Should have specified when I posted picsAssuming that the fluid that goes into the expansion tank returns when the engine cools down then that is normal. Indicators of a blown head gasket would be coolant being forced out of the header tank over flow pipe and, with the pressure cap off, you may see bubbles in the header manifold. If you have access to a CO meter you may also get a reading with the probe held over the coolant (NOT in it!).
I've never checked rad temperature with an IR thermometer so can't say with any certainty if the data you have collected is normal or not. I assume that they were taken when the motor was at 'operating' temperature, the readings taken one immediately after the other and the fan not running?
Perhaps someone else who doesn't have any cooling issues could do a similar exercise and report back their finding?
Your pictures show the coolant entering the top of the rad at 66°C and exiting at 50°C. What I don't understand is how the temperature rises to 74°C at the bottom LH corner, is 38°C at the middle top and 51°C RH top.
Without the fan running I would have expected the temperatures across the top to be similar and show a reasonably consistent drop as you go down the rad. That is my theory which may be a load of 'olloks and I'm happy to be corrected.
My gut feel (dangerous, I know) is that the radiator is partially blocked and it is this which is causing the issue.
Have a look here to see how to check the coolant temperature indicator operation.
Thanks yes I bought it and will do the test in next days as soo as I have time
That is the purpose of the design. As coolant expands it needs to go somewhere and that's the job of the expansion tank.Regarding your nice explanation on vmax's cooling system, then if I don't have to refill coolant it means it wasn't pushed out But recovered so should be fine right ?
Yes mechanic said he found lot of rust in cooling circuit, that's why he feared about a head gasket failure. Feared a rust corrosion.That is the purpose of the design. As coolant expands it needs to go somewhere and that's the job of the expansion tank.
In the 'good old days' it was necessary to check coolant levels as the displaced fluid was dumped out of the overflow. Those who checked would then fill up with water from the tap and over time the corrosion inhibitors were diluted which allowed crud to build up and get stuck it the narrow rad cores...you can work out the rest!
Thanks great advise on AMNormally the cores are replaced.
Note that there are aftermarket alloy radiators available that supposed to have higher cooling capacity.
Someone on here bought one but found the mounting holes we misaligned and then something else got in the way to prevent fitting.
WARNING: Those offering advice here are doing so based on what you have posted and their experience BUT that doesn't mean they are correct!Where you bet I bet then
So is it a good thing take it to a radiator specialist who will cut, open, clean and solder back?
Thanks for advise, don't worry was just because you're giving so many suggestions so I take them on big consideration, but of course I know you're thousands miles away, never saw the bike and just basing upon what I report which may also be wrongWARNING: Those offering advice here are doing so based on what you have posted and their experience BUT that doesn't mean they are correct!
Use their suggestions to make a diagnosis yourself before spending any money. Work through the system methodically so you know what isn't causing the issue and what's left is the problem.
If you haven't done it already, remove the heat shield and as the motor heats up use your hand to feel around the rad core.
You should start to feel it get warm evenly across the core; any colder spots will indicate a partial or full blockage.
IMO you skin is a more sensitive tool at these relatively lower temperatures.
As coolant temperature increases conduction will heat up the blocked parts of the core which may well mask the problem.
Got it, we're unsure about rad internal status even after acid treatmentThe water used to refill may contain calcium carbonates that over time build up inside the radiator (hence why I use deionised water).
There are branded products that supposed to remove that, also vinegar (an acid) has also been suggested.
I tried both methods on a car radiator but not convinced either was particularly effective.