Please delete
 

Done!

Yes...there is no problem whatsoever.

In answer to your wghat coolant....ask at a decent motor factors for one suitable for an alloy engine and with an anti-corrosion additive.

DO NOT be sucked in by such things as Subaru special stuff, other additives adding to the price, or waterless systems.

And tap water is fine for diluting it.;)

Thanks!

Do you really think that this is normal?
I've never had this with the WRX or STi before.

If its normal, is there any reason why?

Could be a voltage drop from the alternator slowing.
Could be the gauge sender going faulty.
Could be a loose connection on the gauge sender, (mine did that, I used epoxy glue to hold it in place, the top of the sender was moving about).
Could be the gauge going faulty.

TBH, I still don't think you need to worry, but is the car storing any codes?

The gauge is so inaccurate, it's not worth worrying. I have a defi coolant temperature gauge as well as the stock gauge. The stock one hasn't even moved by the time the Defi reads over 60.

And the oil temperature lags the coolant temperature by a good five minutes in normal driving.

No codes stored so far.

Time to change the coolant and do it properly.

If there's a problem with the coolant, the longer you leave it, the more likely damage will ensue.

And if it does damage the headgaskets, it's expensive:(