Not quite done yet Jeff. To keep this on record I thought I would add this info gathered today. Bit of a gobfull so bear with me.
28-07-11
Replaced Jeff’s stat and re-bled.
Sometime in March of this year, Jeffs Bongo was suffering from overheating symptoms. The system was inspected and faulty components replaced, the stat being one.
A new Mazda stat was originally installed to replace the one on the right which had had its jiggle pin removed and flange drilled.
This is the Mazda stat taken out after 4 months service (Note the chalky deposit on the underside - this deposit is quite thick)
– a genuine Mazda, which had been subjected to the following:
This stat was installed in March 2011 and replaced today after the following history.
Having replaced the original stat and found the overheating problem was still there, it was decided to try the Steel-Seal route.
The first attempt lasted for approximately 1000 miles before the system erupted again.
A second attempt at the Steel-Seal solution was made, but this only lasted some 400 miles.
The head was removed and found to be cracked.
We replaced the head and forgot all about replacing the stat.
A TM-2 was fitted with the sensor located at the metal pipe from the head (top hose).
Data was gathered and the system appeared to be running within the range 86 to 92°C, a span of 6°C.
Comparing these figures with my own (82 to 86°C) was when I realised that Jeff’s stat had not been replaced when the head was done, and a probable cause of Jeff’s higher temperatures could be that his stat had actually suffered a temperature which had caused the expansion tank cap to blow at the pressure of 1.1bar.
According to Grahame, the temperature at which the expansion tank cap will blow is 120°C.
At this temperature, the thermostat has exceeded its absolute full travel and will have lost some of its wax, resulting in a ‘lazy’ stat. ie subsequent temperature cycles will cause the stat to lift, BUT later than it should (at higher temperatures).
So before we change the stat today, we put both of them into a pan of water (side by side) and applied heat.
By the time the old stat started to move, the new one had travelled approximately 2mm which equates to a temperature of 88°C.
Therefore, this particular overheated stat was beginning to open at 88°C, ie 3°C late.
The new stat was fitted, the system THOROUGHLY FLUSHED, the Bongo bled, and taken for a test run.
The TM-2 now records a temperature of 85 - 89°C, a span of 4 °C (50% better than the other one.)
Any comments/ideas on chalky deposit?
