Mercruiser 470 Coolant Loss and Milkshake Oil

[emmurphy50]

Hello all... I have an odd situation.
After a great two weeks in the Adirondacks, I came home and after not getting my boat to start at the ramp on a night I was short on time with my kid, I brought it home. I found my coolant was gone out of the reservoir (and also the reserve tank) and found my oil to be milkshake brown. I drained the oil and found the first 1/3 of the oil drain to be pure coolant.

I pressure tested the cooling system at the reservoir, and it kept 20 psi for much of a day. I am sure that the bladder was not sealed against the reservoir bottom (i.e., I tested the system not sealed the tester). I had this happen before and it was intermittent. I drained the oil and flushed with fresh cheap SAE30 and changed the filter and filled with diesel SAE30 which has the ZDDP I like.

I filled the coolant, took almost two gallons, and turned the engine over a bit to get the fresh oil moving. Would not fire. Pulled the plugs, look decent. Did a compression test, got 90/75/85/90 on the cylinders 1-4 (front to back). I came back a few days later after the coolant level being stable, and it was all gone again, and in the bottom of my oil pan (drains Mt. Dew for 5-8 seconds before milkshake oil).

Where is it going? Good place to start tearing down? No coolant I can see out the water pump weephole, and it's clear.

Thanks,

 

[Eric 3.7LX Alpha 1]

Did you get it running after you changed the oil and topped off the coolant the first time, you mentioned you turned it over but not if it started?

Did the motor run hot/overheat at all before this happened?
Here is the possible causes for water in the oil from service manual 8

 

[texans543]

Hello all... I have an odd situation.
After a great two weeks in the Adirondacks, I came home and after not getting my boat to start at the ramp on a night I was short on time with my kid, I brought it home. I found my coolant was gone out of the reservoir (and also the reserve tank) and found my oil to be milkshake brown. I drained the oil and found the first 1/3 of the oil drain to be pure coolant.

I pressure tested the cooling system at the reservoir, and it kept 20 psi for much of a day. I am sure that the bladder was not sealed against the reservoir bottom (i.e., I tested the system not sealed the tester). I had this happen before and it was intermittent. I drained the oil and flushed with fresh cheap SAE30 and changed the filter and filled with diesel SAE30 which has the ZDDP I like.

I filled the coolant, took almost two gallons, and turned the engine over a bit to get the fresh oil moving. Would not fire. Pulled the plugs, look decent. Did a compression test, got 90/75/85/90 on the cylinders 1-4 (front to back). I came back a few days later after the coolant level being stable, and it was all gone again, and in the bottom of my oil pan (drains Mt. Dew for 5-8 seconds before milkshake oil).

Where is it going? Good place to start tearing down? No coolant I can see out the water pump weephole, and it's clear.

Thanks,

Ouch! Sounds like you have a head gasket leak to me. Also, looking at your compression each should be with in 10% of each other. You might have a cracked block, Start from the top of the motor work your way down.

 

[Eric 3.7LX Alpha 1]

Ouch! Sounds like you have a head gasket leak to me. Also, looking at your compression each should be with in 10% of each other. You might have a cracked block, Start from the top of the motor work your way down.

These blocks don't usually suffer from being cracked, they're aluminum not cast iron and all have closed cooling with antifreeze, not sea water. Not to say it couldn't happen....

They do blow head gaskets pretty easily if the overheat though.

 

[Scott Danforth]

two sources of coolant to crank case leaks

source 1 - water pump / cam snout seal
source 2 - head gasket

 

[achris]

two sources of coolant to crank case leaks

source 1 - water pump / cam snout seal
source 2 - head gasket

My bet's on option #1.

Chris..

 

[nola mike]

Did you check to make sure that the weep hole is clear?

 

[emmurphy50]

Did you check to make sure that the weep hole is clear?

Yes. I don't see leaks out the weep hole...

 

[emmurphy50]

Did you get it running after you changed the oil and topped off the coolant the first time, you mentioned you turned it over but not if it started?

Did the motor run hot/overheat at all before this happened?
Here is the possible causes for water in the oil from service manual 8
View attachment 348666

It's not water it is coolant...

 

[emmurphy50]

Did you get it running after you changed the oil and topped off the coolant the first time, you mentioned you turned it over but not if it started?

Did the motor run hot/overheat at all before this happened?
Here is the possible causes for water in the oil from service manual 8

Did you check to make sure that the weep hole is clear?

Yes

 

[Eric 3.7LX Alpha 1]

.

 

[Rick Stephens]

The inner seal goes on the water pump - where does the coolant go?

 

[achris]

Did you check to make sure that the weep hole is clear?

Yes

How did you check it?

 

[emmurphy50]

My bet's on option #1.

Chris..

I would agree but I can literally almost say water go from The Fill into the oil pan. I just did what my mechanic said and pull the elbow off first to see if the seals went bad cause and coolant to go into the exhaust and back into the engine they look pretty good

How did you check it?

I took a toothpick and make sure the weep is clear

 

[Scott Danforth]

time to drain the coolant and pressure test.

should hold 15psi forever.

however since we know its not, pressureize it and listen for where its leaking.

 

[achris]

I took a toothpick and make sure the weep is clear

You are going to need something a bit longer than a toothpick. That hole is about 15cm long.

 

[emmurphy50]

time to drain the coolant and pressure test.

should hold 15psi forever.

however since we know its not, pressureize it and listen for where its leaking.

I pressure tested it with most of the coolant in the oil pan it appears to 20 psi and it stayed for hours.

 

[emmurphy50]

You are going to need something a bit longer than a toothpick. That hole is about 15cm long.

You think that inner seal being bad would have the coolant just straight drain into the oil pan from the coolant side as it's being filled? Thanks for the tip - any ideas on how to clean it?

 

[Scott Danforth]

Something not adding up

If its the cam snout seal or the head gasket, it wont hold 20 psi

If the water jacket is empty and you tested pressure to 20 psi and it held, you dont have a leak

 

[emmurphy50]

Something not adding up

If its the cam snout seal or the head gasket, it wont hold 20 psi

If the water jacket is empty and you tested pressure to 20 psi and it held, you dont have a leak

I agree. I don't know if it was totally empty, but the coolant drained signficantly, and when I pulled the drain plug into the bilge, the first 4-6 seconds was Mountain Dew, followed by chocolate milk shake.