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

[Stubby79]

I think mine took a while to warm up, iirc. And I wasn't driving it for economy...probably wouldn't get up to temp in cool weather until being on the highway for a bit, if I was.

Really cold days, it wouldn't put out much heat until I was climbing the hill just before getting off the highway!

The insight isn't much better.

[MetroMPG]

Thanks for the corroboration!

My parents' 2006 4-cyl Camry, on the other hand, generates usable cabin heat within 1.5 km of gentle driving from a cold soak start in freezing conditions. It's the warmest-blooded car I've driven.

Did you think of a title for your Insight thread yet? Can we split it off? Or maybe you did already and I missed it?

[Stubby79]

I did...was thinking of starting a thread. If I do that, is it easy for you to move the posts over, or better to move them to an unstarted thread?

[MetroMPG]

Probably best to move the existing posts first, since vBulletin preserves the date order -- the earliest datestamp in the copied posts will be post #1 of the new thread.


You can edit post #1 if needed, though.

[Stubby79]

I'll PM ya.

[wdb]

Originally Posted by MetroMPG

My parents' 2006 4-cyl Camry, on the other hand, generates usable cabin heat within 1.5 km of gentle driving from a cold soak start. It's the warmest-blooded car I've driven.

I think that's more a function of cooling system design/integration with HVAC. I have a BMW that puts out warm air within 2 minutes of being started. Engine temp takes forever to come up to normal, but the cabin is toasty. Our old Lexus on the other hand took forever to produce warm air in the vents, and yet engine temp came up fairly quickly. I think BMW does some trick with valves and water circulation to bring heat into the cabin as soon as possible.

[MetroMPG]

I wondered if that was the case.

Even a relatively smaller volume water jacket in the engine would achieve the same thing with a closed thermostat.

Of course, some modern cars are taking this to the next level: eg. coolant loops/heat exchange with the exhaust system (eg. hybrids) for reasons of efficiency & emissions.

Even the lowly Mitsu Mirage has a big resistor element in the heater box to both raise engine load after a cold start (speeding engine/coolant warm-up) and generate warm air for the cabin sooner.

But the folks' 2006 Camry really is remarkable: I drove it last night to pick up groceries for them, and even from a sub-freezing (-3C / 27f) start, it was already blowing lukewarm air within 1 km! 0.6 miles. And that's when being driven very gently.

The Miata is by far the slowest to warm up of any car I've owned. (I'm glad for the corroboration from Stubby... I'm not just crazy.)

It's definitely getting an inline coolant heater next summer.

[Stubby79]

I think you'll find it's a lot to do with the coolant's path...if some of the coolant(what goes through the heater core) can bypass the block, it means some of the coolant going in to the head is already warm, so it can heat up even further on the next pass...don't quote me, I'm just thinking out loud.

The miata flows it all through the block before going through the head...it all has to warm up to get hot.

Besides that out-to-lunch theory, the more likely culprits, in my mind, are the piston oil-squirters on the Miata, robbing heat that would otherwise transfer in to the cylinder walls/block/coolant, the design/materials used in the heater core itself, and the coolant itself...ie your 30 year old heater core is going to have deposits on it that the 15 year old toyota - and it's long-life coolant - aren't necessarily going to have.

Anyway, there are plenty of variables that affect it. It could all boil down to what they designed the cooling systems for...a summer sports car vs a comfortable daily driver. One designed to warm the passengers up ASAP, the other designed to shed excess heat as quickly as possible.

(oh, and the cast-iron block vs aluminum will probably slow down heat transfer from the cylinders, as well as the toyota's cylidners are completely surrounded with coolant/floating, vs passages around them in the iron miata block)

[COcyclist]

Originally Posted by MetroMPG

I still want more, though. I'm thinking next year's first mod will be installing a 1000w coolant heater. The car is very cold-blooded and it sure runs rich when cold. (I know I should also check the thermostat, but I don't think it's faulty - the car always reaches a consistent, stable operating temp; it just seems to get there really, really slowly. Even with a ~90% grille block. )

I highly recommend adding a coolant heater and perhaps a stick on Katz heater on the oil pan as I have done to my TDI. Also, coolant and thermostats are wear items. The thermostat will fail open but may do it slowly over time so that you don’t really notice. If you are going to open the hoses to add a tank heater, do a good coolant flush and change the thermostat while you are in there.

The tank heater will get some heat into the head but the oil pan heater will put heat into the whole engine compartment in 20 minutes. Put something on the windshield that is very visible when you plug in so you don’t forget as you back out of the garage. Don’t ask me how I know.

It takes me 30 minutes of driving or longer to start getting good mpg numbers.

[Xist]

Hey, it has been years since I have seen any discussion on defroster deletes or whatever the cool kids call it nowadays. I just ran across this: