Hello everyone, I recently aquired a beautiful '86 Sport and I just wanted to say that this forum has been a great resource. I've been trying to make sure the car is completely up to date maintenance-wise and a coolant flush was high on my list. I had the system flushed and the thermostat replaced. The green 50/50 Prestone stuff and a Mazda OEM s4 thermostat and gasket (ordered from Mazdatrix) were used. After searching here I know I should NEVER trust the stock temp gauge but here's what's happening:

Before the flush:

The temp gauge would read 1/4 way up when warmed up and stay about there when idling or driving under 3k. The needle would start to rise when driving over 4k, almost 1/2 way up on hot days. That's when I decided to change the coolant/thermostat.

After the flush:

The temp gauge reads almost 1/2 way up when warmed up and doesn't move (it's rock solid) whether the car is idling or I'm pushing it.


What's going on? Is it the new thermostat? Is the car really running hotter or is the gauge somehow off now? I haven't noticed any ill-effects such as lights, buzzers, smoke, spilling coolant etc. but it's got me worried. Any input would be appreciated.

 

is it pushing coolant into the overflow tank?

 

no, I don't think so..

 

ok, I just went home and checked the overflow tank. The car's been sitting since Friday and there's coolant in the tank at the "full" mark. I filled it up to there so if it was pushing coolant into the tank it would have, well, overflowed out of the overflow tank or at least raised the level a bit.

 

I would say the thermostat is working properly and is closed when cold so the engine warms up faster.

 

I would hope so, I just don't understand why it's reading higher than before.. but I did some more searching and it sounds like 1/2 way is okay as long as it doesn't go past that.

People that have aftermarket water gauges have confirmed that the difference in temperature between the 1/4 and 1/2 way marks is only around 10-15 degrees so maybe it is running a tad hotter (perhaps lack of wetterwater which I had before). I think I'm okay though.. please someone convince me otherwise if I'm not.

 

you have a new thermostat, the overflow isnt overflowing, its not leaking, it should be fine. if its getting too hot, it will overflow into the overflow tank, so pay attention to that for a while.

 

There was a recal fix for 86 cars cooling system for just this reason. My dad had an 86 for 6 years, that basicly just pushed coolant into the overflow tank and wouldn't such it back in. It seemed like a blown coolant seal without the white smoke or bubles in the coolant. It was also a hell of alot less intense than the project car I bought that had a blown coolant seal.
It was also intermitent. Normal for weeks, then pushes all the coolant out, then back.

Fix for this is the 87-88 radiator with overflow cap on top of the radiator and a block off plate where the original radiator cap was.

If you get a new aftermarket 88 radiator ($130) and have an actual mazda OEM thermostat. Your car will probably run at with the temp gauge at the 1/4 mark.

 

ok, will do



Interesting.. thankfully it's not pushing any coolant into the overflow tank (so far) and it was running at the 1/4 mark less than a week ago.. one minute it's running at 1/4 and then a few hours later after a coolant/thermostat change it's running at 1/2.. it's obviously something they did (or didn't do), just don't know what? But as long as it's okay to run at the 1/2 mark I guess I will.


Thanks for the replies guys