Coolant overflow

[Mr O]

Seemed like a simple problem to fix when a small amount of coolant came out of the overflow tube into the bilge. The engine is a Volvo Penta md22 pb which has a pressure cap and no overflow tank. The original cap has some hairline cracks in the brass plate that contacts the flange, so I bought a new cap. Still pukes coolant when motor has been running at normal operating temp.

Manual says coolant must be above fins inside header tank. I've been filling to just below filler opening. Am I simply overfilling or is there some other cause?

Engine temps are normal, coolant never dumps more than about 6-8 oz. strainer is clean and lots of water coming out exhaust. Circulation pump issue?

Thanks in advance for any suggestions.

Mr O
2001 HR39 cutter

[nigel1]

My guess is the coolant is overfilled. With the expansion from heating and heel of the boat, it's likely to overflow.
Next time, don't refill, but keep a check on the coolant level. If it continues to overflow, it's a bigger problem.

[Kenomac]

I had a similar issue last season which resulted in a very surprising conclusion. Our hot water heater tank coil had sprung a pinhole leak due to corrosion, which then resulted in pressurized freshwater overfilling the engine coolant. When we ran the engine, antifreeze coolant would leak out and overflow into the overflow chamber and cap.

It was quite the mistery until someone on the forum solved the puzzel.

https://m.youtube.com/watch?v=SWBgkKh66sc

[Stu Jackson]

Get a small Rubbermaid bottle and put the overflow line into it.

[delmarrey]

I went to a wrecking yard and pulled a overflow tank from a car and installed it on the boat. Now the coolant flows both ways just like on a car. No waste, or loss!
(Down under the motor on the right)


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[Mr O]

My hot water tank has been drained for the winter, so freshwater is not getting into the coolant. However, the heat from engine causes pressure in the tank which has forced water left in the lines to shoot out of the sink tap! Maybe I should close the valve from engine to hot water heater?

Regarding the adding of a overflow tank, I would think that the standard cap would not allow flow of coolant back to heat exchanger tank. Special cap needed?

Thanks, all!

[delmarrey]

Originally Posted by Mr O

My hot water tank has been drained for the winter, so freshwater is not getting into the coolant. However, the heat from engine causes pressure in the tank which has forced water left in the lines to shoot out of the sink tap! Maybe I should close the valve from engine to hot water heater?

Regarding the adding of a overflow tank, I would think that the standard cap would not allow flow of coolant back to heat exchanger tank. Special cap needed?

Thanks, all!

Heat exchangers are just like radiators. When they cool down they create a vacuum sucking the coolant back into the system. If you inspect the caps you will see they are spring loaded to create 10-15 # of pressure. Also they might have a secondary valve/seal that allows the coolant to come back in. See picture.
If not, you can purchase a new automotive cap that does have the secondary valve.


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[Mr O]

Nigel, I think you are correct. The coolant that gets dumped out the overflow tube is always about the same volume and never more than 6-8 oz. After the engine cools, that coolant gets sucked back into the filler from the container I connected to the overflow hose. What's confusing to me is that the manual says to fill coolant to the filler neck, which I did several times and each time it's up to temp the coolant dumps into the bilge. Since the level is always slightly above the minimum, it's probably ok to leave it at that.

[delmarrey]

Originally Posted by Mr O

Nigel, I think you are correct. The coolant that gets dumped out the overflow tube is always about the same volume and never more than 6-8 oz. After the engine cools, that coolant gets sucked back into the filler from the container I connected to the overflow hose. What's confusing to me is that the manual says to fill coolant to the filler neck, which I did several times and each time it's up to temp the coolant dumps into the bilge. Since the level is always slightly above the minimum, it's probably ok to leave it at that.

If you fill it to the neck when cold, it will expand with heat, and dump out the tube when hot. When it cools it will shrink and leave a void at the top, UNLESS there is coolant in the tube to bring back in. If too low the engine water pump will start to cavitate and will not circulate properly.
The problem with not having an overflow thank, is over time you'll lose some of the coolant thru evaporation with no way to replenish it with out constantly pulling the cap.
And what happens to the waste stuff? You pump it overboard or have the special absorbent pads to collect it?

[Mr O]

Originally Posted by delmarrey

If you fill it to the neck when cold, it will expand with heat, and dump out the tube when hot. When it cools it will shrink and leave a void at the top, UNLESS there is coolant in the tube to bring back in. If too low the engine water pump will start to cavitate and will not circulate properly.
The problem with not having an overflow thank, is over time you'll lose some of the coolant thru evaporation with no way to replenish it with out constantly pulling the cap.
And what happens to the waste stuff? You pump it overboard or have the special absorbent pads to collect it?

Yup, I agree. The stuff that spills into my bilge was shop vacced up and taken to the local hazardous waste facility along with old oil and filters, etc.