and manifold. How low does the boat sit in the water? On this site, there is a sticky that tells you how to check manifolds for leaks using acetone. Did you see rust stains in the exhaust gas portion of the exhaust manifolds? I just changed my one piece units on my 88 OMC, they were starting to clog, but I never had any water intrusion. Here is what they looked like after 5 1/2 seasons in salt water, as you can see the exhaust ports in the engine (original '88 engine) show no sign of water/rust.
Back to the oil issue, I have used straight 30 and 40, I switched to straight 40 because of the age of the engine, and it had been starting to use a bit more oil. I have good compression, and there was no smoke either on the water hose or in the water. No oil in the exhaust water on the hose either. When I pulled the manifolds, I did see a bit of oil around the intake valve on the rear most cylinder on the starboard side, so its either the valve seal or guide. Not worth a rebuild, salt water motor, so I just keep it topped up with Chevron Delo 400 straight 40.

I'd carefully check those manifolds again, are your flappers in the Y pipe in place? Any doubt about the manifolds replace em. I have heard that running cool, can on some set-ups cause condensation in the exhaust, which if you idle a lot, can cause a problem. Maybe that's why, all OMCs, most Volvos, had 160 stats even before the move to EFI. Late model Mercs all seem to have 160 stats too. At cruise 3500 rpm my new manifolds top out at about 135* with the IR heat gun, at idle they are about 100-115....

 

[drem312]

Re: Rear Cylinders moisture

Thank you for you reply and info.I put a 143 in there becuase I did get some info that the cooler water helps the salt no build up in the engine and manifolds.I did install new flappers in the y pipe they were not there when I removed the old engine.The boat does not sit in water I trailer it but this boat has only been on the ocean water twice and the lake three times before that.The 5w I put in I should of known. I figured since I was thhinking out of the box using a 143 I would be better off going with the 5w and not the SAE 30 as recommend by the manual.Well it has to be rebuilt now anyway since the mechanic tore it all apart . I think I will add the 160 thermo and then SAE30.I know all inside is good I shut things down pretty quick and the rod bearings and cam look like they never got hot at all.Do you think the theory of a tight engine sucking some water back in thru or near the engine is possible causing some moisture to settle in the two rear cylinders ?

 

[Lou C]

Re: Rear Cylinders moisture

I don't think the engine being built on the tight end of the tolerances would make a difference per se, but it is possible for any marine inboard to suck water up the exhaust under the right (or wrong depending on how you look at it) circumstances. If the stern of the boat sits low in the water (static water level, ie the level that the water rises up to in the Y pipe) is a factor on some boats, I recall reading you have to have at least 13" from the water line to the top of the risers or else you can suck in water. This can happen if you make a sudden stop, or back up too fast, or idle for a long period of time and the exhaust cools off and then you can get some condensation, which can be sucked in. Certain camshaft grinds (esp high performance auto cams) can make sucking in water worse. But in your case, make sure your manifolds are good, make sure the risers are good as well as the gaskets. That's the most common way water gets in.
good reading....



http://www.michel-christen.com/ExhaustElbows.pdf

 

[drem312]

Re: Rear Cylinders moisture

Thanks again I did tear apart and clean them and put new gasket in between but I will acetone them now they are off again to see what I can find

 

[HT32BSX115]

Re: Rear Cylinders moisture

Thanks again I did tear apart and clean them and put new gasket in between but I will acetone them now they are off again to see what I can find

Howdy,


Um, how old are your manifolds and risers?

 

[drem312]

Re: Rear Cylinders moisture

I was told they were new and had little use. The outside looked great the inside had alot of scale from sitting. I cleaned put new gaskets and ran some hot water thru them and couldnt see any obvious leaks. I thought more than one cylinder would be affected if they were bad. It seems a small amount of water like condensation is the culprit. The original engine builder is coming up Sunday to check the rest of the main bearings.

