Oil Sample Analysis

PlaneGuy

Active Member
SILVER Sponsor
Jun 21, 2022
115
Huron Ohio
Boat Info
2000 340 Sundancer
Engines
Mercruiser 7.4L
When I changed the oil in my engines, 2000 7.4L Mercruisers with closed cooling, I took samples of the oil to have analyzed. I have done this on every boat I have owned. This was the first time I have sent them in since I just bought the boat in August. When the reports came back the lab noted that there was a trace of coolant in both engines. I have not had a chance to talk with my marine technician about this but has anyone else had this before? Just curious what I may be looking at. Thanks.
 
There's not too many places that can cause this. You can be looking at an early failure of a gasket from the intake manifold or a head gasket. Outside chance of the water pump gaskets leaking into the timing chain cover depending on which cover you have.
 
When I changed the oil in my engines, 2000 7.4L Mercruisers with closed cooling, I took samples of the oil to have analyzed. I have done this on every boat I have owned. This was the first time I have sent them in since I just bought the boat in August. When the reports came back the lab noted that there was a trace of coolant in both engines. I have not had a chance to talk with my marine technician about this but has anyone else had this before? Just curious what I may be looking at. Thanks.
How many hours on them? Good service records? Sure hope the head gaskets are OK, PITA repair!
 
How many hours on them? Good service records? Sure hope the head gaskets are OK, PITA repair!
Just under 900 hours. The boat appears to have been well maintained by the previous owner.
 
With just a trace, since you changed oil, I would run 15 hrs and re-sample. If its still there, further investigation - compression test, manifold gaskets.

Who did your samples? Maybe try another vendor - i.e. if you used Blackstone, use CAT SOS.
 
With just a trace, since you changed oil, I would run 15 hrs and re-sample. If its still there, further investigation - compression test, manifold gaskets.

Who did your samples? Maybe try another vendor - i.e. if you used Blackstone, use CAT SOS.
I did use Blackstone Labs which I have used them in the past. The oil had about 62 hours on it when I changed it in the fall. Blackstone did also mention to try a resample after putting some time on the engines next season. I think that is what I will do. Thanks.
 
For clarity, you took the samples in August and you mailed them to Blackstone recently? I like Blackstone, it's who I use. I do question the validity of your sample if it sat for 2+ months.

@SKybolt is right, you are looking at a head and/or manifold gasket issue. I chased this down on my previous 330DA after a sample showed antifreeze. Turned out to be a head gasket that got fixed under warranty.
 
For clarity, you took the samples in August and you mailed them to Blackstone recently? I like Blackstone, it's who I use. I do question the validity of your sample if it sat for 2+ months.

@SKybolt is right, you are looking at a head and/or manifold gasket issue. I chased this down on my previous 330DA after a sample showed antifreeze. Turned out to be a head gasket that got fixed under warranty.
No, I changed the oil in early October and sent in the samples at that time.
 
Is there an oil cooler in the closed loop cooling system on that engine?
A head gasket issue would typically blow the coolant out of the engine and/or show high CO2 in the coolant. That is, unless it was only leaking into the oil return holes.
Intake manifold leak into the valley is also a possibly.
 
Thanks for all the information. I will discuss this with my marine technician as soon as I can get up to Lake Erie. This darn thing called working for a living is getting in my way. Luckily I only have one more full year to do it.
 
I think Blackstone is $25. CAT SOS is $13...
You have to buy 10 kits, I think, for SOS. It's not a value for me since I may not own the boat for 10 oil changes.

I have used Blackstone for years and have a history with them, can look back to any sample. Nice thing to have.
This, plus I like the way they write their reports, like they are at the dock talking to me.
 

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