Damage from Overheating?

[oldjags]

Our engine overheated today due to the hose clamp on the hose from the engine to the water heater coming loose, and all the coolant leaking out. The engine started slowing down and in about 4-5 seconds came to a complete stop - seized up.

We sailed for the next hour or so, repaired the hose, refilled the coolant, and then fired the engine back up. It seems to run fine and sounds normal. Any way to know if the engine has been damaged? It's a Yanmar.

[model 10]

First off I would remove the oil filter and cut it open and check for metal. You very well may have scored the cylinder wall and rings. It's easy to see what you have then . Any thing else is just a guess.

[roverhi]

Without taking the engine apart there is really no way to be absolutely sure. There may be indications that the engine needs a rebuild. Some of the those are hard starting when cold, oil in the water or vice versa, excessive smoking under normal loads, overheating, etc. The Yanmars are tough engines. Overheated mine when the seawater intake became plugged. Put 159 hours on it since with no issues. Cast iron heads make a big difference in tolerance to overheating. Do that with an aluminum head and the engine would be toast.

Discovered the overheating only when the boat filled with a fog of steam from the boiled away coolant. No coolant left in the engine and water sizzled on the head. Did not run it till it seized, however. Cleaned out the intake, refilled the coolant and it's run fine for 150 hours since. Not a good idea to run engine till it seizes but you may have dodged a bullet.

[WillJacocks]

If you added water while the engine was hot, you can crack something in the engine. Otherwise, you should be fine unless the overheating was a bit extreme.

[Ziggy]

I would guess that you probably reduced its remaining lifetime, but if it runs to your satisfaction I'd cross my fingers and continue to use it.

However, you should definitely change the oil and filter ASAP, and repeat this several times. I'm pretty sure that the oil you had in the engine has been destroyed by the high temperature. Also, it is likely that there is a lot of metal in the oil, so you want to flush it out.

[model 10]

Originally Posted by WillJacocks

If you added water while the engine was hot, you can crack something in the engine. Otherwise, you should be fine unless the overheating was a bit extreme.

Did you read his post? It siezed up.

[oldjags]

When I sensed that the engine was slowing down, I throttled down to idle, and that's when it stalled, so hopefully when it seized, it wasn't under much load. I waited for over an hour before adding more coolant and restarting.

Does the Yanmar not have a high-temperature alarm? I don't have my owner's manual with me. If it does, then mine is not working! If not, how hard is it to add one?

[John A]

Originally Posted by Guy

Did you read his post? It siezed up.

That would be my main concern. A piston expanded due to the high temperature and adhered to the cylinder wall. Once it cooled down the engine was able to be restarted. Damage has been done to the piston/cylinder wall the question is, how much? If the engine was operating at high rpm's there would have been damage to the connecting rod.
If you have further overheating issues you may have blown a head gasket.

IMO I like my engine to quit only when I want it to! I'd have someone pull the head and inspect for damage.

[Ziggy]

Originally Posted by oldjags

Does the Yanmar not have a high-temperature alarm? I don't have my owner's manual with me. If it does, then mine is not working! If not, how hard is it to add one?

I think all Yanmars have a high temp alarm, but yours may not be working properly. Also, I think it senses the coolant temperature. So if the coolant runs out it might not go off.

[jkangas]

Originally Posted by oldjags

Does the Yanmar not have a high-temperature alarm? I don't have my owner's manual with me. If it does, then mine is not working! If not, how hard is it to add one?

Mine has a temperature gage and a high temperature alarm...

[roverhi]

In my case, the PO had ditched the alarm for a gauge. Great idea but the gauge was buried by the wheel pedestal and took a yoga position to see it. Gauge is a bad idea if it's not easily observed. Had the problem with the temp gauge on an MG not sensing temperature because there was no water in the cooling system. Gauge read fine until I'd shut the engine down then slowly climbed into the red. Fortunately, just driven it around the block so it hadn't gotten very hot. That was a bulb type gauge, don't know how an electric senser would work.

Throttling back may have saved your bacon. When an engine seizes at working rpm, usually something big like a rod breaks. Continue to use the engine until you get some other indication that there is a problem. May get by just fine or have nocked a few hundred hours off of the end of life time. Spending money on it, other than changing fluids, without indications is probably a waste of money. If I was going on a cruise to the Antarctic it would be a different story. An oil analysis of the extant oil and one again about 20 hours after an oil change would give you an indication of where the engine is headed.

[sartorst]

You oil pressure and the temp alarm utilize the same piezoelectric buzzer and should sound every time you turn the key to the on position! as was mentioned before the temp sensor will not sense an overheat with no coolant on it! If it had truly seized it would not have restarted ! all the things mentioned above are GOOD ideas

[oldjags]

Originally Posted by Ziggy

I think all Yanmars have a high temp alarm, but yours may not be working properly. Also, I think it senses the coolant temperature. So if the coolant runs out it might not go off.

OK, I'll have to check that out, as that is definitely possible. All the coolant ran into the sump under the engine, so the sensor may have been dry when it overheated.

[Brogan007]

The design of many marine engine's protective alarm / shutdown, is a bloody disgrace.
Like a previous post mentioned...over heating alarm sensor is in the coolant...REALLY ? ( Yes ) So if you lose a hose, you're screwed!
I've lots of experience with Cat 3208TA engines frying exhaust manifolds due to this reason alone. Pathetic.
Had to install aftermarket fresh water level alarms ourselves.
Would it not seem sensible (?) to have a standard shutdown based on another technique.....

[model 10]

Originally Posted by Brogan007

The design of many marine engine's protective alarm / shutdown, is a bloody disgrace.
Like a previous post mentioned...over heating alarm sensor is in the coolant...REALLY ? ( Yes ) So if you lose a hose, you're screwed!
I've lots of experience with Cat 3208TA engines frying exhaust manifolds due to this reason alone. Pathetic.
Had to install aftermarket fresh water level alarms ourselves.
Would it not seem sensible (?) to have a standard shutdown based on another technique.....

Sure CHT for one but in the end it's up to the operator to pay attention.