Airlock Isuzu 55

[blackrose]

Mine is the earlier 4LE1

[blackrose]

Here's a picture of the new thermostat on the left compared to the old one on the right. 

 

Just done some measurements with my Vernier. The big flange at the top is the same diameter (54mm) The smaller sprung flange at the bottom is 28mm on the old thermostat and 29mm on the new one. The overall height of the thermostats between top and sprung flanges is 30.7mm on the old thermostat and 30mm on the new one and the sprung movement on the old unit is only 5mm while on the new one it's about 9.5mm. The tops of the thermostats look different. Is that a rubber sealing ring on the old thermostat?

 

 

I can't tell if they're working in boiling water or not?

Edited April 13, 2023 by blackrose

[Tony Brooks]

Yes, it could. There is a "hole" in the casing in the bottom of the thermostat housing that communicates with the water pump inlet. When the engine is cold, this hole is typically open, so coolant from the engine can be circulated through the engine only. This helps to stop hot spots inside the head overheating and furring up.

 

When the thermostat opens, the bottom flange seals that hole, directing coolant to the skin tank. However, if the gap between the thermostat flange and the bottom of the housing is too great the hole will not seal, so coolant can bypass the skin tank, but why your engine did not run hotter than normal I have no idea.

 

Assuming the calorifier take off is from the engine (head) side of the thermostat, there will be less available "pressure" to persuade then coolant to flow through the calorifier.

 

[blackrose]

Ok thanks. Looks like an expensive OEM thermostat may be the only solution.

[Mike Adams]

I have just pulled the thermostat from my spare(almost new) engine in the workshop which I  am sure is factory. Hope this helps. It has a rubber seal at the top. You should see the top open in boiling water or heat it up slowly in a saucepan and you should see it open before the water boils. You can see the quality of the jap oem stat they almost never fail in my experience

[blackrose]

Thanks. Mine is 18 years old and I think it has failed.

 

I've just ordered an equivalent thermostat from these people. It's not genuine Isuzu but then I don't think Engines Plus supply genuine Isuzu either? I spoke to Engines Plus this morning and they were talking about Canal line engines and I just got confused.

 

Thermostat 3LD1 8972112090 option 2 - Plant Spares Online

 

On their website it's shown as 3LD1 but option 2 is for the 4LE1 (their website needs updating but it's a 54mm 82C thermostat and the guy said Option 2 is suitable for the 4LE1)

 

£32.50 + VAT (rather than £54 + VAT from Engines Plus)

Edited April 14, 2023 by blackrose

[blackrose]

Fitted the new thermostat this afternoon and all seems well. The calorifier is now getting hot. Coolant is still not expanding into the bottle via the reservoir cap but perhaps it just needs filling up a bit more or possibly it needs a proper run to do that.

 

The new thermostat isn't exactly the same as the original - is has no visible rubber seal at the top for example but all the dimensions seem the same. 

[Tracy D'arth]

So was it a duff stat or just one that didn't fit?

[blackrose]

5 hours ago, Tracy D'arth said:

So was it a duff stat or just one that didn't fit?

 

The 18 year old original one stopped working and the second one I replaced it with looked ok and was more or less the right dimensions but didn't work. I was trying to avoid paying about £89 for an original. The one I've just fitted was about £37

[blackrose]

There's still something wrong somewhere.

 

I loosened the coolant reservoir filler cap today. The engine was stone cold but the reservoir was full of air pressure after being run yesterday. 

 

I don't understand it. I've bled both skin tanks and there was no air in either of them. I'm pretty sure the new thermostat is working as one of the skin tanks was getting hot yesterday.

 

I'm afraid this one's stumped me completely.

Edited April 20, 2023 by blackrose

[blackrose]

So coming back to this, everything on the engine heating/cooling system is working fine. The engine stays at 80C even when I push it hard, both skin tanks get warm, calorifier is now getting hot, so the thermostat must be working. 

 

However, the antifreeze/coolant is not expanding through the filler cap drain tube into the external bottle. I disconnected the hose from the bottle and let it hang down from the filler cap drain into the bilges but nothing is coming out as it used to. I blew down the hose to check it wasn't blocked.

 

Ran the engine up to temperature again but no coolant coming out of the coolant cap drain hose. The next day with the engine stone cold there was still a lot of pressure contained in the engine coolant reservoir which is released when the coolant cap is slowly undone. To me this indicates that the coolant pressure cap isn't working. But it's a new cap which I bought recently to try to solve this issue - neither new or old cap work.

