1979 454 Steam out covers and oil out dipstick
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1979 454 Steam out covers and oil out dipstick

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    Default 1979 454 Steam out covers and oil out dipstick

    I recently purchased a 1979 jet boat with a 454 it starts up and runs well, It never seems to get hot but late in the afternoon it did get steam coming out of the valve cover vents and out the dipstick tube. Brought it home and check compression one side is 125 125 125 130
    the other side 130 110 120 125. Did a leak down on the 110 cylinder and after 20 min it lost maybe 1 pound. The next day we went back up to the lake and at 3600 rpm (which seems to be max for the setup) it thru some oil out the dipstick on a fairly fast turn. We got a little steam also but we took it easy on it and only ran it around at 2500-2800 at 3500 it started steaming again. The engine has no smoke blow by at all that I can see, at idle it has no pressure what so ever. Anythoughts I am thinking maybe the intake is leaking water into the engine and it is a very small amount and it is boiling off before it turns the engine oil milky. Engine oil is black but there is milk under the valve cover and in the vent cap. It is possible the jet is over powering the water system it is 12JG A.

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    Only turning an A impeller 3600 means something is really wrong. Should be able to spin it 45-4800. Does it have a breather? Oil overfilled? Sounds like its really overdue for an oil change, prob a good tune up too.
    Does it have a t-stat?
    Last edited by 86NovaII; 10-16-2012 at 06:38 AM.

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    I just got the boat did not change oil but it did not look horrible but I will change it 454 in a boat any different than a truck 10-30 or just straight 30w. New plugs and points were in before first trip. Big block will be ok to 4500 rpm with basically stock engine? What do you make of the steam coming out. Engine has no t-stat do you think it should have one?? breather is a fairly large marine arrestor breather that came stock on the boat.

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    Or Seth, either one Budweiser's Avatar
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    Any "steam" you see coming from the breathers is in fact blow by gasses. A little bit makes it's way past the rings. Occurs on all piston engines. Most stock marine engines have a tube/pipe/hose that directs these gasses to the air filter/flame arrester, which allows the engine to consume the gasses instead of venting them to open air. There is such a thing as too much, however your description sounds normal.

    Your rpm's are interesting though. Something"s not right about that. Tach issue? Engine issue? Really an "AA" impeller? Who knows?

    My stock 350 pulls 4500.

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    When the engine is at idle or running low rpm's there is no gas venting period, it only starts after engine has been running awhile at high rpms the engine heats up and the steam issue starts up. It is for sure a A impeller unless it has been changed out internally. I am going to recheck the timing on it, and try to figure if the linkage is not getting full travel. Should this engine be running a T-stat, my temp gauge will not move off cold no matter how long I have been out( I am on third sending unit and second gauge). I dont understand how you get steam from a cold engine. Remember the valve cover and vent cap show milky oil but oil in the pan is black. The steam coming out has no smell it is not unburned fuel or smoke is disapates quickly.

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    Or Seth, either one Budweiser's Avatar
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    Quote Originally Posted by mdloper View Post
    When the engine is at idle or running low rpm's there is no gas venting period, it only starts after engine has been running awhile at high rpms the engine heats up and the steam issue starts up. It is for sure a A impeller unless it has been changed out internally. I am going to recheck the timing on it, and try to figure if the linkage is not getting full travel. Should this engine be running a T-stat, my temp gauge will not move off cold no matter how long I have been out( I am on third sending unit and second gauge). I dont understand how you get steam from a cold engine. Remember the valve cover and vent cap show milky oil but oil in the pan is black. The steam coming out has no smell it is not unburned fuel or smoke is disapates quickly.
    Blow-by gasses are not unburnt fuel, they are burned fuel... exhaust, so-to-speak. Piston rings do not contain 100% of the cylinder pressure, a wee little bit will seep past even the best of 'em. A wee little bit, a couple thousand times per minute, will look like steam out of the breathers. Blow by gasses (aka:burnt fuel, aka:exhaust) is very humid, per-se. Water is created in the process of combustion. Ever see water drizzle out of the tail pipe on your car/truck? That's where it comes from. The catalytic converter creates some too, but even a car w/o a catalytic converter will create water vapor in it's exhaust. When the exhaust system is cool (in the morning) the water vapor condenses into water and drizzles from the tail pipe. The valve covers get milky from oil mixing with condensation that collects in them when they are cool... Condensation from the water vapor created by combustion... The "steam" you see coming out of your breathers.

