Blown head gasket (again!)

[IdealStandard]

I need some help here diagnosing what must be an underlying issue with my engine. It's a Shanks 35 installed in 2010, that is all I know about it as the previous owner is now deceased.

 

Around a month ago I diagnosed a blown head gasket and engine breathing. I employed a local mechanic and together we stripped the head, changed the gasket and had the head skimmed (it was warped). This solved both problems and I was a happy boater. At the same time I changed both of the thermostats (twin thermostat system) which both looked knackered and was confident I was ready to go.

 

I have done plenty of cruising since then (Oxford to Bristol) and everything worked fine apart from one thing. Occasionally the coolant system would do funny things, like seem to be under incredible pressure even long after the engine was off, at one point the header tank was completely full of water and when I opened the lid it all bubbbled back into the system. It also went down a couple of times, but I attributed this to leaks when putting the engine back together (I found one and stopped it). I also religiously bled the coolant system when I topped up the header tank - open engine filler tap, run for several minutes, close filler cap, carry on - and for the most part the cooling system seemed to be doing it's job and was getting hot in all the right places.

 

Two days ago I fired up the engine to charge the batteries (my starter motor had been off for 10 days so needed a good charge). I topped up the water and bled the engine and checked the oil, everything looked fine. After about an hour or so I checked under the deck boards and the engine was steaming. Bollocks! I felt the coolant tubes and they were cold! Bollocks! I opened the header tank cap and suddenly the coolant system kicked in, but it was too late! When I did my checks the next day there were specks of water in the oil and on the rocker cover case cap.

 

Changing the head gasket again isn't the end of the world. I'm not going to do it straight away, but can do it myself for the price of the parts.

 

So.........

 

What am I missing? What's wrong here?

 

My diagnosis would be some kind of airlock or trapped air in the system, but if I ran the engine with the filler cap open it should have dissipated any air.

 

I have also ordered a new header tank cap, because it could have been failing to release excess pressure, but again I don't understand how the coolant system failed to work from cold with new thermostats!!

 

Many thanks in advance

Tim (The unluckiest boater)

[LEO]

Not sure if you still have to do it on modern engines, but did you re-tighten the C./nuts after running the engine for a few hours.

 

Had this problem with a BMC 1.5 I had.

 

L.

[MtB]

I need some help here diagnosing what must be an underlying issue with my engine. It's a Shanks 35 installed in 2010, that is all I know about it as the previous owner is now deceased.

 

Around a month ago I diagnosed a blown head gasket and engine breathing. I employed a local mechanic and together we stripped the head, changed the gasket and had the head skimmed (it was warped). This solved both problems and I was a happy boater. At the same time I changed both of the thermostats (twin thermostat system) which both looked knackered and was confident I was ready to go.

 

I have done plenty of cruising since then (Oxford to Bristol) and everything worked fine apart from one thing. Occasionally the coolant system would do funny things, like seem to be under incredible pressure even long after the engine was off, at one point the header tank was completely full of water and when I opened the lid it all bubbbled back into the system. It also went down a couple of times, but I attributed this to leaks when putting the engine back together (I found one and stopped it). I also religiously bled the coolant system when I topped up the header tank - open engine filler tap, run for several minutes, close filler cap, carry on - and for the most part the cooling system seemed to be doing it's job and was getting hot in all the right places.

 

Two days ago I fired up the engine to charge the batteries (my starter motor had been off for 10 days so needed a good charge). I topped up the water and bled the engine and checked the oil, everything looked fine. After about an hour or so I checked under the deck boards and the engine was steaming. Bollocks! I felt the coolant tubes and they were cold! Bollocks! I opened the header tank cap and suddenly the coolant system kicked in, but it was too late! When I did my checks the next day there were specks of water in the oil and on the rocker cover case cap.

 

Changing the head gasket again isn't the end of the world. I'm not going to do it straight away, but can do it myself for the price of the parts.

 

So.........

 

What am I missing? What's wrong here?

 

My diagnosis would be some kind of airlock or trapped air in the system, but if I ran the engine with the filler cap open it should have dissipated any air.

 

I have also ordered a new header tank cap, because it could have been failing to release excess pressure, but again I don't understand how the coolant system failed to work from cold with new thermostats!!

