wildly fluctulating water temps

rossburns · Postby **rossburns** » Mon Oct 05, 2015 9:24 pm

hi all.
engine running cold during cold weather, in very hi range now we have hit warmer temps, its a 1991 na 6, radiator seems fine

davekmoore · Postby **davekmoore** » Mon Oct 05, 2015 9:34 pm

I'm certainly no expert but consider:
Old coolant
Dodgy thermostat
Air bubbles

Roadrunner · Postby **Roadrunner** » Tue Oct 06, 2015 8:50 am

Is the gauge quickly jumping up and down? or just getting hot and staying hot?
If jumping up quick it's most likely an air bubble.
If it gets hot and stays hot, make sure your fans are activating, theres coolant in the system, could be a stuck thermostat.

Do some preventative maintenance now before the really hot weather hits.
Flush the coolant. Change the thermostat while your there (its a $20 part, just do it while the coolant is out for piece of mind)
Use a quality coolant (I used Nulon concentrate and mixed about 25/75% coolant to demineralised water)
Fill it up and make sure you get every single air bubble out.

Rolley · Postby **Rolley** » Tue Oct 06, 2015 9:25 am

How old is the radiator?
It may have sanded up and only effectively flowing through 1/3 of its self.
When I pulled the tanks of mine when it failed quite a lot of the tubes were completely blocked.
unfortunately it's one of the things I haven't gotten photos of in my garage thread...

manga_blue · Postby **manga_blue** » Tue Oct 06, 2015 12:37 pm

davekmoore wrote:I'm certainly no expert but consider:
Old coolant
Dodgy thermostat
Air bubbles

x2 and I'd also add a faulty temp sensor unit for the temp gauge. The gauge and the ECU use different sensors. If you've got some means of monitoring the ECU one against the gauge one it might be interesting. If you haven't then another way is to switch off a warm engine then turn the igntion back on and see if the gauge reading goes down normally. I've seen one that went halfway down then suddenly shot up to boiling.

Possible, but less likely, is the temp gauge itself. Nippon Denso made a whole lot of temp gauges in the 90s and 00s with a dry solder joint. They'd go randomly all over the place. I know it affected SUV Mitsus and Toyotas, not sure about Mazdas though.