Steam from coolant tank.

[Sam T]

Hi,

I have a bmc 1.8 which has recently started letting a little coolant and steam out of the coolant cap when it has been running for quite a long time.

 

I don't think it is a blown head gasket as doesn't have other main symptoms. Milky looking oil, bubles in coolant etc. I know this doesnt rule it out completely but want to be able to rule out other things before assuming it's an  expensive issue.

 

I fitted a new alternator belt, as was a little worn in case it was the pump not working properly.  After that, was able to run the engine (without moving the boat) for about an hour and a half with no issues so thought that had sorted it.

 

However after about 40 minutes

 cruising today it started to happen again.

 

On further inspection I found a minute leak (barely even a drip) in the coolant system which I have fixed (Just by tightening the connection on one of the hoses) and have run idle again for another half hour (while it was already hot from crusing) with no issues.

 

I'd read leaks could be a cause as let's air in which can lead to overheating so hoping this may have fixed it. But wondered if others may have further advice as to things I could look to diagnose/rule out.

 

If it happens again my next thought would be to try a new coolant tank cap.

 

It only seems to happen when cruising so need to move to diagnose whether various things have fixed it or not. As long as I keep an eye on it and don't let it keep running if it begins to happen again, I wondered if this posed any risk/further damage to the engine (realise that will depend largely on what the problem is)

 

The coolant level is the same as it has always been and the main engine temp thermometer has still never gone over its usual of around 70c.

 

If it persists I realise I'll have to get a mechanic in at some point as I'm no expert. But interested in people's thoughts as to whether there are any easy things I can mess around with myself first.

 

Thanks in advance!

Sam.

[Detling]

What about the washer gasket thing on the coolant cap if that has a flaw hot water vapour will come out and in cold weather be more noticeable.

[Sam T]

Thanks for the suggestion. There's no obvious flaw to it. I suppose it could be old and need replacing but doesn't feel brittle or obviously warn out.

[Grebe]

Assuming you are talking about the familar type of coolant/radiator ap, remeber that they have a set spring pressure.  This is a figure stamped into the metal top.  Replace like for like.  Changing the setting will adjust the boiling point of thr engine.

[Sam T]

Yes all standard as far as I'm aware. Provided it's not sorted and replacing the cap is my next step, will make sure I replace like with like. Thank you for pointing that out, that wasn't something I'd given thought to.

[Bee]

The engine will be working harder when it has a load on it so it will run much hotter than with no load. The thermostat will regulate this by opening more so it appears to run steadily at 70 C but temp gauges can be unreliable beasts as can their senders and I would guess that if you put your hand on the engine when its running in gear it could well feel hotter than out of gear even if it still says 70 C.  A bit more expansion could lead to a bit of water dribbling out of the overflow. If it was in a van you would never even know. I would just keep an eye on the gauge and after a year or two you will forget all about it.

[Chewbacka]

Just a thought, but have you topped up the coolant recently?  If you have overfilled, then when the engine gets hot the coolant expands and will slowly push the excess out of the cap.  When the engine cools the coolant will contract, and if you look in there will be a ‘gap’ between the coolant and the cap making it look high but not too much.  After a while at engine max temp, it will have expelled the excess and then should not overflow anymore.

[Sam T]

Thanks. Not very recently no. I flushed out the whole skin tank and put new water/antifreeze in within the last year, but would be very surprised if it'd been doing this for 8 months+ without me noticing, that said it's not impossible. 

 

Drove for another half hour this afternoon and had the same problem so the tiny leak wasn't the issue.

 

I don't need to move for another 2 weeks now, and my solar setup is sufficient that I don't really need the engine for electricity. So I think my plan may be to source a new cap within the next fortnight. Potentially also siphon out a little of the coolant to take it down maybe an inch in the tank rather than wait to see if it eventually chucks enough out.

 

If I still have the same issue when I next move after both those things I'll give it some more thought.

 

Bee, although your message is somewhat reassuring and I would love to just ignore it. I know for sure that this never used to happen,  and the fact that the engine is running hotter or in someway differently to how it did before makes me a bit uncomfortable.