 

Many thanks in advance

Tim (The unluckiest boater)

Being a fault tracer by trade, my personal maxim has become "Assumption is the mother of all cock-ups". It would appear from your story that the head gasket may not have been the problem in the first place. The symptoms of head gasket failure can be caused by other things too, and I wonder if you (or your mechanic) assumed head gasket failure simply it is the most common cause of those symptoms.

 

What was the old head gasket like when you removed it? Did you inspect it with great care to satisfy yourself it had failed, or just chuck it in the bin? It is perfectly possible that the distorted head which you have machined flat is actually cracked inside. It's also possible, but less likely, that there is a crack in the cylinder block. I'd say the enxt step is to remove the head and carefully inspect the gasket to see if it shows evidence of leaking from a waterway across to an oilway. If there is no evidence, time to get the head waterways pressure tested, I'd suggest.

 

Others here know more about engines than me though. The may be something more obvious.

 

MtB

[IdealStandard]

Not sure if you still have to do it on modern engines, but did you re-tighten the C./nuts after running the engine for a few hours.

 

Had this problem with a BMC 1.5 I had.

 

L.

 

 

That was something which occured to me, but the design of the head means that you'd have to remove the rockers and redo all of the valve clearance adjustments. Maybe I should have done it.

[MtB]

[Duplicate post edited out]

Edited December 6, 2012 by Mike the Boilerman

[IdealStandard]

Being a fault tracer by trade, my personal maxim has become "Assumption is the mother of all cock-ups". It would appear from your story that the head gasket may not have been the problem in the first place. The symptoms of head gasket failure can be caused by other things too, and I wonder if you (or your mechanic) assumed head gasket failure simply it is the most common cause of those symptoms.

 

What was the old head gasket like when you removed it? Did you inspect it with great care to satisfy yourself it had failed, or just chuck it in the bin? It is perfectly possible that the distorted head which you have machined flat is actually cracked inside. It's also possible, but less likely, that there is a crack in the cylinder block. I'd say the enxt step is to remove the head and carefully inspect the gasket to see if it shows evidence of leaking from a waterway across to an oilway. If there is no evidence, time to get the head waterways pressure tested, I'd suggest.

 

Others here know more about engines than me though. The may be something more obvious.

 

MtB

 

You could well be right.

 

I still have the old gasket and will re-inspect. We thought there was a small failure, but were suitably dubious.

[steamraiser2]

I would suspect that you have a crack, either in the head or the block itself. A system pressure test would be a good start. If a test does not expose a leak you may care to consider air locking in the cooling system. This can result in localised overheating which can contribute to head gasket failure.My money is on a crack.

[MtB]

That was something which occured to me, but the design of the head means that you'd have to remove the rockers and redo all of the valve clearance adjustments. Maybe I should have done it.

The engine service manual will give you information like this. I'd suggest you obtain one and check to see what it says on this point.

 

MtB

[IdealStandard]

The engine service manual will give you information like this. I'd suggest you obtain one and check to see what it says on this point.

 

MtB

 

I have the manual. It doesn't mention retightening the bolts. We torqued them up to the correct levels and in the correct order.

[Yamanx]

Sounds daft, but if the thermostats were fitted the wrong way around, ie: the lower temp one in place of the higher and visa versa, this might provide the symptoms you have been having.

[Tony Brooks]

 

snip

 

Two days ago I fired up the engine to charge the batteries (my starter motor had been off for 10 days so needed a good charge). I topped up the water and bled the engine and checked the oil, everything looked fine. After about an hour or so I checked under the deck boards and the engine was steaming. Bollocks! I felt the coolant tubes and they were cold! Bollocks! I opened the header tank cap and suddenly the coolant system kicked in, but it was too late! When I did my checks the next day there were specks of water in the oil and on the rocker cover case cap.

 

Changing the head gasket again isn't the end of the world. I'm not going to do it straight away, but can do it myself for the price of the parts.

 

So.........

 

What am I missing? What's wrong here?

 

My diagnosis would be some kind of airlock or trapped air in the system, but if I ran the engine with the filler cap open it should have dissipated any air.

 

I have also ordered a new header tank cap, because it could have been failing to release excess pressure, but again I don't understand how the coolant system failed to work from cold with new thermostats!!

 

Many thanks in advance

Tim (The unluckiest boater)

 

 

I would EXPECT to find condensation inside a cold engine at this time of year unless it was in a warm engine room so I am not convinced that you actually have a head gasket problem based on what you tell us.

