Keep having to top up coolant

by Basil Moss Sat 24 Aug 2013, 7:45 pm

Just lately I've noticed I keep having to top up the coolant, maybe every 500 miles or so, can't work out why this is. For the first year I had the bike I don't think I ever topped it up. It never overheats, and is running fine, I've not been able to locate any leaks either. Assume it must be a really tiny leak somewhere.

What should I do? Worth trying some product like Radweld, or should I just ignore it and keep topping up?

by davetheworv Sat 24 Aug 2013, 8:44 pm

whatever you do, do not use radweld.it causes more problems than it fixes. trust me i know

by **badseeds** Sat 24 Aug 2013, 9:11 pm

Check the oil to see if there's coolant in it. If there is, suspect the head gasket.

by teabag Sun 25 Aug 2013, 8:48 am

yeah check for oil contamination ,if theres no leaks its probably the head gasket as Badseeds said,exactly the same happend to a mate of mine with his old vfr

by alanesq Sun 25 Aug 2013, 9:02 am

It could be a very small leak somewhere which is difficult to see?

You can get a dye to put in the coolant then go over the bike with a UV light to check for any leaks (not something I have done myself but sounds a very good idea before taking the engine apart).

search ebay for "Leak Detection Dye kit"

by Basil Moss Sun 25 Aug 2013, 9:59 am

OK, will look out for leak detection kit. The oil looks and smells just fine whenever I check it - no "mayonaise" on the dipstick. That said the quantities are very small so perhaps it wouldn't notice yet? Last oil change was a couple of months ago and it looked like normal used oil.

by **badseeds** Sun 25 Aug 2013, 10:28 am

If it's just a small amount of oil you're losing it could be the output-shaft oil seal; no. 36 on here.

Oddly, both my CB500s and my VFR800 are leaking here, not enough to warrant me being arsed to fix them in a hurry, but it's happening. Look for oil around the left-hand side pivot point on the main-stand.

by Guest Sun 25 Aug 2013, 5:35 pm

I had the head gasket fail on mine; no mayo in the oil but the coolant was being pressurised and spat out of the expansion bottle.
You could get a sniff test done on the coolant, that would give you a pretty good idea.
Don't use radweld as it will block the pipe that goes from the filler neck to the expansion bottle!

by Beresford Sun 25 Aug 2013, 5:46 pm

teamster1975 wrote:Don't use radweld as it will block the pipe that goes from the filler neck to the expansion bottle!

It will also permanently ruin your radiator and clog up the smaller water passages inside the engine.

by Specialistpea Sun 22 Sep 2013, 10:10 am

I'd second the not using rad weld( other products are available!). Having used in I am now having overheating issues.

Bit is generally Ok and then if stuck in traffic will periodically overheat really quickly. Went into the red.

Can anyone recommend a way of getting rad weld out of the cooling system, I have replaced the radiator and cleaned the thermostat.

Having cleaned the thermostat the central metal (gold?) bar looks slightly bent. Is it meant to be or is it knackered?

Any advise welcomed.

Also new fan needed if anyone has a spare they want to sell

by ryancook1993 Sun 22 Sep 2013, 10:28 am

Are the radiators a common problem on these bikes then? I had a 91 rg125 FUN and my dad had it before me, we had it for around 10 years and never had to replace the radiator and I rode it alot while I had it!

edit: I missed the point! I only had my cb a few months and I needed a new radiator. Started out as a small leak then got seriously bigger lol.

by Specialistpea Sun 22 Sep 2013, 10:37 am

No major issue with the radiators, more that the bike is 14 years old and gets used all through the year so radiator tend to get dirty and worn, it was still on the original as far as I'm aware. - Also the fans tend to get rusted onto the radiator.