 

Although I know a bit, I'm very much only an enthusiastic amateur, so forgetting about the fact that something different is happening makes me very nervous that I may be doing further internal damage somehow. Though nobody actually seems to be suggesting that this is the case which is a relief!

 

Thanks again.

[alan_fincher]

2 hours ago, Bee said:

The engine will be working harder when it has a load on it so it will run much hotter than with no load. The thermostat will regulate this by opening more so it appears to run steadily at 70 C but temp gauges can be unreliable beasts as can their senders and I would guess that if you put your hand on the engine when its running in gear it could well feel hotter than out of gear even if it still says 70 C.  A bit more expansion could lead to a bit of water dribbling out of the overflow. If it was in a van you would never even know. I would just keep an eye on the gauge and after a year or two you will forget all about it.

 

1 hour ago, Chewbacka said:

Just a thought, but have you topped up the coolant recently?  If you have overfilled, then when the engine gets hot the coolant expands and will slowly push the excess out of the cap.  When the engine cools the coolant will contract, and if you look in there will be a ‘gap’ between the coolant and the cap making it look high but not too much.  After a while at engine max temp, it will have expelled the excess and then should not overflow anymore.

But surely if it were expelling water at the filler cap simply because of overfilling and expansion, then that is all that would be happening - i.e. water would be dribbling out.

OP talks about steam - something that should not surely appear if the cooling circuit and thermostat are genuinely keeping the coolant to just 70 degrees?

I think the OP is correct and that something is at least slightly amiss, and that it is a new problem.  If all else is working as it should, I would not expect steam even if you ran it with the pressure cap completely removed.

[Sam T]

Ah yes, I hadn't clocked that the previous posts were only talking about liquid. There is definitely a small amount of steam coming off too.

 

Interested to hear if anyone had any further thoughts on diagnostic checks I could carry out.

 

If you wouldn't expect steam even with the pressure cap removed then I assume replacing the cap isn't going to solve the problem either......

[bizzard]

1 hour ago, Sam T said:

Ah yes, I hadn't clocked that the previous posts were only talking about liquid. There is definitely a small amount of steam coming off too.

 

Interested to hear if anyone had any further thoughts on diagnostic checks I could carry out.

 

If you wouldn't expect steam even with the pressure cap removed then I assume replacing the cap isn't going to solve the problem either......

The sniff test. Run the engine until hot, leave the filler cap off. While running put your hooter close to the filler and sniff, you might smell diesel exhaust. If so probably head gasket between a combustion chamber and water jacket.

[Sam T]

Ok thanks, can try that. When you say until hot, will it be sufficient to try in situe or will it need to be engaged in gear for that to happen?

As a slight aside. Was looking into sourcing a new cap too. The current one I have says ARH 1559 on it and I have no idea what this means. I was expecting to see a psi rating.

 

Any tips on what I should be looking for if I replace?

[AWETHEAYET]

Stick to the basics first, as suggested buy a new filler cap, run engine with this off untill air in system as migrated off then fit cap to pressurise, check for any leaks anywhere. Then report on here when the "experts" will advise if required.

 

[Chewbacka]

4 hours ago, alan_fincher said:

 

But surely if it were expelling water at the filler cap simply because of overfilling and expansion, then that is all that would be happening - i.e. water would be dribbling out.

OP talks about steam - something that should not surely appear if the cooling circuit and thermostat are genuinely keeping the coolant to just 70 degrees?

I think the OP is correct and that something is at least slightly amiss, and that it is a new problem.  If all else is working as it should, I would not expect steam even if you ran it with the pressure cap completely removed.

You won’t get actual steam at 70c but water at 70c especially in cold air will evaporate and look like a bit of steam.

[bizzard]

12 hours ago, Chewbacka said:

You won’t get actual steam at 70c but water at 70c especially in cold air will evaporate and look like a bit of steam.

Steam is invisible, but you'll know when you get it alright.

 

12 hours ago, Chewbacka said:

You won’t get actual steam at 70c but water at 70c especially in cold air will evaporate and look like a bit of steam.

 

[Boater Sam]

16 hours ago, Sam T said:

Ok thanks, can try that. When you say until hot, will it be sufficient to try in situe or will it need to be engaged in gear for that to happen?