 

Can anyone think of a reason why the coolant pressure cap isn't working?

[Tony Brooks]

Where is this cap? On the exhaust manifold cum header tank or on a separate remote header tank. If the latter, what is on the filler on the manifold?

 

Things that come to mind:

 

A long fuller neck cap that someone has managed to fit on a short filler neck.

 

All filler caps are plain caps with a sealing washer under the cap.

 

For some reason, the water expansion is not enough to lift the pressure cap off its seat.

 

To be honest, it makes little sense to me, but I recall someone here saying it indicated a faulty head gasket, but I did not understand why then and still don't.

[Tracy D'arth]

It sounds to me as being perfectly normal. There will be a small pocket of air somewhere, possibly in a corner of a skin tank. Its normal.

You will not get a hot discharge from the cap/expansion tube unless the system is overfilled when cold.

[Iain_S]

11 hours ago, blackrose said:

So coming back to this, everything on the engine heating/cooling system is working fine. The engine stays at 80C even when I push it hard, both skin tanks get warm, calorifier is now getting hot, so the thermostat must be working. 

 

However, the antifreeze/coolant is not expanding through the filler cap drain tube into the external bottle. I disconnected the hose from the bottle and let it hang down from the filler cap drain into the bilges but nothing is coming out as it used to. I blew down the hose to check it wasn't blocked.

 

Ran the engine up to temperature again but no coolant coming out of the coolant cap drain hose. The next day with the engine stone cold there was still a lot of pressure contained in the engine coolant reservoir which is released when the coolant cap is slowly undone. To me this indicates that the coolant pressure cap isn't working. But it's a new cap which I bought recently to try to solve this issue - neither new or old cap work.

 

Can anyone think of a reason why the coolant pressure cap isn't working?

I recall an engine, not sure if it was an Isuzu, where the cure for a similar problem was to drill a small hole in the thermostat. air gathered under it, and, with no giggle pin, stayed there, The thermostat didn't get hot enough to open, although the engine got hot enough to boil over.

[blackrose]

15 hours ago, Tony Brooks said:

Where is this cap? On the exhaust manifold cum header tank or on a separate remote header tank. If the latter, what is on the filler on the manifold?

 

The pressure cap is on the engine coolant reservoir/header tank.

 

12 hours ago, Tracy D'arth said:

It sounds to me as being perfectly normal. There will be a small pocket of air somewhere, possibly in a corner of a skin tank. Its normal.

You will not get a hot discharge from the cap/expansion tube unless the system is overfilled when cold.

 

Both skin tanks have been bled. The air pocket isn't in the skin tanks it's in the engine header tank.

 

I don't think it's perfectly normal for the coolant filler cap not to work when its set pressure point is reached. Now I haven't actually measured the pressure in the header tank but it seems obvious to me that if so much pressure is in there when the engine is cold. It must have been a lot more when the engine was hot.

 

I can fill the engine coolant expansion tank right up to the top and the coolant still won't expand out when the engine is hot. It used to expand and come out the overflow tube under the pressure cap so don't think what's happening now is normal..

4 hours ago, Iain_S said:

I recall an engine, not sure if it was an Isuzu, where the cure for a similar problem was to drill a small hole in the thermostat. air gathered under it, and, with no giggle pin, stayed there, The thermostat didn't get hot enough to open, although the engine got hot enough to boil over.

 

But as I explained, the thermostat is working. Both skin tanks are getting hot.

15 hours ago, Tony Brooks said:

To be honest, it makes little sense to me, but I recall someone here saying it indicated a faulty head gasket, but I did not understand why then and still don't.

 

It makes no sense to me either. I'll check the oil for any signs of water, but the engine seems to run normally.

Edited April 28, 2023 by blackrose

[Tracy D'arth]

OK, you think it is wrong.

[Tony Brooks]

4 hours ago, blackrose said:

can fill the engine coolant expansion tank right up to the top and the coolant still won't expand out when the engine is hot. It used to expand and come out the overflow tube under the pressure cap so don't think what's happening now is normal.

 

That suggests there is a large air pocket somewhere that acts as an expansion vessel when the coolant is heated so the pressure rise in the system is less than normal, but where or how I have no idea.

 

I note that you say skin tanks (plural). That may well make getting a large air pocket in the "cool" tank easier.

[Mike Adams]

I would say everything is fine. Mine holds a bit of pressure even a couple of weeks after it has been run which wouldn’t happen if it had a leak or a head gasket problem.

