Coolant Disappearing, need help

[Dinows]

Mercruiser 8.2, engine runs great but when I check the following morning coolant jug almost empty, refill and same thing happens after running and sitting overnight. no leakes I can find anyplace. The coolant is going someplace ?? Any ideas ?

 

[alldodge]

Serial number?
What does the oil look like?

 

[Scott Danforth]

either you have a leak into the raw water side or the oil/combustion side.

drain the coolant, do a pressure test. fix the issue.

 

[cyclops222]

Weird head & intake gasket leaks will suck out out and put it into cylinders.
Check how each spark plug looks. 1 or more may show the oil burning problem locations.

 

[04fxdwgi25]

Sure sounds like a head gasket or leaking heat exchanger.

 

[Dinows]

Serial number?
What does the oil look like?

Oil is clear, no issues there, thanks

 

[Dinows]

Weird head & intake gasket leaks will suck out out and put it into cylinders.
Check how each spark plug looks. 1 or more may show the oil burning problem locations.

OK thanks, engine runs like a charm ??

 

[Dinows]

Sure sounds like a head gasket or leaking heat exchanger.

If it was a head gasket wouldnt it run a little rough ?

 

[Dinows]

either you have a leak into the raw water side or the oil/combustion side.

drain the coolant, do a pressure test. fix the issue.

The fumy part is I can run the thing for half an hour and do not loose any coolant, but when I come back the next day coolant jug is almost empty !!

 

[Scott Danforth]

Fluid expansion when heated. When you key off, heat soak will force the coolant out somewhere

Pressure test the cooling water system (after draining)

 

[Dinows]

Fluid expansion when heated. When you key off, heat soak will force the coolant out somewhere

Pressure test the cooling water system (after draining)

Ok I am loosing pressure, but how do I find out where it is going ? This is a low hour engine that has always run like a charm. Oil is perfectly clear, runs smooth as a baby's butt ?? What do you think ? Thanks

 

[Scott Danforth]

Low hours just means it sat. In a boat, 50-100 hours a year is normal usage

Now you start pressure testing components such as the heat exchanger, exhaust elbows, etc.

 

[alldodge]

Serial number?

number?

 

[cyclops222]

Wait 15 minutes after shut down. Check for oil around the boat. All your refills would have filled the bilge ?

 

[stresspoint]

If it was a head gasket wouldnt it run a little rough ?

maybe , maybe not ,that said ,
i have seen small blocks with rotted out exhaust ports do the same as your BB , non of them showed any sign of running bad , just coolant disappearing

 

[04fxdwgi25]

Until he does a pressure test and the stuff mentioned here, there is not a lot of use rehashing everything. Everything can't be okey dokey and coolant still vanishing unless it's something obvious like a bad radiator cap blowing off early / when pressure rises for a few minutes after shut off.

 

[tpenfield]

In order to find the leak, you can do another pressure test and listen for the air escaping. You may need a mechanics stethoscope in order to locate it.

 

[cyclops222]

Could a person be sucking the oil out with a little battery pump ? Just to cause you grief ? Bad joke ? We are getting close to that kind of crap.

 

[04fxdwgi25]

OIl??? His problem is engine coolant vanishing.

 

[Dinows]

Wait 15 minutes after shut down. Check for oil around the boat. All your refills would have filled the bilge ?

Not a bit of coolant in the bilge, dry as a bone