Over heating? Help??

[Fazzer1996]

Hi there I have a Derbi senda drd 125 and recently when I ride for more than 5 minutes my bike gets really hot comes up on the dash flashing as its gone over the tempture and really hot also I can see bubbles in the expansion tank , I have put coolant in my radiator filled to the top, I have water in the expansion tank does that need coolant too or would water be okay?
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S.farrow

[RhynoCZ]

It could be:
a) Very lean mixture (not likely),
b) Stuck thermostat (I bet my money on the thermostat),
c) Faulty coolant pump,
d) Blown head gasket.
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'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

[Fazzer1996]

[RhynoCZ]

Is the thermostat working? The cooling system would work with nearly any fluid that contains water, even urine, if you were in need. So if the coolant pump is working, then it must be the thermostat.

Even if there was air trapped in the cooling system, it would still work. Now, there are 2 cooling circuit, if the engine is cold, the thermostat is shut and you only use the close circuit, then when the engine gets hot, the thermostat opens and lets the coolant through the radiator. If it stays stuck shut, then it's like if there was no radiator and your engine will overheat.

EDIT: The thermostat would be under a lid, that say ''NEVER OPEN WHEN HOT'' or something like that.
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'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

[Fazzer1996]

[RhynoCZ]

It's a simple job. Just swapping one part for another. It's also a cheap part (it should be around £15 to £20).

EDIT: The thermostat would be under a lid/cap, that says ''NEVER OPEN WHEN HOT'' or something like that.

https://www.adrenalin-pedstop.co.uk/upload/images/329c6-777_copy.jpg
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'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

[Fazzer1996]

[RhynoCZ]

The Internet suggests this could be the thermostat housing:

https://i.ebayimg.com/00/s/MTIwMFgxNjAw/z/bvwAAOSwjVVVrOJS/$_35.JPG

https://www.ebay.co.uk/itm/2012-DERBI-125-4V-WC-TERRA-GPR-MULHACEN-SENDA-THERMOSTAT-HOUSING-COVER-AOK-/261974513934
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'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

[Fazzer1996]

[RhynoCZ]

No need to replace the housing, be careful not to damage the seal under the housing (if you do damage the seal, then change the seal). Very simple to take it off, just 2 bolts and the hoses. Or at least that's what I get from the picture.

I'm not very familiar with your motorcycle.

It looks like the only seal that's there is a rubber O ring. So make sure you don't rip it apart, if you do, then buy a new seal (generic).
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'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

[Fazzer1996]

[bladerunner]

if there is air in the water pump it wont be pumping water either ...check if its got a bleed point on it. the thermostat can generally be removed and the housing replaced ( quick way to check!!) and finally if its not air in the pump or stuck thermostat then its shot headgasket etc.....possibly caused by previous over heating. This assumes its a coolant system fault rather than fuel or ignition etc
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Current bikes...cbr929, KDX200's, Rd125lc mk2, RGV250's

[Fazzer1996]

[Nemo]

Does the fan come on? If not check the fuse
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Previously owned: Kawasaki KH125, Suzuki GP125, Suzuki GX 125, Honda CB125 TDC '83, Honda ntv 600, Kawasaki ER5, Kawasaki ZZR600, Aprilia RSV 1000 Mille
Now own: Ducati 848 evo

[Fazzer1996]