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1975 GL1000, I havent had it out of storage in maybe 10 years. I was going through refreshing everything and the oil drained out milky which is indicitive of coolant. I had done the core plug replacement per the service bulletin when i first got it. So my question is this.
If i do a compression test will that show if a head gaskets blown and on which cylinder??

it could, very good chance. Leak down will give you what your looking for.

A cylinder leakdown test may be best practice to locate a possible leak.
Apply the pressure and listening into the oil fill hole. Pull the rocker arm covers off too.

My though was if a cylinder shows a way less compression that the others would be the indicator. that make sense??

Won't hurt to compression test for sure

CHUCK HAHN wrote: ↑Wed Oct 01, 2025 3:53 pm My though was if a cylinder shows a way less compression that the others would be the indicator. that make sense??

I had one that compression tested good, but water poured out of one of the cylinders when I put water in. Sometimes a leaky head gasket can act like a check valve. Lucky for me, it was leaking only into the cylinder. Laid up for 10 years in a humid environment, mild contamination could be condensation, too.

Also, I’ll add that once you pull all the plugs out to do the compression test there’s a very good chance that the spark plug in the offending hole will look “steam cleaned” or rusted from the water in the cylinder… Onceyou pull the plugs line them up and post a picture here.

In my experience a compression test may show you the leaking cylinder but it may not as well,, a leak down test has a better chance of telling you but as Cliff said above pull the oil fill cap and the valve covers and listen for an air leak coming through the crankcase,, you can also do this by just putting air pressure in the spark plug hole and listening if you don’t have a leak down tester. I’ve experienced a lot of blown head gaskets over the years in various motors and can tell you that some times it’s just a matter of compiling the results.. Let us know !

So as i understand it, if the head gaskets blown there will be a whitish exhaust plume. Not a blue smoke like oil but a whitish steam kinda exhaust. Is that also a good indicator? Basically im looking for what to do first.. Start it and see how the exhaust looks? Start it then look for water wet plugs?? Do compression check before even starting it?
I will add that it had nice green antifreeze in the block when i drained the water pump so i think i can eliminate a cracked water jacket from freezing. AND i took the engine out to replace clutch plates and fix the starter clutch and upon draining oil for these repairs is when the milkshake oil was found. Looked like a peanut butter colored shake. Engine been put back in the frame already.

Just had a maybe crazy idea to check for a cracked water jacket. Since i havent mounted the radiator yet what if i fashioned a set up to the thermostat housing to connect the airhose to and blow air into the water jacket and listen to the oil fill hole for air passing into the crankcase??
Theoretically the water jacket and crankcase should be totally separated unless theres a crack. Make sense?? Air sounds in crankcase from the thermostat housing taking in the air could only mean cracked water jacket is my idea.

Was it low on coolant?

Yes. only about a pint came out of the water pump drain bolt. Its been so long since i had it out last i cant honestly remember any water related issues. I got it sold but i gotta make it right first. I have ordered head gaskets and if ot needed i can return them.
I should add the bike has a tad over 89,000 on the clock

Got to thinking about how much came into the pan when i drained the oil. It wasnt more than you'd expect when doing an oil change. Im thinking if it had 4 quarts of oil and the 3 quarts of antifreeze as the manual calls for dtain pan would have been close to overflowing however it wasnt close to overflowing.

Tests sound like a good idea.

You didn't have a crankcase of oil plus most of a radiator/motor full of coolant.

If there's no clear indication in easy tests, before digging deeper I'd likely fill with 10-40 motor oil and distilled water, run the bike like you would to get it going after long dormancy, and pay attention to coolant levels, steam out the exhaust, and, of course, water in the oil (or the reverse). But maybe I'm less cautious than others.

it doesn't take much water to make oil milky. And depending on the temp. changes during storage for that length of time, it could be condensation. Getting it running is a good idea before you tear into it. But start it and keep a close eye on it as it runs thru a couple of het cycles

I also have been looking at parts fiches and it looks like the water pump has an internal oring that, to me, looks like it seals the impeller shaft. And i think if thats shrunk up and brittle water can bypass into the crankcase. Im no genius but i understand basic engineering as far as how i see it in the fiches.
I ordered both orings shown and theyll be replaced. Im not sure how to link pictures but you can view the water pump fiche to see how they configured it.
Im gonna replace both pump orings. Cant hurt anything knowing they're good