Renamed, Head Gasket Leak, Solved

  • Hi Lads

    got a strange coolant leak.

    no visible coolant leak externally from rad, pipes, or engine, have removed carb warmer pipes to remove the carb from the equation,

    the system isn't being pressurized like it would if the head gasket had gone.... altho i haven't discounted that.

    NO contamination of Gearbox oil so i can assume the impeller seal is sound

    now am i right in thinking i could only be left down to 2 things.

    bad radiator cap.. anyone have a valid DIY test for one ?

    or the base gasket internally not that i've ever known one to leak?

    only losing about 50ml every journey

    cheers 🙂

  • Just out of interest what head gasket was used on the bike.

    If it's not leaking anywhere, and it's not in the gearbox then it can't be much else.

    It could only be one thing.

    It might be the head gasket but it's only just starting to go.

  • Genuine yam head gasket, head and barrel were both skimmed professionally, wasn't a DIY at home job.

    just took a closer look at my rad cap looks like the rubber seal around the to has cracked and perished, could do with a new rad anyways the fins ain't brilliant

  • This post is deleted!

  • @tomimsmith1992 You'll need to post the direct link for the photo to be viewable on the forum. I'd say it's more than likely going to be the radiator cap or as Calum pointed out the head gasket is on its way out!. You should start by changing the radiator cap firstly and see how it goes.

  • Cheers @Biker_123, was looking for an attach image option, (i presume that has been disabled limited server space possibly?)

  • That cap looks alright to me, I'm using a worse one than that on my right hand side rad.

    I had this problem as well last year, I would use alot of coolant but the Water level in the rad would pretty much stay normal, 4000 miles of this, I still have no idea. No leaks!

  • @tomimsmith1992 no problem mate! Yeah it's just the direct link as Calum runs this website of his home network. Having a little look though at this radiator cap it actually looks pretty clean I've seen worse! If you have a spare radiator cap to hand give it a try and see how it goes and if it's the same situation probably best to investigate the head gasket,the cooling system seems fairly simple on these bikes so shouldn't be hard to find the culprit .

  • ill try a different rad cap, if that's not the fix i'll swap out all gaskets and jubilee clips, iv purchased a second hand rad anyways, had new samco hoses a few months back so effectively should have a new system lol 🙂

  • @tomimsmith1992 Great stuff mate 😃. Keep us posted on how you get on but I reckon you've got this covered with those parts you have..

  • cheers @Biker_123, still surprises me how simple these bike in theory are, yet throw up some odd things i suppose that's what you get when your bikes 16 years old lol

  • @tomimsmith1992 definetaly mate lol it's of a simple design the bike but can still leave you scratching your head! I know mines does anyway ... 😂

  • just a update, replaced with known good rad and rad cap, and replaced all jubilee clips,

    done a oil change while i was at it, can confirm no water in oil so water pump seal is sound,

    so iv ordered a full yammy gasket set from Jacksons, my local yammy dealer so will be OEM gaskets.

    i think you are right @Calum its going to be a internal gasket leak,

    have remembered i never did re torque the head, unfortunately is probably to late to rectify that now 1000 miles to late lol

    so in a nutshell,

    rad OK
    rad cap OK
    waterpump seal OK
    coolant pipes OK

    all that remains is the gaskets in the top end so as a process of elimination that must be where the issue is


  • FYI Athena gaskets are perfectly good. Athena make gaskets for my Turbo motor and they are reusable sweet quality gaskets and I will be using them on my Rotax build.

    I did the same a few years back on the belgarda build. Used oem but for the price it's kinda not worth it.

    Unlikely, but it could be leaking around the thermostat when under load, and because the cylinder head is hot it just evaporates.

    I only say head gasket because if it's not leaking and it's not the gearbox then I can't think where else.

    If it was the head gasket it will pressurise the overflow

  • i agree have always used Athena gaskets just have a bigger budget than usual, best spent on gaskets or i'll only go and spend it on something useless otherwise ahah 🙂

    i have always run my bike without a thermostat, the temp needle has sat nicely about a quarter of the way into the "running zone" no matter how much its being thrashed. full gasket set so that will be replaced as well anyways,

    iv had a few head gasket failures on some of the off road bikes and the DT all usually pressurize the system eventually overwhelming and opening the rad cap and dump the coolant into the expansion tank till it overflows, can usually tell with the bulging pipes above the thermostat. and the water puddle on the floor and the exhaust fumes in the rad.

    this issue unfortunately doesn't show any of the tell tale signs. possible pinhole size leak in the head maybe.

    im not a fan of products such as rad weld and wonder weld etc.,... but might run a bottle through it just in case there is a pinhole leak in say the coolant pipe which runs across the front of the engine or behind a exhaust stud??

    is re torquing the head a must. logic tells me once torqued correctly at cold the clamping force should only increase with the metal expanding when hot ? so surely there would be no way of it become slack ?

    anyways as always thanks for the advice 🙂

  • Tommy, if I can give you one advice you can take away it will be this.

    Always, always, always run a thermostat! It is imperative that you run a thermostat.

    The reason for this is because a thermostat creates a restriction in the cooling system. This raises the pressure inside the cooling system. A cylinder head requires around 40-60 psi of pressure in the cylinder head. Failure to do so will cause stale pockets to form of hot gases in the head. This becomes increasingly hot and will warp the cylinder head and cause the head gasket to blow.

    Rad weld should only be used in an emergency to get you home. It should never be used on a system you care about. It's bad for aluminium, which your engine is. It clogs up the radiator reducing the efficiency.

    To be honest we may found your problem mate! Put the thermostat back in. This restriction, combined with the blown head gasket will cause the expansion bottle to overflow. Indicating that the gaskets gone mate!

    Please read and take that on board. It's sound advice.

  • And the problem has been found @Calum & @Biker_123 you were right! tiny head gasket leak !

    so what do you guys reckon go for another skim this heads already had 3 passes and the barrel 2 so that will be 5 thou taken of i would have thought?

    also is it one of the guys on here selling the copper head gaskets on ebay? i know older engines used to have copper gaskets... are the rated highly for the use on DT's ?

    as always advice aprecated

  • @tomimsmith1992
    I have no experience with copper head gaskets but they are used in high performance engines when composite gaskets don't cut the mustard.

    That cylinder head has seen better days!

    As said always run a thermostat

  • Thermostat has been ordered from yambits, i had no idea it could cause such adverse effects ....

    I'm going to go the copper head gasket route give it ago... Whats the worst that could happen 😏

    Yeah the heads a bit battered ill stick a post in the wanted section for a replacement.

    Will I be ok to re skim the head do you think how far from detonation am I thats the question....

  • You will have to measure the squish band to really be sure. If it's that bad then you will need to double up on the base gasket to bring the compression ratio back down.

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