dt125 rad cap seal / head gasket
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It’s not an overflow, it’s an expansion tank. The radiator cap lets fluid out as it heats and expand, then back in as it cools…
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If you are worried about a head gasket blowing, keep a check on the coolant level in the radiator. It will keep getting lower as coolant is blown out the expansion pipe. If it goes down an inch or so and stays at that level it’s just normal fluid expansion…
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@89dt125nick as others have said, it's an expansion tank, put it back on. Also bear in mind that the radiator pressure cap is set to open at a certain pressure, these can fail and open too early.
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hi guys, i will replace it then as i didnt realise the coolant went in and back out of it, i thought it was just there to catch expelled fluid, so there is the one main line into the bottom of the expansion tank and what seems to be a thin overflow at the top, there is no lid on my expansion tank, am i right in thinking this tank is not pressurised and i can just make a cap for it? many thanks.
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@89dt125nick it's only a rubber cap. Not screw on so I guess it wouldn't hurt to use a home made piece. You can buy it from yambits for £8.60.
https://yambits.co.uk/dt125r-coolant-recovery-header-tank-cap-p-84230.html -
@89dt125nick yep. Line in and an overflow that empties into the frame on mine…
Try and fix it to the frame on a tether so you don’t loose it if it pops off… -
ok guys, thanks for the info, so when i refit it and top my rad back up, should i leave the overflow empty or fill it up and what should its behaviour be so i can monitor it. Many thanks.
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There should be markers on the reservoir. About 2/3’s full, if I remember correctly…
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hi guys, i have refitted the resevoir and the associated lines and topped up the rad and filled up the overflow tank to the upper line, when engine is warm and revved its shooting coolant and bubbles out the overflow tank and it smells like exhaust fumes, it has been like this when i bought it earlier this year, i havent even ridden it apart from 2 minute ride when viewing. So im going to whip the head off and inspect, is there any advice on anything before i do that, perhaps i am missing something, doubt it but 2nd opinions are welcome? Looking to get it roadworthy before autumn, even with this issue the engine sound great, revs freely and ticks over nicely as my neighbours will contest to. Many thanks all.
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@89dt125nick Sounds like head gasket
30 minute job to put right though. JUST ONLY BUY GENUINE OR ATHENA HEAD GASKETS. Don't buy the cheap white head gasket, it'll just fail.
I know @SpookDog had nothing but problems doing his head gasket, he's since modified his head and it's been grand ever since. So might be worth checking out his thread if this is a reoccurring them.
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Drain the coolant properly before and when you take off the head take some pics. You want to see where it was leaking from the coolant jacket into the bore. Also look for the root cause, head gaskets don’t usually blow unless there are overheating issues, or (in my case) misfire problems…
Buy a price of plate glass10mm x 30cm x30cm to lap the head clean and smooth…
Don’t buy a shitty head gasket, get an Athena, Vertex or genuine head gasket…
