Where's my coolant gone?

[alhendo1 3,031]

Hi folks....this is a CB500x question which hopefully you won't mind me asking on the NC forum...I know there are a few CB500 owners past and present.....I returned from the North Coast 767 last night....actually it ended up the NC 970 or something like that....I was cleaning the bike down and noticed my coolant expansion tank was almost empty bar a tiny drop at the bottom....it was slightly over full before I left at just over 1000 miles.....I had a look online last night and found a thread where it suggested that air in the coolant is forced out the system at higher rpm as it is filled cold from the factory and there will be air in the system. ..or something like that. ...there's no trace of any leak from waterpump/weephole...radiator/hoses....it's just disappeared. ...any ideas or has this happened to any other cb owners 😨

[Andy m 23,473]

No idea, but I'm going to check mine.

 

I'd give it until morning to settle down then think about topping it up. The idea a good high RPM run will find the nooks and crannies makes sense. The only place it can go is out through a hole or out through the breather. If you had it hot it can cook off, but IMHO would still leave marks.

 

I've heard the oil can drop suddenly at a couple of thousand miles as some passage the factory can accidentally close with grease will open, but nothing on the coolant.

 

Andy

[Andy m 23,473]

Right, at 1100 miles, mine is between the lines.

 

Interestingly, the nice chaps at Padgetts drew a line in marker and dated it. One wonders if that's because they know something?

 

They've gone up in my opinion anyway.

 

Andy

[Tex 36,816]

I would simply top it up (when cold) with the correct coolant and then keep an eye on it for a week or two. I’m sure there’s nothing sinister about it. Fluids/oils need topping up sometimes, end of story.

 

Of course if you top it up and the level drops again that’s a different story. 

[Grumpy old man 4,670]

Check it's got a head gasket ( there was a NC that didn't have a Head gasket from new) I'm sure it has, I'm just being silly.

[Reckless 945]

Make sure the radiator is filled too, the expansion tank takes what is forced out of the system, then when everything cools it gets sucked back into the system, with the expansion bottle, being very low it could suggest it’s sucked back in as much as it could but perhaps not enough

[alhendo1 3,031]

56 minutes ago, Andy m said:

Right, at 1100 miles, mine is between the lines.

 

Interestingly, the nice chaps at Padgetts drew a line in marker and dated it. One wonders if that's because they know something?

 

They've gone up in my opinion anyway.

 

Andy

Yup....they've drawn a line on mine at where it wouldbe at the upper mark on the sidestand....there is also some writing on mine as well ...how odd....

[alhendo1 3,031]

Update...I've just run it till the fan came on and switched it off and almost instantly the expansion tank started filling up again....I thought I'd found a leak but I reckon it's a false alarm...there's a thick rubber protective shroud around the bottom rad hose where it touches the front of the engine...water came tricking out there when it got hot but a quick taste revealed it's not coolant....I think it's water which was stuck in there from washing it yesterday and the heat forced it out. ...I squeezed a few hoses as well while it was warming up....maybe there's air in the system somewhere....I'll pop up to the dealers on Tuesday when the workshop folk are in and run the scenario by them.....thanks for the replies folks👍

[embee 7,288]

3 hours ago, Reckless said:

Make sure the radiator is filled too, the expansion tank takes what is forced out of the system, then when everything cools it gets sucked back into the system, with the expansion bottle, being very low it could suggest it’s sucked back in as much as it could but perhaps not enough

What Reckless says.

You must start with the engine/rad system filled completely. The expansion (or make-up) bottle is there to allow coolant to come out of the filled system when it heats and expands, and then gets drawn back in when it cools. If the system isn't filled properly initially it will draw back coolant from the bottle and potentially empty it.

The bottle filling after shut down is due to "after-boil" when the circulation stops and coolant boils locally at the hot spots (exhaust ports etc). This really shouldn't happen except under extreme circumstances like pulling off a motorway and immediately stopping the engine. At idle there shouldn't be any area hot enough to cause this, the fan comes on simply because there's no air movement, not because any metal parts are overly hot. At idle there's very little heat to coolant from the engine, no large amounts of fuel being burnt, and at a bulk coolant temp of around 106C or so the fan should come on, whereas the boiling point of 50/50 ethylene glycol/water at 1Bar cap pressure is more like 125C (give or take) so after-boil should be minimal or non existant.

The dealers marking the bottles is somewhat suspicious however ...................... I wonder if the rad caps are set at too low pressure? They're usually around 1Bar, normally marked on the cap. Would be ideal is someone could check the rad cap valve opening pressure and see if it's really what it says on the tin.

Edited June 24, 2018 by embee

[alhendo1 3,031]

That's the bike dropped off at the dealers...the techie said he'll check it over etc.....I'll keep you all posted....thanks for the replies.

[alhendo1 3,031]

Forgot to say expansion tank was empty this morning hence the visit to the dealer....

[alhendo1 3,031]

Well its back now...techie said he'd checked there was coolant in the radiator and had confirmed that although it didn't get stone cold he did notice the level dropping although it didn't disappear totally....no sign of any other leaks...it's now been topped up to the upper level so I'll see where it is in the morning....

[larryblag 14,236]

Good luck with this. Let us know, it does sound a bit odd. 

[alhendo1 3,031]

Thanks. Checked this morning and its sitting just below the upper level...I'll keep an eye on it...didn't have the bike out today so I'll give it a run tomorrow then check it again when it's cold.

[alhendo1 3,031]

I checked this morning and it was still at roughly the same level....just back from a 430 mile run in this hot weather we're experiencing....I'll recheck in the morning. ...here's hoping it's just been air in the system from factory filling....someone on the CB500 forum had a similar issue at 1000 miles and just neede a top up.

[kharli 100]

For nc owners I have noticed if the fan starts to cut in earlier than you have previously noticed , it could be a sign of low water in the radiator.

I had an intermittent leak from water pump , My expansion tank after 6 and a half years was surprisingly full of white and black flakes .I flushed the whole system best I could with hose then flushed through with distilled water ,using a syringe and tube to suck from bottom of expansion tank repeatedly until only clear liquid showed in the syringe.

Refilled with everything free antifreeze and distilled water and so far no sign at all of a leak.

However I have bought a scrap pump off a low mileage bike just in case.

40 quid seems to be the going rate.

The nc seems to cope with low water unlike some engines that warp a head at the first opportunity.

 

[wjvh 999]

I have noticed a small coolant leak or seep in the area around the water pump on my 40k miles 2012 NC700S however the workshop manual states :  

MECHANICAL SEAL INSPECTION
Check the bleed hole [1] of the water pump for signs of coolant leakage.
• A small amount of coolant weeping from the bleed hole is normal.
• Make sure that there are no continuous coolant leakage from the bleed hole while operating the engine.

 

So, I find this quite reassuring in respect of my very low-rate seep.