AQ 151 spitting oil out of the oil trap

A.Parks

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Jan 2, 2018
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I am thinking I have a bad head gasket but need help to diagnose. It seems that there is oil coming from the oil trap at RPMs over 1500 it starts spitting oil into the air cleaner. If the engine sits and idles it blows white smoke out which I assume is just blow by gasses from the bottom end but if you increase the rpm speed it starts to throw oil out like a fountain and the oil is milky in color like a blow head gasket. If you check the dipstick the oil is nice and clear in fact just changed it yesterday. The motor overheated about a month ago cause the belt on the water pump broke but it has run strong since then and doesn' overheat now either. I took to the spot we usually put in today and it started right up I let it sit and idle for at least 30 minutes and the temperature was around 180 degrees and the oil pressure was close to 60 psi. This is all coming from the hose that connects under the air cleaner to the oil trap.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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White smoke is usually water in the combustion chamber. When you overheated it, you most likely toasted your head gasket. Pull the plugs and look for signs of moisture. Do a compression test to check health of pistons
 

A.Parks

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I am going to do a compression test hopefully tonight. I do think it is the head gasket as well but what I don't get is the boat overheated months ago and has run strong ever since. So we went away for the New Years weekend for 3 days with the boat it ran great for the first 2 days the 3 day is when the issue started , mind you we ran about 8 hours each day. The overheating issue was at least a month prior to this.

Should I just assume it is the head gasket and just replace it? basically rebuild the whole top end?
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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NEVER ASS-U-ME anything. diagnose, diagnose, diagnose

there are no shortcuts
 

A.Parks

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Jan 2, 2018
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Finally got a chance to do a compression test. Cylinder 1 &4 where good and 2&3 where bad. I removed the head and noticed that the gasket between the combustion chamber and the cooling holes was blown out. If everything goes right I should be able to get it all back together this weekend. Thanks for the information Scott
 

Bondo

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If everything goes right I should be able to get it all back together this weekend.

Ayuh,...... Welcome Aboard,...... Have Ya cleaned, 'n checked both the head, 'n block for Flatness,....
 

A.Parks

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Thank You!! Yes, I put a straight edge across both the head and the block ( length and width ) and it all looks good to me. Should I do something else? are there issues with these units warping that I should know about?
 

Bondo

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Naw,.... Cleanin' the surfaces nice, 'n Clean is sorta skipped by many Diy'ers,....

Checkin' for flatness is often not even thought of,....

Many times there's erosion in the area of the head gasket failure,....
Depends on how long, 'n how hard run,....
 

Lou C

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Nov 10, 2002
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11,802
There are specs for flatness, that you measure by laying a straightedge lengthwise and width wise, and see if a .004" feeler blade fits under, it should not. The spec for small block Chevrolets is .003 so I am just using that as an example. You should check what Volvo's spec is to make sure. I would probably want to take the cyl head to an automotive machine shop and have it cleaned, and checked for cracks. Then take that time to do a valve job, check the valve guides and replace the valve seals. The hardest part of this job is the cleaning and getting the block deck totally clean as well as the cyl head bolt holes. They must be clean to get proper cyl head torque. On some engines you have to replace the head bolts when you remove them, because they stretch when tightened.

I had a bad overheat in 2013 and then the engine ran fine with normal compression for 2 more seasons. However, I did a Blackstone analysis on the engine oil and salt was beginning to show up in small amounts. This was the beginning of head gasket failure which manifested itself in August of 2016. I blew out all the water and fogged the heck out of it, drained the block and manifolds. Did some diagnostics and found that even though the comp. test results were still ok, exhaust gas was getting into the cooling water. And then the front 2 cyls would gradually get water in them again after a few days. So took it apart. Brought heads to machine shop. Found both had cracks in the center cyls exhaust valve seats. Also the cooling passages were getting eroded from salt water use and might not seal well. Cleaned it all up and installed a pair of re-man marine heads. Added a new Volvo style center riser exhaust system. Although truth be told, the OMC batwings never leaked on me, in 15 years of salt water use. Going to replace the old Q-Jet with a Holley 4160 set up for the V6 in the spring.
 

A.Parks

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Jan 2, 2018
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Thanks for all of the advice!! I put the engine back together on Saturday and it is running great!! it fired right up and idles smooth. I however didn't replace the sealing rings on the raw water pump so there is a leak coming from the 2 on the pump and the one on the exhaust manifold but not bad. I ordered new ones which should be here tomorrow and on the boat by Saturday morning.
 
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