I have my engine plumbed in as below

Thermostat to top of rad
small thermostat hose to top of rad
oil cooler to top of rad
water pump to bottom of rad
expansion tank outlet to T piece that goes to the small pipe on water pump and from unit on throttle bodies.
expansion tank return to small hose on top of rad.

My question is with the small hose on the top of the rad connected to the top of the expansion tank am I just pumping hot water back to the expansion tank which in turn goes straight into the water pump to be cycled through the engine?
Wouldn't it be better to block off the small pipe on the rad to force all water to go through the rad and out of the bottom hose back to the water pump? If so where do I plumb the top of the expansion tank to?

Hey Stu,
thats how i've got mine.
my understanding is that it's just for expansion, it's not in the main flow

heres a wee diagram of what ive got, works perfectly and has been seen by yamaha

You need your expansion tank to be plumbed across the flow to make it work properly.
Yours is in the same side of the engine flow.
Here is a copy of what I wrote on another thread:

If you haven't got an expansion bottle/tank, then fit one. It should be the highest point in your system.
The bottle should have two pipes. Probably a 16mm OD at the bottom and an 8mm OD at the top.
You should tee off your bottom rad hose (the one that returns to the pump) and plumb that into the 16mm pipe.
For the 8mm, tap off somewhere in the top hose to the rad or the top of the rad. You can also tee the 8mm into a cylinder head waterway or before the thermostat.
The different sizes and pressure difference ensure that there is a constant flow into the bottle via the 8mm and back out via the 16mm hose.
Not only does this allow for the water to expand when hot, any air will collect in the airspace above the water level, especially when filling from cold when the stat will be closed.
A closed stat is the most common cause of an airlock.
That is why you often see mechanics running the engines with the cap off (on none expansion systems) and topping up, but this can be dangerous, not just from getting burned, but the cold water hitting your hot cylinder head and cracking it.

sorry, was too big...heres the small version

A1, that is what I was trying to explain
Mine is plumbed like that and works perfectly!

Ahhh that makes more sense.
Just to clarify the connections at the expansion tank. The diagram shows 3 connections, my tank has two main outlets and a small one in the neck next to the cap (overflow).
Is it just the way the diagram has been drawn and the two breather connections go to the top outlet on the tank or does one of them go to the overflow?

Sorry if it seems I'm being dim

[Edited on 16/4/09 by stuart_g]

You need to tee both of those pipes into the single small inlet and the overflow from the cap it just needs to vent via a pipe under the car

[Edited on 16/4/2009 by nitram38]

That's what I thought. Thanks for clarification

cheers for this thread chaps, just realised we have a pipe missing on our two installs, we have a single pipe from the throttle bodies to the pump, no T to the top hose / expansion tank. Can't believe I missed that in the hand book, I assume its important so will rectify next week.
At the moment I have the thermostat bypass hose T'd into the top hose just prior to the rad, I then have a T from the bypass hose at the rad end into the expansion tank top inlet, does it matter where I T the hose from the pump / throttle bodies in?, can I T this in just before the inlet to the exp tank?