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oil samples with positive for glycol

infinityron

Contributing Member
This will probably be viewed as dumb question because I am experienced boater (50 years) and diy engine mechanic but.......I'm considering the purchase of an older Tiara with twin 7.4 fwc engines. Coolant looks clean and full in the heat exchangers, oil is not milky and looks ok visually. I pulled samples for testing at SOS and starboard came back positive for glycol. My experience tells me theres only one way for glycol to get into oil on a fwc engine, and that is through head gasket (or a cracked block). Sea trialed this boat and it performed well. No smoke or steam to speak of. Cruised at 3000 rpms and achieved a little over 4000 when opened up. Temps stayed under 160 and verified with ir.

I called a trusted mechanic and asked his advice. I want the boat but that glycol result is causing me concern. His feedback was that in his experience, that glycol could have been introduced by some previous event and no amount of oil changes gets rid of every trace. He advised proceeding if I love the boat and good deal.

But I value opinions here.
 
What previous event would introduce glycol get into oil system? No normal events come to mind with me. Has a static coolant system pressure test been performed? How does it hold pressure? What about compression test and a good inspection/comparison of spark plugs? Also, shouldn't those engines see 4800 to 5200 on a wide-open run?

For your sea trial, I'd think that you would want to see the engines cut out by rev-limiter at high rpm. This will demonstrate full engine capability and show that the props are correct. Look for steam after a minute or so of a hard run.

Good luck, Noel.
 
How were the wear metals on the engine that was + for glycol? If higher than the other engine, for sure there is wear taking place due to the glycol in the motor oil. Any "event" that allows glycol into motor oil is not a good thing. I did a few oil analyses on my old 1988 4.3 Chevrolet in our boat and the season before the head gaskets blew (probably previous overheat damage) sodium (from salt water cooling) showed up in the oil sample. So that's a warning that you may at the least have to do head gaskets on that engine, you can also get AF in the oil if the intake gaskets leak, it will put coolant right into the cam valley & motor oil. R+R the manifold and replacing gaskets is not a big deal on GM marine engines. However, if there is any sign of glycol in the cylinders, that's gotta be a head gasket, cracked head or block.
 
Thanks to you guys for responding. What I meant by previous event was that if that engine head a head gasket go a few years ago, and even if it was replaced and put back together, it seems possible to me and to my mechanic that barring a somehow miraculous flushing of the block and complete sanitation of the pan etc, that residue glycol might still show up on an oil sample...... at any rate, it is true that other than the labor of tearing it apart, the task of ding the head gaskets on these engines can be done by a good diy guy with tools. I have torn down boat engines before a few times and lifted them out with a tractor or forklift to take to shop for rebuild and put them back in. I love this particular boat and within budget. I looked at long blocks from Rapido Marine, and it looks like a reman long block is about $3800. I think I will buy this boat and take my chances. Change the oil a few times and retest. On sea trial the temp did not get above 160 and no steam. If I need to replace that engine, I can strip it down to ready to hoist, have a long block ready at the yard and pay for the crane service to lift out the old and drop in the new. Then put the rest of it back together. I'd rather not but.....maybe I'll get lucky.
 
Go back & compare the wear metals, if they are about the same then the mechanic who advised you might be right. If they are much higher then just factor that into the overall boat budget.
 
Go back & compare the wear metals, if they are about the same then the mechanic who advised you might be right. If they are much higher then just factor that into the overall boat budget.

looking at the wear metals and an oil lab document on normal ranges....aluminum is within range both engines, chromium is with in range both engines, copper is elevated both engines (reference paper says that is usually oil cooler), iron is elevated but almost equal both engines (range is below 100ppm....results are 168 and 179), lead is within range both engines, but higher on the one positive glycol, tin is within range both engines. Sodium in both engines, but higher on the glycol one.
 
looking at the wear metals and an oil lab document on normal ranges....aluminum is within range both engines, chromium is with in range both engines, copper is elevated both engines (reference paper says that is usually oil cooler), iron is elevated but almost equal both engines (range is below 100ppm....results are 168 and 179), lead is within range both engines, but higher on the one positive glycol, tin is within range both engines. Sodium in both engines, but higher on the glycol one.

I forgot 0 soot either engine, which implies 100% combustion?
 
it just means zero soot measured in the oil...I'd seriously doubt you'd see 100% combustion...


I'd be a bit leery but not knowing the details of the engine (hours, time since last change,etc) or the test (minimums of each element it reliably detects) its hard to say definitely. I looked up the details of gylcol and believe it would be possible to have a 'trace' if the intake was removed and some residual coolant made it back into the crankcase...but can't tell you how long it could or would remain.


I'd also be inclined to get a full leakdown test run, just to get an idea of the mechanical condition...the sea test results (based on your discussion) sounds ok.


If you can do the work then you can save a bunch of the labor expense if something goes unplanned...good luck...
 
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