"MPGiata" modding thread: aiming for 50 MPG with a 1990 Miata. Update: success, 55 MPG!

[MetroMPG]

Thanks!

It's hard to believe I've had the car for 6 full years now (just over 15k km / 9k miles driven).


I still really enjoy driving it. It's a pretty zen experience cruising along the river or through the countryside in an open car on a beautiful day. More so than motorcycling, in my experience.

I envy the owners of the latest Miata/MX5, though. They'd probably be getting 50+ mpg with 1/2 the effort. And at higher speeds.

[Ecky]

Originally Posted by MetroMPG

Thanks!

It's hard to believe I've had the car for 6 full years now (just over 15k km / 9k miles driven).


I still really enjoy driving it. It's a pretty zen experience cruising along the river or through the countryside in an open car on a beautiful day. More so than motorcycling, in my experience.

I envy the owners of the latest Miata/MX5, though. They'd probably be getting 50+ mpg with 1/2 the effort. And at higher speeds.

More like 40 in my case, but the driving conditions are different, and my tires are most certainly not eco.

Steady cruising at ~100kph looks to be 40-45mpg, top down, using no tricks.

[MetroMPG]

Level roads, I'd say mine is good for about 45 mpg cruising at 80 km/h = 50 mph.



Sounds you'd probably be close to 50 at that speed?


Getting 50+ in mine requires a lower average speed & operating the engine like it's a hybrid whenever I'm off the power. Not to mention all the ecomods.

[Ecky]

Originally Posted by MetroMPG

Level roads, I'd say mine is good for about 45 mpg cruising at 80 km/h = 50 mph.

Sounds you'd probably be close to 50 at that speed?

Getting 50+ in mine requires a lower average speed & operating the engine like it's a hybrid whenever I'm off the power. Not to mention all the ecomods.

With high performance summer tires, and no major ecomods yet, I'd say low 50's is achievable steady-state cruising at 80kph.

I probably ought to make a speed vs mpg chart, now that you mention it.

[MetroMPG]

Not very aerodynamic, but fun & useful!



Transplanting a young white pine from my friends' place to mine.

[Cd]

Great to see you are still posting on the forum !
Now you can tell people that you literally stuffed a TREE in your Miata.

[MetroMPG]

One of these things is not like the other!!



Old one stuck wide open! This is going to really improve warm-up times.

Parts store says the replacement is a 192 degree unit.

[MetroMPG]

Wow! Big improvement with the new t-stat. It warms up like a normal car now - the needle is off the peg within one km of a cold soak start, where before it took many, many kms. And that's with a 90% (manually adjustable) grille block.

I don't know if it's possible, but I'd bet the old t-stat failed gradually, because I remember that it WAS working when I got the car (I tested it in a pot on the stove). I would have noticed a change this dramatic. So I'm thinking I got used to progressively longer warm-up times, until I noticed recently that running the heater dropped the temp significantly (even on low fan speeds).

Coincidence that yesterday saw a record setting segment MPG (by about 2) on a well-travelled route? Probably, right?

Also new: The engine RPM behaves differently with the new t-stat. It's doing some rev-hang between gears that it didn't do before. So, probably past a coolant temp-sensitive programming threshold it wasn't reaching before.

[freebeard]

Makes me wonder about the XFi's thermostat now.

[Ecky]

In the KSight I had a similar issue. I couldn't imagine how a brand new thermostat had failed open. Turns out when I had added a sensor to the thermostat housing, I didn't realize it was too long and was holding the thermostat open. Made a huge difference.