redlimo

Would appreciate some advice on whether anyone has a likely explanation and possible simple fix before I take to the garage.

The coolant temperature indicator on my RB320 can vary from it's regular position just below the middle through to close to the top of the range. When this behaviour starts the indicated temperature rises up and down seemingly with no pattern. It happens most often during a long journey after about 30-40 miles. I suspect the problem is with the sensor and not because the engine is genuinely getting hot because the temperature can change from close to maximum back to normal and back again in a few seconds.

When the temperature indicator rises above the middle position the turbo fails to kick in which I assume is by design.

Any clues please? Apologies in advance if this is something others have raised already in the forum.

IggyRB320

iTrader: (9)

I hate to say it, but it may be HG failure.
You could try a 'sniff test' but this may not pick the failed HG up, as it probably only under boost that it fails.

What's the coolant level like & are there any oily spots in the expansion tank?

I hope it's something more simple & less expensive though, like a thermostat!

speedking

Start with thermostat.

d4vidh

Then the coolant temperature sensor

redlimo

Thanks all for the advice. After reading the response concerning HG failure possibility I did some more reading and unfortunately all sounds consistent. So no messing about - it's currently in the garage and unfortunately their suspicion too is HG failure.

If this turns out to be the case anyone got any ideas how much to expect it to cost from a Subaru garage? Anything particular to specify when replacing the HG? Anything to recommend to do also whilst the engine is out and the head is off?

DT-SPD

iTrader: (7)

Cost entirely depends on how much you want to spend but a good engine build is going to be £3k

As the heads have to come off I would fit new forged pistons, bearings and head studs. No point doing the HG only to have pistons fail once its all back together.

IggyRB320

iTrader: (9)

Shame that. I was hoping I was wrong..!

I guess it depends if your RB is still under warranty & if you want to retain it..?

But to be honest, I don't see any point in having a main dealer repair & fix with OE parts that will inevitably/potentially fail again!

The only way to go, is having a full forged re-build, that would be cheaper than a main dealer would charge for standard OE parts anyhow.

I'd definitely speak to one of the reputable tuners, Chevron Motorsport, Finch Motorsport, EngineTuner etc.
I'm guessing you could have the engine work done, with forged Pistons, race bearings & maybe pinned liners, with an uprated gasket & head bolts, for maybe £3.5K - £4K.
With an ECUTEK re-map, you could easily see a decent power/torque increase without any further supporting mods.
But your engine will now be solid & also support further modifications like uprated turbo & cooling, for much more power if you want!