[blackrose]

15 hours ago, Tony Brooks said:

 

That suggests there is a large air pocket somewhere that acts as an expansion vessel when the coolant is heated so the pressure rise in the system is less than normal, but where or how I have no idea.

 

I note that you say skin tanks (plural). That may well make getting a large air pocket in the "cool" tank easier.

 

Yes, there could be an air pocket somewhere that's being compressed and accommodating the coolant expansion. 

5 hours ago, Mike Adams said:

I would say everything is fine. Mine holds a bit of pressure even a couple of weeks after it has been run which wouldn’t happen if it had a leak or a head gasket problem.

 

Ok, but in that case why has the behaviour of the cooling system changed? As I said, coolant used to expand and get forced out of the hose under the pressure cap, now it doesn't. 

 

I'll take it out for a run up the river this weekend. 

[Tracy D'arth]

After a few weeks running, any air pocket will get absorbed and expelled then you will find that if you overfill the expansion/heat exchanger it will expel the excess via the cap/overflow pipe.

[blackrose]

Perhaps you're all right. I took the boat down the river for 3 hours yesterday and came back to my mooring today. The engine is staying at 80C even when pushed hard upstream, although I only has the chance to push it hard for short periods. 

 

Anyway, my neighbour came up with an interesting theory. He thinks that perhaps the old coolant filler pressure cap was never working properly and releasing coolant through the overflow too easily and then eventually it stopped working causing over-pressurisation of the system. Then when I replaced the pressure cap it's doing what it should do and not activating so easily causing a normal pressure build up in the system. 

 

I'll just leave it for now as the engine seems ok and isn't overheating. I checked the oil and there's no water in it.

[Tony Brooks]

6 minutes ago, blackrose said:

Perhaps you're all right. I took the boat down the river for 3 hours yesterday and came back to my mooring today. The engine is staying at 80C even when pushed hard upstream, although I only has the chance to push it hard for short periods. 

 

Anyway, my neighbour came up with an interesting theory. He thinks that perhaps the old coolant filler pressure cap was never working properly and releasing coolant through the overflow too easily and then eventually it stopped working causing over-pressurisation of the system. Then when I replaced the pressure cap it's doing what it should do and not activating so easily causing a normal pressure build up in the system. 

 

I'll just leave it for now as the engine seems ok and isn't overheating. I checked the oil and there's no water in it.

 

I think that is very unlikely. Apart from the expansion space above the coolant in the header tank you have an enclosed system so as the coolant expands it will compress the air above the coolant. Only if this space is not large enough will it expel coolant. The amount expelled depends upon the system volume, which is a more or less constant, the air space for expansion, and the temperature rise. Now all those will be more or less the same, The strength of the pressure cap spring really can't affect any of those except in very rare circumstances when under high speed and load. No spring, a light spring, or a strong spring, the volume expelled will be the same.

 

So why ado/did you see what you did. there are two possibilities.

 

1. Originally there was something that caused a greater expansion and this could be air because AIUI air expands to a greater extent than coolant when heated to the same temperature.

 

2. Something is now allowing the coolant space to expand into rather than blowing it out of the cap.

 

As this is a twin tank system, I think trapped air, not necessarily in a tank, would explain both possibilities. 1 would need the air to be trapped in a hot part of the system, and 2 would need it trapped in a cooler part. none of this makes me believe that you did not bleed it, the air, if there was any, did not shift to a bleed point.

 

The reason we pressurise the system is to do with preventing localised boiling inside the engine on certain internal hot spots (exhaust valve seats & injector bosses). This is very unlikely to occur in a canal boat engine unless run very hard for a long period on rivers. It really has nothing to do with keeping coolant in the engine at all (except coolant will be expelled if localised boiling takes place).

[blackrose]

Ok, so perhaps there is air in the system somewhere but it doesn't seem to be affecting engine cooling. Hopefully it will work its way out eventually.

[Tony Brooks]

Just now, blackrose said:

Ok, so perhaps there is air in the system somewhere but it doesn't seem to be affecting engine cooling. Hopefully it will work its way out eventually.

 

Either work It's way out or get absorbed in the water. With twin tanks (no dimensions & HP), I suspect that you have excess cooling capacity, so even if air does reduce the cooling ability, it won't make any difference.

 

Note for new boaters: excess cooling capacity is not a problem, the engine thermostat keeps the engine at the optimum temperature.

[David Mack]

33 minutes ago, Tony Brooks said:

With twin tanks (no dimensions & HP), I suspect that you have excess cooling capacity,

I seem to recall @blackrose added the second skin tank because he had insufficient cooling capacity.