Had previously plugged a hole with a small bit of fibreglass glue which worked well for a few years and I'd recommend instead of rad weld if you know where the hole is and can repair from the outside.

by ryancook1993 Sun 22 Sep 2013, 11:25 am

Hmm I suppose, but so was my rg used through winter and it was 21 years old and on the same radiator for a minimum of 10 years.

by Specialistpea Sun 22 Sep 2013, 5:56 pm

That confirms my point, mine was on 14 years, yours was on your RG 10 yrs, then replaced then on 11 yrs. Thus no issue with CB500 radiators. I'd consider anything over 10 years fair wear and tear if used all year around. It was stone damage that caused the initial damage to the rad rather than the rad itself crumbling.

by ryancook1993 Sun 22 Sep 2013, 11:36 pm

No, we had the bike and never changed thr radiator, thats why I said minimum 10 years. However I agree that 10 years is a fair old time for it to last. I just read someone on here say they sprung a leak after every winter, which is a LOT lol.

by Guest Mon 23 Sep 2013, 12:21 pm

Specialistpea wrote:Having cleaned the thermostat the central metal (gold?) bar looks slightly bent. Is it meant to be or is it knackered?

This happens when the coolant temp gets into the red and boils over; the thermostat opens too far and pops off the guide pin.
If the 'stat is in this conition you should be able to centralise it on the pin and it will close normally.

by Basil Moss Tue 24 Sep 2013, 10:50 am

I found the source of the leak - an O ring between the thermostat and radiator pressure cap housings. Got a new O ring from a local valve shop and fitted it - good as new!

by Guest Tue 24 Sep 2013, 11:13 am

Nice one Basil! Very Happy

by Specialistpea Sat 28 Sep 2013, 10:26 pm

thanks for the heads up, I did buy a replacement thermostat housing from fleabay before I read your response. So will probably swap it over anyway tomorrow and unbend the original and keep it as a spare!

Any tips on trying to get the dregs of radweld out of the system? was thinking of attaching the garden hose to the cooling system and giving it a squirt but was unsure if this would damage the water pump??

by ryancook1993 Sat 28 Sep 2013, 10:38 pm

I did that and it did not seem to have any adverse effects for my bike, however I would wait for other responses lol.

by teabag Sat 28 Sep 2013, 11:31 pm

flushing the system through with a hose will not damage the water pump,as you know the waterpump has a impeller which basically spins pushing the coolant through it,if you attatch the hose it will just spin the impeller ,no harm done.
You could if you can be bothered take the water pump off and give it a good clean then flush the system through again.I changed my coolant when i first got the bike and after draining the old coolant flushed it through with the hose.

by **eternally_troubled** Mon 30 Sep 2013, 12:44 pm

Yes, running the hose through it isn't a bad idea.

If you have the time and inclination it would also be a good idea (after using the hose) to fill the system up with plain water (from the hose, in fact), run the bike until it is hot (fan comes on) for a few minutes, switch it off, wait a while for things to cool a bit (probably an hour or two), then drain again - this should help in getting anything left out.

Obviously you then need to refill with antifreeze and water (I use the blue stuff from Halfords).

by Beresford Mon 30 Sep 2013, 3:14 pm

Anybody ever used central heating de-scaler for flushing . I'm told it works well.

by Basil Moss Mon 30 Sep 2013, 8:46 pm

I cleaned my cooling system last weekend - drained, ran water through it from the hose, then filled up with flushing stuff from the garage, ran till hot for about 15 mins, let cool, drained out all manner of horrible filth, rinsed again and refilled. Will be interesting to see if it runs any cooler, as there was some scale in it before - I suspect a former owner had used tap water...

by Ricky Sat 22 Apr 2023, 7:04 pm

Basil Moss wrote:OK, will look out for leak detection kit. The oil looks and smells just fine whenever I check it - no "mayonaise" on the dipstick. That said the quantities are very small so perhaps it wouldn't notice yet? Last oil change was a couple of months ago and it looked like normal used oil.

I saw that happen before ..there is an overflow tube/pipe under the engine..sometimes the bike spits out coolant fluid ...maybe it is as simple as that..

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