4kq bad mileage

[Brett Dikeman]

At 6:28 PM -0500 1/30/02, Brady Moffatt wrote:
>Hi all,
>
>My 86 4kq is getting really crappy mileage, but it runs well. It'll do about
>430km (265miles) on 58litres (15.3US gallons), so about 17mpg.
>
>So far, I've plugged vacuum leaks, new intake and exhaust manifold gaskets,
>new injector seals, adjusted CO back to spec with a sniffer, cleaned ISV.
>The car runs well, so I can't really complain, but my Audi guru mechanic
>friend (and the list here) seem to think I should be getting 25-28mpg. I
>used to, til I fixed a wire in the starter to enable the cold start
>inj/thermo-time switch to work. Think they're on all the time?
>
>Another hint is that the temp gauge doesn't rise much over 70C, still in the
>cold range, and the heater doesn't blow that hot, but the rad fan will cycle
>eventually.
>
>What gives? Any ideas?
>
>I'm going to change the thermostat tomorrow, but would that make sucha
>difference?

Sure, not sure how much though.  A stuck thermostat will cause the
engine to run too cold...and incidentally, wear faster; all the
tolerances etc are designed for when the engine is operating at the
temperature the manufacturer picked(which is why running a colder
thermostat is often not a terribly bright idea!)  More wasted energy
inside the motor = worse gas mileage.

Aside from that, other things that could affect mileage:

-dirty/clogged injectors giving bad spray pattern/incomplete burn
-clogged air filter
-O2 sensor past 60k miles
-plugs
-wires
-rotor and/or distributor cap

BTW, clean the throttle too with throttle cleaner.  Prolly won't make
a difference, but it just keeps things workin' smoothly.

One last note...if you're in a really cold climate, you can restrict
airflow to the radiator(I would experiment starting with something
that restricts flow, like a piece of screen material from around the
house, that sort of thing) as most truckers do when the weather turns
cold.  The engine reaches(and keeps) operating temperature easier(in
the case of diesels, they're so efficient that they don't put out
-that- much heat.)  Just gotta make -sure- you don't block too much!
Many diesel trucks have adjustable slats in front of the radiator,
pretty neat idea...

Brett
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