 

As far as airlocks are concerned much depends upon how the cooling pipes/hoses have been run. Many boats with upward or downward half loops in their hoses require manual manipulation of the said hoses to allow the air to escape.

 

There is no way in which I can see a pressure cap remaining closed when it should open unless you glued the rubber seal to the filler neck. If it tried a hose would have blown off or blown up like a balloon. The most common problems with caps are the rubber seals deteriorating so the do not seal, the springs becoming weak over time or the vacuum valve sticking closed but that would not have a major effect on a boat engine because you do not have a radiator to collapse.

 

My advice is to give it a good hard run to see if the water droplets are worse or the oil develops a whitish hue and to see if it overheats.

 

As Mike says - do not make assumptions.

[simon&jan]

Have seen someone fit a thermostat upside down , gave the same symptoms ??

[IdealStandard]

Sounds daft, but if the thermostats were fitted the wrong way around, ie: the lower temp one in place of the higher and visa versa, this might provide the symptoms you have been having.

 

 

Not daft at all, but I don't understand how it would cause the symptoms described.

 

The twin thermostats are 75C at the bottom (domestic) and 80C on top (skin tank). I would say that I am pretty sure I got them the right way around but am the first to admit my infallibility.

 

My thinking would be that if they were the wrong way round, there would be no engine cooling until 80C and then both would open. 80C isn't an unreasonable engine temperature.

[IdealStandard]

double post

Edited December 6, 2012 by IdealStandard

[RLWP]

<snip>

 

My diagnosis would be some kind of airlock or trapped air in the system, but if I ran the engine with the filler cap open it should have dissipated any air.

 

<snip>

 

Tim (The unluckiest boater)

 

I agree with your diagnosis, I disagree with your assumption that your cooling system is self-bleeding. Most canal boat cooling systems are lash-ups and can have all kinds of places that air can linger

 

Check your skin tanks for air bleed points

 

Richard

[IdealStandard]

I would EXPECT to find condensation inside a cold engine at this time of year unless it was in a warm engine room so I am not convinced that you actually have a head gasket problem based on what you tell us.

 

As far as airlocks are concerned much depends upon how the cooling pipes/hoses have been run. Many boats with upward or downward half loops in their hoses require manual manipulation of the said hoses to allow the air to escape.

 

There is no way in which I can see a pressure cap remaining closed when it should open unless you glued the rubber seal to the filler neck. If it tried a hose would have blown off or blown up like a balloon. The most common problems with caps are the rubber seals deteriorating so the do not seal, the springs becoming weak over time or the vacuum valve sticking closed but that would not have a major effect on a boat engine because you do not have a radiator to collapse.

 

My advice is to give it a good hard run to see if the water droplets are worse or the oil develops a whitish hue and to see if it overheats.

 

As Mike says - do not make assumptions.

 

I'm not planning to do anything about the problem other than keep an eye for a little while anyway and will do as you say. However I am pretty sure there's enough water to suggest a problem. I wiped clean the rocker cover cap and ran the engine, it had droplets covering the entire surface within five minutes.

 

I see your point about the pressure cap, but why do you think the cooling system suddenly kicked in when I removed the cap?

 

Next thing is to keep a very close eye on the coolant and try to gauge the quantity of water going down.

[Tony Brooks]

I'm not planning to do anything about the problem other than keep an eye for a little while anyway and will do as you say. However I am pretty sure there's enough water to suggest a problem. I wiped clean the rocker cover cap and ran the engine, it had droplets covering the entire surface within five minutes.

 

I see your point about the pressure cap, but why do you think the cooling system suddenly kicked in when I removed the cap?

 

Next thing is to keep a very close eye on the coolant and try to gauge the quantity of water going down.

 

 

No idea without seeing and possibly testing the boat but you may have released an airlock that did not have enough pressure to open the cap.

[RobinJ]

I'm not planning to do anything about the problem other than keep an eye for a little while anyway and will do as you say. However I am pretty sure there's enough water to suggest a problem. I wiped clean the rocker cover cap and ran the engine, it had droplets covering the entire surface within five minutes.

 

I see your point about the pressure cap, but why do you think the cooling system suddenly kicked in when I removed the cap?

 

Next thing is to keep a very close eye on the coolant and try to gauge the quantity of water going down.