    The thermostat issue... Like skinning a cat.

    -Some use a thermostat in a bypass thermostat housing like this one from Rex Marine, which will cycle engine temperature between 160° and 190°.
    Rex Thermostat Housing


    -Some adjust the amount of water that is able to circulate through the engine by using a valve (ball valve, gate valve, etc.) until the engine reaches an acceptable temperature while at wide open throttle.

    -And... Some just run cold.

    Good thinking on checking throttle travel. It always seems the simplest things that are overlooked, cause the biggest headaches.
    Last edited by Budweiser; 10-16-2012 at 01:06 PM.

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    Quote Originally Posted by mdloper View Post
    When the engine is at idle or running low rpm's there is no gas venting period, it only starts after engine has been running awhile at high rpms the engine heats up and the steam issue starts up. It is for sure a A impeller unless it has been changed out internally. I am going to recheck the timing on it, and try to figure if the linkage is not getting full travel. Should this engine be running a T-stat, my temp gauge will not move off cold no matter how long I have been out( I am on third sending unit and second gauge). I dont understand how you get steam from a cold engine. Remember the valve cover and vent cap show milky oil but oil in the pan is black. The steam coming out has no smell it is not unburned fuel or smoke is disapates quickly.
    If you have milky oil on the valve covers, clearly you are seeing steam out of the breather once the engine oil get's to 212 degrees and is able to vaporize the water. That's why you don't see it at idle, you aren't heating the oil until you put a load on it.

    I would check water pressure in the block if you don't have it regulated from the jet pump in any way. Lots of guys run gate valves,, perhaps a better way is a pressure bypass that bleeds off excess water and pressure if you exceed the set amount.

    If the intake gasket is already compromised, you will almost certainly need to pull the intake to fix it. I would be concerned with pressure before you give any consideration to a thermostat.

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    Quote Originally Posted by obnoxious001 View Post
    If you have milky oil on the valve covers, clearly you are seeing steam out of the breather once the engine oil get's to 212 degrees and is able to vaporize the water. That's why you don't see it at idle, you aren't heating the oil until you put a load on it.

    I would check water pressure in the block if you don't have it regulated from the jet pump in any way. Lots of guys run gate valves,, perhaps a better way is a pressure bypass that bleeds off excess water and pressure if you exceed the set amount.

    If the intake gasket is already compromised, you will almost certainly need to pull the intake to fix it. I would be concerned with pressure before you give any consideration to a thermostat.
    Are you saying that the pressure from the 12jg A could be to much pressure for the engine, I was thinking that too but this seems to be the way it came from the factory, this boat is a really low hour original boat that does not look to have been done anything more than just driven. Is there a way to check the pressure or figure if there is excessive pressure there(engine) I was thinking that water was minor leaking from the intake and boiling off on the hot oil at high speed when the pump is at high pressure, but the engine oil shows no sign of milk at all.

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    Quote Originally Posted by mdloper View Post
    Are you saying that the pressure from the 12jg A could be to much pressure for the engine, I was thinking that too but this seems to be the way it came from the factory, this boat is a really low hour original boat that does not look to have been done anything more than just driven. Is there a way to check the pressure or figure if there is excessive pressure there(engine) I was thinking that water was minor leaking from the intake and boiling off on the hot oil at high speed when the pump is at high pressure, but the engine oil shows no sign of milk at all.
    Right, I would test it with a water pressure gauge while running the boat. Does the pump have a valve before the water gets to the block?

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