Did I only change half my coolant?

jameswilson29 · #1 (**permalink**) 12-05-2011

I removed the drain plug at the bottom of the engine block of my Vetus M3.10 diesel inboard and drained almost a gallon of antifreeze out of the engine. It flowed out much faster after I removed the coolant filter cap, but I was not able to find a second drain plug to unscrew on the heat exchanger, as instructed by the manual. It appeared all the coolant drained out of the heat exchanger.

The technical data in the manual indicate the capacity in litres of the cooling system is 7 litres. I re-filled new coolant in a 50/50 mixture with water in the same amount I removed - about 3.5 litres.

Did I leave 3.5 litres unchanged in the engine block (which will mix with the new coolant) or does the stated capacity for the cooling system include the raw water portion?

(The manual appears to be written by a native German speaker who learned English.)

JimsCAL · #2 (**permalink**) 12-05-2011

Could be you still have large pockets of air in the system. You may find you need to add more after you first run the engine.

LakeSuperiorGeezer · #3 (**permalink**) 12-05-2011

Air in the engine from closed thermostat. You can severely overheat the engine if you run it with only half the coolant, especially the head where all the heat is. Sometimes there is a small vent hole in the thermostat. If you wait an hour, you can add more if lucky; otherwise, you have to find a way to bleed the air out. Maybe you can loosen the temperature sensor to bleed the air if it is located on top of the head. Maybe there is some other way as I am not familiar with the engine.

jameswilson29 · #4 (**permalink**) 12-05-2011

Thanks for your responses.

I replaced as much as I drained out, so there should not be any net loss. The engine has been running fine since I bought the boat a month ago. I just thought perhaps the capacity discrepancy could be explained by coolant in the block that did not flow out for a change because I did not loosen a drain on the top of the other side of the block and that all I changed was the coolant in the heat exchanger.

Maybe the capacity figure in the manual is incorrect?

tdw · #5 (**permalink**) 12-05-2011

Remember that I don't live in a cold climate so while our engines might use coolant, anti freeze as such is not necessary.

So , why do you need to change the coolant/anti freeze. Sure I keep it topped up but I've never changed the coolant in any vehicle nor boat I've ever owned. (Current boat is first fresh water cooled boat I've owned so not real experiecne with this.)

(That could be misunderstood ... I'm meaning to ask why is it necessary to change the coolant/anti freeze ? Does it loose it anti freeze ability after a year or so ?)

MarkSF · #6 (**permalink**) 12-05-2011

Quote:

Originally Posted by tdw

Remember that I don't live in a cold climate so while our engines might use coolant, anti freeze as susch is not necessary.

So , why do you need to change the coolant/anti freeze. Sure I keep it topped up but I;ve never changed the coolant in any vehicle nor boat I've ever owned. (Current boat is first fresh water cooled boat I've owned so not real experiecne with this.)

Because the coolant contains anti-corrosion additives, which eventually become exhausted. When that happens, the cooling system components begin to corrode. A normal coolant is depleted in 2-3 years, while a coolant with organic-acid corrosion inhibitors should last 5.

tdw · #7 (**permalink**) 12-06-2011

Quote:

Originally Posted by MarkSF

Because the coolant contains anti-corrosion additives, which eventually become exhausted. When that happens, the cooling system components begin to corrode. A normal coolant is depleted in 2-3 years, while a coolant with organic-acid corrosion inhibitors should last 5.

Well there you go, I didn't know that, now I do. Thank you.

MarkSF · #8 (**permalink**) 12-06-2011

Quote:

Originally Posted by tdw

Well there you go, I didn't know that, now I do. Thank you.

You are most welcome! But your post got me wondering, why don't boat and car manufacturers just put a zinc electrode in the fresh water system? One protects the sea water circuit from corrosion OK.

jameswilson29 · #9 (**permalink**) 12-07-2011

Update: The mechanic in the yard who hauled my boat out said the gallon I removed was likely the entire amount.

It appears that the POs had not changed the coolant since the engine was last painted - probably 15 years ago - because the drain plug was sealed to the engine block with paint. The old coolant was a noticeably darker color than the new coolant, but had no solids in it.

I will try to find the other drain plug next year, but even if I am only changing half the fluid annually, at least a much higher percentage of the coolant will be relatively fresher over time as I replace half each year.