bad mileage.. is it bad thermostat?

Hi,

1990 pickup 2WD w/ carburetted 22r engine w/ 290 000 kms (180k miles)

Bought this in the fall, about 4 months ago. It is averaging 7kms/litre or 16.5 MPG. I have read that others experience this poor mileage in the cold of winter. Onec warmed up, temp reads right in the middle of the guage consistently.

Am I right then to assume that I should replace the thermostat with one that will only open when the coolant is hotter?

Also, I noticed that the location of thermostat on this truck is below the distributor and above the alternator. Is it easier to get at it by jacking the front of the truck, dropping the splash shield and working from below?

Cheers,

Jai

How long does it take to warm up?
If it's hold a nice temp in the middle of the gauge and warms up in a reasonable amount of time (say 10min) then the thermostat is most likely ok.

Bad fuel economy is most likely from poor carb tune, ignition time etc.

16.5 MPG isn't too bad for a 22R with 180K.
The temp gauge reading in the middle is normal.
A complete tune-up might improve your mileage.

The truck warms up enough to drive in 4-5 mins. Temp gauge reads in the middle in 5-8 mins. Temps here have been freezing to about 20 below Celsius. (68 F)

However, the cab never really gets more than barely warm. I know that could be a problem with a plugged heater core and not a bad thermostat.

As part of a tune up, I have replaced: air filter (kn high flow) plugs (iridium), wires, rotor, cap, pcv valve, oil+filter.

I was under the impression that with a higher temp thermostat,the coolant rises to a higher temperature before it opens. In a place with a long solid winter doesn't the fuel economy work out better if the engine gets to run hotter? I am perfectly happy to be set straight on this if you think I have this wrong.

Cheers,

Jai

An engine best at the temp it was designed to.
A higher temp thermostat will simply let it run hotter.

That said, if the carb is not getting warm enough you may have issues as it won,t atomize the fuel properly.

Often there are coolant lines running through the inlet, or it maybe feed directly from the cylinder head.
Some cars, and I'm sure your toyota will be one, have a wide diameter steel hose running from the exhaust manifold to the air cleaner, usually with a switch for summer and winter that opens and closes a valve.

Check yous still has this, as the hose often rusts out and falls off.

The Hot Air Intake system directs warm air from the exhaust manifold into the air cleaner when it's cold.

On the underside of the intake manifold is the Cold Mixture Heater which warms up the mixture.

Both help with cold weather driveablity.

You could try changing the t-stat, you can always change back.

Thanks for the help.


Some cars, and I'm sure your toyota will be one, have a wide diameter steel hose running from the exhaust manifold to the air cleaner, usually with a switch for summer and winter that opens and closes a valve.

Yep, rusted out, barely holding on, no use. Will make a new one with aluminum tape and a valve of some sort.

The Hot Air Intake system directs warm air from the exhaust manifold into the air cleaner when it's cold.

On the underside of the intake manifold is the Cold Mixture Heater which warms up the mixture.

I will take a close look at this and make sure its all operating properly.

BTW if you thought I was being a wimp saying it gets down to 68 here in the winter, I meant -4 F is our average lately. Maybe I'll get a bra for my truck in the winter...

Jai

I decided I was too busy to change to change the thermostat, and now that the weather is nice again, the truck is getting much better mileage. I would say close to 9 km/L or 21 MPG. i think in the fall I will change the thermostat to see if there is a difference.

Thanks for everyone's input.
Jai

That's good.
In retrospect, a carbed engine will get lower MPG in cold weather because the air is denser (more O2), which leans out the mixture, so you use more gas. That aluminum hose from the exhaust manifold to the air cleaner housing helps heat the incoming air.
An EFI engine can compensate for that, so there's not much of a change.

Next fall you may want to flush your cooling system and make sure the heater core isn't plugged. If you still haven't got enough heat a higher temp t-stat may help.