A few things.

When you fill up, do you fill to the lower mark?

Excess pressure may cause the coolant to blow the weakest point (and that may be the head gasket)!

You imply you have a calorifier (or heating circuit), this could also hold an air lock. This can be a problem if the engine is not truely level and/or the coolant circuits have kinks and bends in them. Problem you have with 2 thermostats is, it will have to get up to full temeprature to let all the air past each one!

Other option would be to do a compression test to see if one cylinder has lost some!

Cracked head or cylinder normally show up with exhaust steam or milky oil very quickly, but at this time of year maybe not as easy to see.

[IdealStandard]

A few things.

When you fill up, do you fill to the lower mark?

yes

 

Excess pressure may cause the coolant to blow the weakest point (and that may be the head gasket)!

You imply you have a calorifier (or heating circuit), this could also hold an air lock. This can be a problem if the engine is not truely level and/or the coolant circuits have kinks and bends in them. Problem you have with 2 thermostats is, it will have to get up to full temeprature to let all the air past each one!

 

Good point, so the engine should be run with the engine filler open until both thermostats have opened to even start bleeding the coolant!

 

The domestic heating system is currently on theoretical, there is a pipe which would head to a calorifier, but not currently.

 

 

Cracked head or cylinder normally show up with exhaust steam or milky oil very quickly, but at this time of year maybe not as easy to see.

 

 

I have never had a single puff of untoward smoke.

[Iain_S]

(snip) Problem you have with 2 thermostats is, it will have to get up to full temeprature to let all the air past each one!

(snip)

 

I saw this problem fixed once by drilling a small hole through both thermostats to allow the air to bleed. IIRC, thermostats used to come with the hole already drilled, and a giggle pin fitted to stop said hole getting blocked.

 

Iain

[Krusty]

Did you change the cyinder head bolts?

 

Later engines now have pre-stretched bolts to avoid the need to re-torque.

Re-tightening old bolts (if the heads don't snap off), may not give you the correct torque settings.

I know this because it happened to me when my gasket went.

[ROBDEN]

Did you change the cyinder head bolts?

 

Later engines now have pre-stretched bolts to avoid the need to re-torque.

Re-tightening old bolts (if the heads don't snap off), may not give you the correct torque settings.

I know this because it happened to me when my gasket went.

I concur with Krusty.

My vetus gasket went, replaced using the same bolts, went again.

Even had the strange things with the water, header tank filling and the pressure still there the next morning.

 

Asked Vetus, they said about the bolts.

Used new bolts and no more trouble. Over 6 months now.

Good luck.

[n.b.Goldie]

Did you change the cyinder head bolts?

 

Later engines now have pre-stretched bolts to avoid the need to re-torque.

Re-tightening old bolts (if the heads don't snap off), may not give you the correct torque settings.

I know this because it happened to me when my gasket went.

 

Please excuse my lack of knowledge but what is the difference between a 'pre-stretched' bolt and an old (non-pre-stretched) bolt? Surely the old bolt was stretched in first use and would thence be 'pre-stretched'.

 

Or is it just good practice to use new bolts each time the head is removed on the basis that it might not be known what type of bolt it is and how many times it has been removed and re-used.

 

Perhaps I have just answered my own question but please reply if I have mis-understood.

 

 

Thanks

Ditchdabbler

 

 

 

[LEO]

That was something which occured to me, but the design of the head means that you'd have to remove the rockers and redo all of the valve clearance adjustments. Maybe I should have done it.

 

It is the same convuluted arrangement on the 1.5, but it is made easier by ownership of a special spanner - got one and re-torquing the nuts became much easier/.

 

m

[rrt2]

Please excuse my lack of knowledge but what is the difference between a 'pre-stretched' bolt and an old (non-pre-stretched) bolt? Surely the old bolt was stretched in first use and would thence be 'pre-stretched'.

 

Or is it just good practice to use new bolts each time the head is removed on the basis that it might not be known what type of bolt it is and how many times it has been removed and re-used.

 

Perhaps I have just answered my own question but please reply if I have mis-understood.

 

 

Thanks

Ditchdabbler

 

The new bolt is not pre-stretcted until you fit it and tighten it up it then stretches. These came into use when due to the use of more slippery greases being used on nuts and bolts torque reading became unrealiable.