Strange Theory about Engine Overheating

[Auspicious]

Originally Posted by Moody46CC

I'm all ears to your experiment with barnacle buster, first as to how you will do it, and second, if it works.

I'll let you know. When Mastervolt sold off their generator business I kept track of the guy that was their lead customer service mechanic. I've been following his guidance.

Originally Posted by Moody46CC

Cheechako: planning on replacing the sensors, but I can try to by-pass them. I suppose the way to do it is to remove their leads.

Check the sensors. If I recall one was NO and one was NC.

Originally Posted by Moody46CC

Gilow: have not noticed any oil in water. Oil looks normal. I am going to have an oil analysis done in fall for both the genset engine and the main engine. Was going to do it last fall and just forgot. The water temp in Va is fine for diving under the boat and trying to insert a length of hose in one of the seacocks. But the jellyfish are not fine. Got to play that one by ear this coming weekend.

A five gallon bucket full of water makes a good place to put the intake hose and allow you to rule out interaction between the inlet and outlet. Keep a hose handy in case you need to refill the bucket for an extended run.

Originally Posted by Moody46CC

Socaldmax: my mechanic mentioned your theory about the thermostat, but it has overheated with it in and with it out. I am going to replace it. I can take the temperature at the inlet side (thermostat housing or just before it) and at the exhaust elbow just below the valve where the water is injected into the gases.

You can test the existing thermostat in a saucepan of water with a thermometer. Whether you test the existing 'stat or a new one (or both) it's nice to know you have a good one before you put it in.

[Ex-Calif]

Originally Posted by Moody46CC

I did put a new radiator cap on the coolant tank--not the expansion tank, but the coolant tank on the top of the engine block.

When it overheats, one can hear the boiling and see bubbles of air going from the coolant tank to the expansion tank. The latter is connected with clear tubing. And no, the actual coolant amount has not dropped. I put a tick mark on the plastic expansion tank, and when things settle down after overheating the coolant fluid level returns to the tick mark.

Ouch...

My dollar is with the head gasket crowd.

Bubbles and overheating are not a good combination.

OTOH - It is not the worlds most difficult fix. Just don't run it hot anymore as cracking the head is a distinct possibility.

[DeepFrz]

Just on the off chance that the thermostat was replaced, does it have a small 1/16" hole in it just where the two pieces are bonded together? If not drill one and see if that makes any difference. It would also be good to make sure the heat exchanger is clean and clear of debris even is that job is a PITA.

Good luck.

[socaldmax]

Before sailorchic came up with the head gasket theory, I was starting to lean toward a heat exchanger problem. If there is corrosion or barnacles on one side of the heat exchanger, or impeller bits, blocked passages, etc. it might cause the engine to overheat, especially if one replaced the coolant cap with a weak/defective or poorly sealing one.

The question is, which comes first, the bubbles, or the over heating? If you see bubbles when the engine is cold or at normal temps., then the head gasket theory is the best. If it gets really hot, then the cap opens up at too low of a pressure, you might just be seeing boiling coolant, possibly caused by poor heat exchange. This is where it's helpful to check temps all over the place, inlet and outlet of seawater, inlet and outlet of coolant, even each exhaust port just to make sure equal fuel is burning in each cylinder.

Diesel engines are very simple, there is no magic to them, especially mechanically injected, non turbo ones. When you do find the problem, it always makes perfect sense when you look at the symptoms you had.

Good luck!

[sailorchic34]

The overheating can be intermittent as the cooling system is still rejecting heat, but under load the hot combustion gases can overheat the coolant faster then it can be cooled.

It's not too big a pain to change a head gasket. Continued running with a blown head gasket can cause head warping, cracked head/block and all sorts of fun. Best to have it changed sooner rather than later.

Odds are you may need the manifold gasket too as you may need to remove the coolant tank to get the head off, depending on how your engine bay is arranged. Best to have the head/block checked for flatness too. Probably OK. Not a bad time to put new hoses on too.

With continuous bubbling there are only two things it can be. The blown head gasket is the better of the two and low cost compared to a cracked block/head

[a64pilot]

Combustion gases in coolant is a real easy thing to check for,

this is a ink to one available tester, you may even find one locally, or maybe a local mechanic would have one.
http://www.amazon.com/UVIEW-560000-C.../dp/B000NPDL76

[a64pilot]

Originally Posted by DeepFrz

Just on the off chance that the thermostat was replaced, does it have a small 1/16" hole in it just where the two pieces are bonded together? If not drill one and see if that makes any difference. It would also be good to make sure the heat exchanger is clean and clear of debris even is that job is a PITA.

Good luck.

A small hole in the thermostat also makes life a lot simpler when trying to purge all of the air out of a cooling system, the hole will slowly let the air out, no hole and it's trapped

[Moody46CC]

If this helps, I only get the bubbles in the coolant after the engine has overheated and shut down or I shut it down. I've put a heat gun on the thermostat, and when it rises to 220, I know it's going higher and will shut down at 230F, so I have shut it down. I can hear the air discharging and see the air bubbles in the tubing running from the outlet at the radiator cap on the engine coolant tank to the expansion tank, located on a bulkhead 2' away.

[sailorchic34]

Originally Posted by Moody46CC

If this helps, I only get the bubbles in the coolant after the engine has overheated and shut down or I shut it down. I've put a heat gun on the thermostat, and when it rises to 220, I know it's going higher and will shut down at 230F, so I have shut it down. I can hear the air discharging and see the air bubbles in the tubing running from the outlet at the radiator cap on the engine coolant tank to the expansion tank, located on a bulkhead 2' away.

As Emily Latilla would say, that's different. That is the coolant boiling, well the air in the water, venting caused by coolant boiling, from the heat of the engine

Have you checked that the coolant passage in the discharge elbow is clear. You can check by blowing into the hose that connects to the discharge elbow. They can get clogged rather easily.

You can also check the flow from the hose to the discharge elbow via bucket. Only need to run it for a few seconds to verify flow. Not enough to damage the exhaust hose.