Can you test for a bad head gasket?

[FreddyTT]

1988 5.7 merc with Apla 1. I changed my engine oil yesterday. The oil on the dipstick looked clear and decent but what I pulled out looked light brown. I bought the boat from my friend a couple years ago who had the top end of the motor rebuilt two years before I bought it and the head gasket was replaced then. This year will be three to four years past that repair. Is there a test I can do to see if the head gaskets are bad?

Otherwise all I know how to do is check the oil on the dipstick after each lake day. Since the dipstick came out clear the first time I am not 100% confident I am seeing a problem by using the dipstick method.

 

[alldodge]

I could use some clarification for clear and brown colors. Most oil is a light brown color when new. Over time it gets a little darker, but when checking on the dipstick, it looks clear because the film is thin. It only starts looking darker the more the oil is used, so it takes some time to get the dip stick to show.

Your not seeing a milk color are you?

 

[Rick Stephens]

When you changed your oil did you inspect the oil at all afterwards? If there is water in it, that water will sink to the bottom. If in doubt, pour off the top 3/4 or so and dump the rest in a clear jar and set it aside. It will separate some of the water if it has water in it.

 

[DeepBlue2010]

If water leaked to the oil pan, you would have found white streaks in the oil. You can use the crackle test

http://www.machinerylubrication.com/Read/301/visual-crackle-oil-test [h=1][/h] or send a sample for analysis if you have strong doubts.

 

[FreddyTT]

No white streaks. I removed about 4 quarts as far as I could tell. I had to add 4.5 quarts total after replacing the filter and starting the engine. The dip stick looked clear, light. The stuff I took out was golden brown colored. Uniform color. Not dark, not clear, looked golden brown and thin I assumed because it was warm. What has changed since last oil change was the pump I used. My engine is old and the threads are bugard up on my engine that the Mercury pump threads on to. I think the last time I only got about 3-3.5 quarts out using that pump because I didn't get a good seal. This time I used a pump that goes down the dipstick hole and got out a more this time.

I have been doing a ton of work on my boat the last couple of years and did not do an oil change last year because I only took it out 4 or 6 times total. I had fuel problems last year (carb and fuel pump...exhaust leak) that cost me most of the summer sitting out paying for repairs. I didn't see any water separation or streaks.

 

[alldodge]

had fuel problems last year (carb and fuel pump...exhaust leak

Ya know, if your fuel pump was leaking it would put gas in the pan

 

[GA_Boater]

Ya know, if your fuel pump was leaking it would put gas in the pan

And depending much gas is in the oil, there may a gasoline smell.

Has your oil level gone up between changes?

 

[FreddyTT]

Oil level up...no. It was full on the dip stick before I pulled it out. I had a lot of gas smell in the boat last fall right after they did the work. My Rochester carb had a bad accelerator pump, the fuel pump was bad because there was no gas getting to the carb and the fuel separator was half full when we pulled it off. I sprung an exhaust manifold leak that same day. The boat was hard starting cold, and toward the end, I couldnt get over 1000RPM or it would choke out and stall. It died that day, had to get towed back to the dock. (I do have a mechanical fuel pump in that boat). Maybe that would explain it. Maybe there was some fuel in the oil from all that nonsense late last year that thinned it out a little bit and discolored it rather than water. It wasn't horrid. Just caught my attention when I poured it out of the pump into the oil pan I have. Im going to take it back to the mechanic to replace the top housing seal kit since I found the lower seal all mangled when I pulled the lower drive off to replace the water pump kit. I was thinking about having them run a test on the head gasket. They said there was a way to check that. I know you can on a car, not sure about boats though.

 

[GA_Boater]

Probably a compression and leak down test.

 

[wrench 3]

On an inboard boat engine I put clear hose in the cooling system between the thermostat housing and the manifolds and check for gas bubbles with it running.

 

[Rick Stephens]

What lower seal was damaged and do you know why? A bunged up seal in the lower gear case would have no bearing on the seals in the upper case. Typical price I have seen for resealing an upper is $300-$400. Pricey. If you are talking about the lower seal on the upper case, then what tears those up is twofold - running with the o-ring on the shaft that comes out of the lower and sticks into the upper case. That o-ring should be left out when you install the lower. The second reason that the upper seal gets torn up is installing the lower while the upper is on the boat. It is really easy to do damage trying to lift the lower up and not hit the seals. FAR better to pull the whole outdrive and disassemble-assemble them off the boat - lower the upper down onto the lower case maintaining careful alignment.

If in doubt as to the seals on your outdrive, pressure test your complete drive (see the stickies for a build it yourself pressure tester). I would not just go to a dealer and start replacing seals until a pressure test or a leak told me I had a problem.

Unless you had overheating issues I wouldn't bother with the head gasket testing. Not a likely source of problems unless the motor got really hot at one time. If the water pump in the outdrive was always kept in good condition, the motor will usually run very cool, which makes head gasket problems unlikely. testing a head gasket lean into the cooling system is MUCH harder on an open cooling system. It is possible to rust out a head gasket, takes quite a while on a freshwater boat with marine head gaskets.

Rick

 

[stonyloam]

Test for bad head gasket, do a compression check. All cylinders should be within about 10% of each other. If you have a significant amount of oil in the oil it will turn milkey and opaque as the water is emulsified and mixes with the oil.

 

[bruceb58]

Test for bad head gasket, do a compression check. All cylinders should be within about 10% of each other.

Need to do a cylinder leak down test in addition. Compression test alone doesn't tell the whole story.