Latest Update.
Took the car to a local automotive works (Peerless Automotive & Electrical) and within 30 minutes they diagnosed a blockage in the radiator core and/or engine. Most likely due to an additive that has been used in the coolant. I do recall about one year ago, adding the Redline Water Wetter additive and have not given it a second thought since. They noticed some black globules flowing within the coolant and also saw evidence of the radiator "sweating" near the top tank opening.
They indicated that at highway speeds, there is enough pressure from teh water pump to push all the globules through the core and maintain the constant temp (at around 91 to 94), but after entering the start/stop 60Kph areas, some of the engine idle water pressures may be insufficient to maintain the flow. This explanation is reasonably consistent with what I am seeing, although they qualify themselves by saying they could not rule out head gasket problems, but would need to do this anyway as a first step.
So they advised:
1. remove the radiator and send it off to a specialist for assessment (flush, repair or replace).
2. replace Thermostat, hoses and flush engine (while the radiator is being assessed).
Should be at least two days off the road.
I think I will request they:
a. replace the radiator, (with a largest one that will fit)
b. also add a solid aluminium overflow tank to replace the standard plastic one,
c. new higher pressure rated hoses/clamps to run at 1.3 bar instead of the standard 1.0 bar (nice blue silicone),
d. new radiator cap (1.3 bar), and
e. new thermostat (with a "fail open" mode).
Any comments on my shopping list? Sort of like a little "necessary" mod.
At least that is how I explain it to the missus.
Paranoia?
