My Aprilia RS125 keeps over-heating.

Cav · L Plate Warrior Joined: 23 Nov 2004 Karma :

I have a Aprilia RS125 Tetsuya Harada and I'm having problems with it over-heating.

When going along in open air, it runs at around 70 degrees C which I believe is the correct temperature for an RS125. If I hit traffic, it seems to ok for a while. It'll stay around 80-90 for a few minutes. As soon as the temperature hits 90, it seems to rocket and before long I have coolant escaping from the cap and dripping onto the engine which causes a lot of steam.

I have checked that there are no airlocks in the coolant, and that the air vents are clear. Apart from this, the bike runs perfectly.

Is it expected to overheat like this? I know that it doesn't have a fan on the engine and the only way it cools down is from air in-take, but surely they're not designed to get so hot? It has reached the high 90s many times and today it went slightly above 100 before I was able to pull over and let it cool down. The weird thing is that all I need is 20 metres ahead of me to quickly accelerate down and it drops the temperature by 10 degrees or so. It's more of a problem when the traffic isn't moving and I'm stuck, not moving anywhere.

Can anyone help, or give me some advice?

Cheers Smile

Guest · Brolly Dolly Joined: 22 Apr 2004 Karma :

the forst bit sounds quite normal, temp goes up when stuck in traffic, but it shouldn't boil over.

Have you checked the thermostat is ok, sounds like it's stuck shut.

mr jamez · World Chat Champion Joined: 04 Aug 2003 Karma :

So the problem is when you are stuck in traffic, the bike will get a lot hotter when sat in traffic as there is no air passing through the radiator. As soon as you get moving it cools down quickly. I would check that the thermostat is opening properley, that you have enough coolant in the system, if there is too much antifreeze the pump will struggle to push water round the system. Have you looked at the radiator to make sure it is not clogged up with rubbish and road debris?

Dom · World Chat Champion Joined: 06 Sep 2004 Karma :

I guess it might be worth putting new coolant in and having a good look at the radiator to see it's not blocked up. Just as a point of reference my RS ran at 70ish in the summer but is now running a few degrees colder and peaks at 68. As it gets colder I'll probably improvise something to block up part of the rad so it doesn't run too cold, perhaps a previous owner has done that on yours?

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Hi

My RS tends to cool down in traffic most of the time. Takes ages to get any heat into it when idling. Only time it overheated was when I put too much antifreeze to water in it and the impeller could not pump the resulting liquid round.

All the best

Keith
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mr.z · World Chat Champion Joined: 04 Feb 2004 Karma :

A guess but your readiator cap could be past its service limit...

The cooling system is pressureised, because at higher pressure the boiling point is higher, so it can get hotter without boiling over... i'm not sure how you check them but a trip to the breakers to get another might be worth a go?

If its getting hot rapidly then the thermostat could be stuck/knackered?

Another that the radiator is blocked, not cooling afficiently enough, flushing it out with a garden hose, then rad flush a few times then a couple of lots of deionised water and then the propper mix should get rid of any nasties that have got caught in the radiator...

Either way, try and get it sorted asap, overheathing might not seem to do any damage but its bad news, and being a two stroke it will like you even less for it (read engine rebuild allot earlyer than normal + possible warpage of engine insides)
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Cav · L Plate Warrior Joined: 23 Nov 2004 Karma :

Thanks for the replies Smile

I should have mentioned in my original post that I have replaced the cap on the coolant tank as I thought it might have been losing pressure, but that doesn't seem to have cured it.

The thermostat sounds like the most plausible answer so far. I guess I could test it by removing it? and see if that reduces the temperature? Would the only downside to removing the thermostat be that it would take ages to warm-up?

I would drain the system but I can't find the drainage valve :/

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Hi

If the problem is the thermostat then the radiator will be cool, but the same will apply if the coolant mix is too strong or if the water pump is shot.

You can check the thermostat, basically by sticking it in hot water and checking the temperature that it opens at.

Not sure about removing it. Chances are that on the RS it will just never warm up. On some cars removing the stat can cause them to overheat.

The cooling system drain is on the front side of the engine and is labelled "Aqua". It is a small allen key bolt and looks like one of the ones holding the 2 halves of the crankcases together.

All the best

Keith
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Frost · World Chat Champion Joined: 26 May 2004 Karma :

I had the exact same problem with my bike a week or so ago.

Turned out there were two cooland tanks , and i'd only been topping the one up. I topped the other one up and it was still doing it. In the end i undid the radiator cap, bled the system and topped the fluid levels up directly in the radiator.

Not had a problem with it since!