Getting 0.49v drop across IRFZ44N MOSFET on heatbed...

So I beefed up the v1.3 boards circuit with solder for both the molex to the source of the mosfet, from the drain to the new screw terminal and from the positive on the molex to the screw terminal. And I am still measuring almost half a volt drop across the source to drain on the mosfet. This means my heatbed struggles to get to 105 degrees. I have been told the IRLB8743 is a better option but I can't find any in Australia and the only ones I can find online come from Hong Kong (just recently things have been taking over a month to arrive from China).
So my question is will this MOSFET upgrade solve my voltage drop?
And what is a reasonable voltage drop across a MOSFET that is at 60 degrees (fan cooled with heat sink) and handling heatbed amps?

Edited 1 time(s). Last edit at 01/28/2013 05:11AM by Phizinza.

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I have been told the IRLB8743 is a better option but I can't find any in Australia

How about this one? [australia.rs-online.com]

There are more MOSFET options going almost as good, see [reprap.org] .

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Those are out of stock so I ordered these [australia.rs-online.com]

Hoping they will work, looks all the same as the other one but just higher amps..?

Gate threshold is pretty low, so you should be fine.

Cool, thanks Annirak.