weep hole and water pump seal

Coolant water dripping from the hot engine


You know the smell of a hot engine after a nice long ride - if that smell changes from oily metal to burnt sweet it is time to check out the area around the water pump.
Seeing water drops coming out of the hot engine and then being vaporized is a bit unsettling at first since I had no idea there was a hole in the engine with just the job to leak water or oil.

meet the weep hole, your indicator that a seal is leaking

In this post you will learn a bit about what keeps your engine cool, where the weak points of the system are and maybe how to fix the problem.

Let´s start with the diagram of the water flow from the Malaguti Spidermax and her Piaggio MASTER engine with 500cc.
The same engine what moves the:

- Aprilia Atlantic 400/500
- Aprilia Scarabeo 400/500
- Gilera Nexus 400/500
- Gilera Fuoco 400/500
- Piaggio Beverly 400/500
- Piaggio MP3 400/500
- Piaggio X9 400/500
- Peugeot Satelis 400/500

Most scooters have one heat exchanger (radiator), the Spidermax has two what are regulated with an extra thermostat. 

9,8,7 cold - 9,8,7,1,5,6 warm - 9,8,7,1,5,3,6 hot
water pump and secondary radiator

primary radiator with cooling fan and expansion bottle
the 3 air bleeding points - 1 engine - 2 primary radiator - 3 secondary radiator

After understanding a bit about the ways of the water, we take a closer look at the water pump.
As usual during the development of an engine, there are some differences.

In the Euro 3 version the one with the controlled catalytic converter the water pump was redesigned for easy replacement of the seals without removing the flywheel cover (special tools needed).

BUT if you like me have an Euro 2 version then there is some more work involved.

Why does a water pump leak anyhow?
Well, there is the spinning part of the pump what is surrounded with water and there is the engine where it is mounted in and that just likes oil inside.
The water pump seal is mostly 3 parts.
1- the rubber oil seal what sits between engine and the water pump shaft.
2- the fixed ceramic water seal what comes next
3- the spinning ceramic water seal what hugs the pump shaft

The next 5 images are from a smaller engine´s water pump and it gives you an idea how it might look like in your water pump.

the oil seal
How does the water / oil leaks out of the engine?

you are looking on top of the water pump case, at the end you see the brown oil seal and in front of it the opening of the weep hole (blue). In case the oil seal fails, oil drips out of the hole and if the water seal fails - water.With this little hole your oil is saved from being "watered down".
For all your shopping needs Piaggio has some complete kits they offer to get the job done.

Euro 2 with catalytic converter

Euro 3 with the controlled catalytic converter

some dealers even carry the parts single

for later:
to check if the water system is OK with no air pockets see the lower part of this post.

2nd version of my weep hole water catcher
to make sure the water drips into the hose, a small part of the tie-down strap is inserted into the weep hole and sticks into the clear tube.

3rd version of my weep hole water catcher this time to see what amount is lost over a longer period. Test started at 50150km
the first result after some hill climbing and a short high speed part
The container will hold up to 50ml

after 1000 km at 51170 it is time to check how much coolant the Spidermax has lost
Looks like something less than 0.01 liter. That amount is nothing for me to worry so far.
It seems that the oil seal is leaking a tiny amount of oil also judging from the thin oil film on top of the coolant.
I will leave the weep hole discharge collector mounted and will monitor that for the the next 4000 km to see if there is a change in the amount of discharge.
If it stays this way I will do nothing, since changing the seals is quite expensive, so far the first estimate was at 180 Euros.

after 2000 km at 52197

It looks like the bit of radiator sealant I put in the system 2000 km ago is doing its magic. I might put in a bit more than the 0.02 liter what fit into the radiator cup opening the last time.
From the 25 ml the part below the black tie down strap holds it looks like 10 ml (0.01 liter) have been lost in 2000 km. At this rate the coolant needs to be topped up after roughly 2 years or 25000 km.

after 3000 km at 53167


after 4000 km at 54227


Yesterday we made a tour around our island (200 km) what took around 8 hours, kind of we did when I noticed the weep hole for the first time.
Checking the fluid stand at 55265 the glass was full.
So it seems at full stress (lot of mountains and high speed) over a longer time there is a lot more leaking than during a normal ride for an hour or two.
I emptied the glass and will check if my theory is correct.

after 5000 km at 55265


It seemed that my leak did seal itself for now.  Since it is not possible to check the water level from the outside anymore (the overflow tank material changed from being more ore less transparent to opaque.)
I am at 64000 km and have installed a clear pvc line into the water overflow tank connected to a hand ball-pump. The pipe goes down to the min level and every (nearly) time I am at the gas station I open the front storage and give the ball pump a little squeeze. So far there is coolant being pumped up and I did not notice any water out of the weep hole any more.


9000 km later at 73.000 km my ball-pump check still shows green. So far no more water loss happened. To read more see:


  1. Hi, Iam looking for the dimensions of Piaggio Master 500cc along with CVT.. Pls can u help me get the dimensions.. just the basic info of length width and height would do..

  2. hi,iam looking for the 2008 nexus 500ie Euro 3 with the controlled catalytic converter repair kit,and i found at AJ Sutton that water pump shaft was different,so where can i find on the web?thanks

  3. Hi I am looking for the special tool? Where did you buy it?

    Thanks J

  4. no, water on one side , oil on the other


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  6. I hawe problem
    Wather on the oil

  7. Supplier of Single Spring Seals- Single-Spring Mechanical Seal, Spring Seals, High Pressure Spring Seals and Single-Spring Mechanical Seal offered by Shanghai Trisun Parts Manufacture Co., Ltd, China.

    Mechanical Seal


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