 

[HT32BSX115]

Re: Rear Cylinders moisture

I was told they were new and had little use. The outside looked great the inside had alot of scale from sitting. I cleaned put new gaskets and ran some hot water thru them and couldnt see any obvious leaks. I thought more than one cylinder would be affected if they were bad. It seems a small amount of water like condensation is the culprit. The original engine builder is coming up Sunday to check the rest of the main bearings.

You really do not get condensation in manifolds.

If they leak, the water doesn't get into the engine until you shut down (it's blown out with the exhaust). If it's a riser leak, water above the riser gasket can run back into an open exhaust valve........

BUT, it would be a different one each time the engine stopped unless the engine stopped at exactly the same place (same stroke) each time. If water is in the same cyl each time you may have a head gasket leak or cracked head etc.

.I did tear them apart before the engine rebuild and bought new risers gaskets and cleaned alot of scale out of them but they did appear to be solid with thick metal in between.

New manifolds are not "plugged" with rust but in salt it doesn't take long.


I would have pressure checked the cooling system before pulling the heads off. you might also want to check out the intake manifold. They sometimes are pretty rusty in the water t-stat area and can also leak....

 

[drem312]

Re: Rear Cylinders moisture

Thanks. I will let you know what the engine builder says this Sunday

 

[Lou C]

Re: Rear Cylinders moisture

read this article, note that it says that below 110 degrees, you CAN get condensation in the exhaust manifolds, now with a 160 stat, my engine idles at about 165 on the gauge, the intake manifold below the thermo housing is at about 155 degrees, the manifolds are around 115 degrees...that's why I stuck with a 160 stat, even though people talk about salt coming out of the water at higher temps, I have not seen this to be an issue as of yet....now in the article they talk about warm manifolds and cold manifolds (plumbed differently), OMC's design is more like a warm manifold system, but still mine are just above the threshold of condensation.....this is esp true if you do a lot of low speed trolling when fishing...or have to idle through many no wake zones...I'd put the 160 stat back in, test it first to make sure it opens and closes right and replace the manifolds and risers if there is any doubt to their condition....
The fact that OMC and Volvo both used only a 160 stat on these systems, and never offered a 143 stat as an option, tells you something.....

the way the OMC water flow works, when you start a cold engine all the cold cooling water goes out the manifolds through the bypass in the housing while the thermostat is closed and the water in the block re-circulates. When the thermo opens, it allows the hot water in the engine to pass out the housing and exit by the manifolds, and the cold water entering the thermo housing is pumped into the engine by the circ pump and then cools the engine, then exits the engine via the manifolds. So if the engine is running too cool (143 thermo) it is possible to have a cooler than optimal temp in the exhaust manifolds....


http://www.perfprotech.com/store/articles/warm-manifold-cooling-tips.aspx

 

[drem312]

Re: Rear Cylinders moisture

Excellent info thank you

 

[HT32BSX115]

Re: Rear Cylinders moisture

Lou,

I kinda think the amount of water that would condense in a manifold might be enough to cause rust in the manifold, but do you think the article is implying it would be enough to produce liquid in the same 2 cyls on every shutdown?

If water was indeed condensing in the exhaust system (in the above case) the engine would have to stop at the same position every time too, or there would be water in other cyls since the same exhaust valves wouldn't be open.....


Same with a riser leak I suppose.....

 

[Lou C]

Re: Rear Cylinders moisture

You know it's hard to say, some other articles I read on this subject did not specify the amount of water you might see or which cylinders would be more so affected...but they did say, that some risers were designed with a hook in the bend, to keep the vacuum that can exist in the exhaust pulses from pulling the condensed moisture up over the hump in the riser and down into the manifold, but some do not. Merc used something called a turbulator ring on their dry joint exhaust to prevent this problem, so maybe its for real on some engines, operated in certain conditions.....

http://www.ebasicpower.com/faq/dryjointexhaust.htm