As a slight aside. Was looking into sourcing a new cap too. The current one I have says ARH 1559 on it and I have no idea what this means. I was expecting to see a psi rating.

 

Any tips on what I should be looking for if I replace?

Most BMCs with exhaust manifolds with rubber end cap use 5 psi rad caps else the rubbers split very quickly.

[Machpoint005]

5 hours ago, bizzard said:

Steam is invisible, but you'll know when you get it alright.

 

 

 

If this had been a grammatical point, you would have been called a pedant.

As it is, you are quite simply correct (I'm thinking of buying a new "steam" floor cleaner but I've come to the conclusion that they should be called "hot-water cleaners". 

[Sam T]

5 hours ago, Boater Sam said:

Most BMCs with exhaust manifolds with rubber end cap use 5 psi rad caps else the rubbers split very quickly.

Thanks. Yes exhaust manifold with rubber end cap. Will order a 5 psi cap then. I assume if this does turn out to be any different to what it had on it before there's no harm to be done by having too low pressure?

20 hours ago, AWETHEAYET said:

Stick to the basics first, as suggested buy a new filler cap, run engine with this off untill air in system as migrated off then fit cap to pressurise, check for any leaks anywhere. Then report on here when the "experts" will advise if required.

 

Thank you, will do all of this and report back when I next take the boat for a cruise.

[Bee]

19 hours ago, Chewbacka said:

You won’t get actual steam at 70c but water at 70c especially in cold air will evaporate and look like a bit of steam.

This is true. Took my dog out for a walk this morning in the perishing cold, Dog had wonderful poo, well formed, good colour, firm and easy to pick up with poo bag and it lay there gently steaming. a) it was not boiling, and b) it doesn't steam in the summer.

[WotEver]

6 minutes ago, Bee said:

This is true. Took my dog out for a walk this morning in the perishing cold, Dog had wonderful poo, well formed, good colour, firm and easy to pick up with poo bag and it lay there gently steaming. a) it was not boiling, and b) it doesn't steam in the summer.

It makes a good hand warmer I’ve found...

[TheBiscuits]

5 hours ago, WotEver said:

It makes a good hand warmer I’ve found...

True, but by the time they are delivered your eBay customers complain they are cold, and don't react well to suggestions they stick them in the microwave for 20 seconds ...

[Boater Sam]

More pressure in the cooling system will just raise the boiling point, its fairly arbitrary on a boat as it should never get anywhere near  boiling in normal use.

At normal atmospheric pressure of 14.7 psi. one atmosphere, water boils at 99.98 degrees C, At +5 psi over atmospheric it will boil at 109 degrees C.

[BWM]

Air in the skin tank can cause problems or a failing water pump. 

[Sam T]

On 19/01/2020 at 13:33, Boater Sam said:

Most BMCs with exhaust manifolds with rubber end cap use 5 psi rad caps else the rubbers split very quickly.

Looking around online I'm struggling to find anything below 7psi. Would this be close enough to be good enough as far as not splitting the rubber goes. Don't want to cause more problems for myself.

 

Or any ideas where I could source a 5 psi?

 

Thanks.

On 20/01/2020 at 08:01, BWM said:

Air in the skin tank can cause problems or a failing water pump. 

Thanks, will be my next thing to look into if the cap doesn't sort it then.

 

If it was air in the skin tank I assume this could be sorted by loosening the connection on one of the skin tank pipes and running the engine for a bit before tightening back up? Hopefully not loosing too much coolant into the engine bay in the process....

[bizzard]

33 minutes ago, Sam T said:

Looking around online I'm struggling to find anything below 7psi. Would this be close enough to be good enough as far as not splitting the rubber goes. Don't want to cause more problems for myself.

 

Or any ideas where I could source a 5 psi?

 

Thanks.

Thanks, will be my next thing to look into if the cap doesn't sort it then.

 

If it was air in the skin tank I assume this could be sorted by loosening the connection on one of the skin tank pipes and running the engine for a bit before tightening back up? Hopefully not loosing too much coolant into the engine bay in the process....

Yes with the filler cap on. And if air does come out of course you then need to top up.

Edited January 22, 2020 by bizzard