Air Lock in Closed Cooling System

[sneuman]

I believe I have an airlock in the cooling system (heat exchanger/exhaust manifold, etc) that is preventing coolant from circulating. I can't find an obvious place to drain the system. Can I eliminate the problem by filling all the hoses in the chain or must I completely drain everything and start from scratch?

BTW, the engine is an Isuzu C240, if that helps.

[mesquaukee]

Never heard of an air lock in a cooling system. I'm assuming it is not the raw water side. Everything is so large and open. The water freely flows down to the pump.
It is more likely you have a stuck closed thermostat or the coolant pump for some reason is not pumping. Perhaps a loose impeller?

[sneuman]

Originally Posted by mesquaukee

Never heard of an air lock in a cooling system. I'm assuming it is not the raw water side. Everything is so large and open. The water freely flows down to the pump.
It is more likely you have a stuck closed thermostat or the coolant pump for some reason is not pumping. Perhaps a loose impeller?

It's not the raw water side and not the thermostat. It could be the pump, but the suggestion from the local "Table of Knowledge" has been that it's an airlock. I too had not heard of such a thing.

[Endojoe]

Is all I can personally speak from in this case. That said, I have seen it happen on a few different vehicles, often there is a plug of some sort in either the thermostat housing, or one of the housings that connect a hose to the engine block. Sometimes this may be a Allen (internal hex) type plug that is virtually flush with the housing. Another possibility to bleed out the air is to pull (or possibly just loosen) the coolant temperature sensor, if its accessible. Same goes for the plug, generally just loosening it enough to allow a steady dribble of water will also give the air an avenue of escape as well, and you should see some bubbling as the air escapes. Also, depending on the design of the system, just leaving the radiator cap off would be the simplest method of purging the system, just be careful with that for reasons which should be pretty self-evident. Below is a crude example of what I mean by a 'plug' in the housing, this is actually a plug taking the place of a temperature sensor, a typical plug would be much smaller, but you get the idea. Also worth noting, the thermostat housing may not be the only housing that serves as a hose-to-engine interface, often there is more than one housing that could easily be confused for a thermostat housing at a casual glance.

[sneuman]

Originally Posted by Endojoe

Is all I can personally speak from in this case. That said, I have seen it happen on a few different vehicles, often there is a plug of some sort in either the thermostat housing, or one of the housings that connect a hose to the engine block. Sometimes this may be a Allen (internal hex) type plug that is virtually flush with the housing. Another possibility to bleed out the air is to pull (or possibly just loosen) the coolant temperature sensor, if its accessible. Same goes for the plug, generally just loosening it enough to allow a steady dribble of water will also give the air an avenue of escape as well, and you should see some bubbling as the air escapes. Also, depending on the design of the system, just leaving the radiator cap off would be the simplest method of purging the system, just be careful with that for reasons which should be pretty self-evident. Below is a crude example of what I mean by a 'plug' in the housing, this is actually a plug taking the place of a temperature sensor, a typical plug would be much smaller, but you get the idea. Also worth noting, the thermostat housing may not be the only housing that serves as a hose-to-engine interface, often there is more than one housing that could easily be confused for a thermostat housing at a casual glance.

Excellent! I will look on the thermostat housing. I can get coolant in the exhaust manifold and heat exchanger but not into the thermostat housing, the pump, or any of the other circulating hoses.

[Endojoe]

I can get coolant in the exhaust manifold and heat exchanger but not into the thermostat housing, the pump, or any of the other circulating hoses.

Thats interesting. I'll have to ponder on that for a bit. I'm not really familiar with boat cooling systems, so this may be a somewhat odd question, but where do you fill the cooling system from? Because, it would seem logical to me that would be above (in terms of elevation) the water pump, so as to sort of force the pump to prime...

[mesquaukee]

The coolant filler is mounted on the header tank which usually has the heatexchanger in it, it may also be combined with the exhaust manifold. A hose at the bottom leads down to the pump.
That is what makes it so interesting. The hose connecting the header tank to the pump must drop down below the pump. The thermostat being closed will not let the air out so water cannot rise up to the pump. Opening up a connection as Endojoe suggests should do it, provided it is on the block side of the thermostat.

If such a hose is dropping down below the water pump you may consider if possible to reinstall it so water flows freely to the pump. Should you ever loose your coolant it would be easier to refill.

[GordMay]

As EndLoe & MesquaUkee say.
Whilst slowly filling, you might also squeeze the hoses, which sometimes helps move an air bubble (embolus) up and out the opening.

[donradcliffe]

If you have a hot water heater plumbed to the engine,it is one of the common causes of air lock. Pull the upper hose off where it attaches to the engine.

[Paul L]

Originally Posted by donradcliffe

If you have a hot water heater plumbed to the engine,it is one of the common causes of air lock. Pull the upper hose off where it attaches to the engine.

Second this suggestion.

Paul L

[captain58sailin]

Another possible source of trouble could be that one of your hoses is collapsing on the inside, shutting off your flow. Also if you have an expansion tank above your coolant reservoir try opening your coolant reservoir before starting the engine, just crack the cap until coolant comes out, then put some more coolant in your expansion tank, and start your engine.

[sneuman]

I should probably mention that I broke a belt that runs the internal coolant pump (i.e., NOT raw water) and briefly overheated the engine just before the trouble started. I assume they are related, as I lost coolant at the same time.

[NealS]

I had the same problem after replacing the freshwater (anti-freeze) pump on our Universal M-40 engine. I have a radiator style bleed valve on the top of the thermostat housing assemby that helps to get the air pocket out of the system. I removed the thermostat, added antifreeze, then attached the themostat housing back on. After I had topped off all the tanks, I then bleed the last air out from the themostat housing assemby.

[chala]

Some cooling systems have a “pump bypass drilling” which allows a minimal flow of coolant to circulate when the thermostat is in a closed position therefore air bleeding the system. If it applies to your system you may check that this drilling is not clogged.