Engine Coolant Loss

[Chief Engineer]

The overflow tank only works when the water in the engine expands with heat.

When the engine cools water is drawn back.

I would suspect a bad cap or fitting for cap on heat exchanger.

You should keep the coolant level in the overflow tank at the proper mark to allow for expansion.

What did he pressure test to.....Did he pressure test the cap?

[JiffyLube]

Maybe the coolant is escaping into the raw water side of the heat exchanger through a leak, then being exhausted out with the raw water.

[GordMay]

There should be NO pressure drop over 2 hours, excepting as might be caused a LARGE & rapid temperature change.

[doug86]

It could certainly be as simple as a radiator cap, but then I would expect OP to see evidence of leaking or weeping around the cap neck; he reported that he hasn't seen any leaking anywhere.

Could also be a very small leak in fresh water circulating pump and the evidence of that has eluded detection. Is the V belt clean? A tiny water pump seal drip can end up being flung to far away places in the engine room and not leave any real drip on the engine surface. Use an inspection mirror to look at the inside surface of the pump pulley; it should look dry and clean on a one year old motor.

A thorough inspection of every possible leak source might turn something up. With a new installation, the most likely answer is a tiny drip from a hose clamp or slightly loose gasket seal someplace.

And, finally: check the coolant recovery system itself for leaks. The hose to the recovery bottle could have a small leak, or the bottle itself could have a small crack? Put some clean sorb rags underneath and see if you have a drip there.

[rabend]

He tested to approximately 15 PSI and the system operates at 7 PSI. There is no leak whatsoever at the fresh water pump or the heat exchanger cap. I have ordered a "block tester" to check for exhaust gases in the heat exchanger area. I am also going to block the water heater hoses to eliminate any issues there. My "engine room" is really small, and I carefully cleaned the tan fiberglass pan under the engine some time ago so that I would see any coolant that might be leaking out. Thanks for all your suggestions and comments. This discussion has really helped me think through the problem.

Regards,

Bob

[doug86]

Originally Posted by rabend

Just an added note: The engine technician told me that a heat exchanger leak would cause salt water in the coolant since the pressure on the salt water side is higher than the fresh water side.

He is wrong.

Originally Posted by DeepFrz

And as far as pressure difference goes, The coolant side of the system would be at a higher pressure than the sea water side. Otherwise, why would you have a pressure cap on the coolant side of the engine cooling system with a warning about releasing the cap when the engine is hot? Sea water flows through the system in a very low pressure circuit.

DeepFrz is correct on this. There is almost no pressure in the salt water circuit because it is open at one end. An impeller pump can pressurize a system, but only if you restrict or stop the output flow at some point. A small hole in the heat exchanger usually pumps coolant into the raw water circuit.

So, your mechanic now has 2 strikes against him: he tested you system with admittedly faulty test equipment, and he doesn't really understand the plumbing dynamics of the engine.

If this is still under warranty, I would be on the phone to the regional Yanmar Distributor and demand some satisfaction.

[rabend]

I am working with the local Yanmar Distributor. That is where the technician came from.

Bob

[Chief Engineer]

With a proper radiator Tester, you should be able to start the engine.....bring it up to operating temperature and observe the pressure in the fresh water side of the cooling system.

This guy doesn't seem to be a Technician......You need a mechanic.

Where are you located?

Light a fire under Yanmar

[JiffyLube]

Originally Posted by doug86

He is wrong.

"Just an added note: The engine technician told me that a heat exchanger leak would cause salt water in the coolant since the pressure on the salt water side is higher than the fresh water side."

I know from personal experience that raw water can enter the heat exchanger system through a leak, but if it did it would over flow the expansion tank...not the problem this owner has experienced.

On our Pathfinder engine there is one special hard rubber boot caps on each end of the heat exchanger (each boot cap takes two hose clamps), designed to separate the raw water side from the engine coolant side. Once my engine over flowed at the expansion tank, and it wasn't from over heating. I flushed the coolant, installed another refurbished tube stack in the heat exchanger (a back up), installed new boot caps and hose clamps, and refilled with new coolant mixture...I had no more over filling of the expansion tank. I took the replaced tube stack along with an extra head exchanger I have to a radiator shop I use for testing, and the replaced tube stack checked out good with no leaks. The problem was with the hose clamps not clamping around the boot caps good enough, letting raw water enter into the coolant side of the system. So it is possible for raw water to enter the coolant side, and I check the hose clamps periodically for tightness.

[rabend]

I just wanted to comment that this distributor and mechanic have done work for me before. While I am by no means an engine mechanic, I am an engineer and can usually tell whether people know what they are doing by asking the right questions. These guys have always done stellar work for me in the past, and they are performing this current work at no charge. They are also well trained. My main reason for this post was to gain a better understanding of the problem and to get other opinions. Thank you all for your contribution to this topic. The discussion has been really informative for me and I learned a lot. Thanks again!!

Regards,

Bob

[rabend]

Just an update: Since the mechanic visit and his "milking" the fresh water line and adding coolant. The level in the overflow tank has remained constant over 20 engine hours. I am now sure he was right about the bubble in the hot water heater system.

Regards,

Bob