How much more gas do you use in open loop? (or closed, wichever it is that it's at when you start the car) because i get horribal gas milage and my dad brought it to my attention that i never drive more than a few miles at a time, my engin temp never gets higher than around 130 unless im going somewhere different, all i go to is school wich is like 3 or 4 miles away and work wich is like 5, but then when im there it cools off cause im there so long and when i go places my friends drive, is this why im getting horribal mpg? because im always in wichever loop it is?


on a side note im going to check my coolant temp guage today, what one do i need for my car, like 160* or 180* or 190*? i have a 89 iroc with the 5.7 liter 350

 

Fuel mileage would be worse on a cold motor - you're running richer until the engine warms up to temp.

You need to have at minimum a 180 degree stat - 160 is way too low - 195 is stock. Many folks run a 195 in winter, and a 185 in summer, so the car gets to op temp quicker in winter when it's cold, but doesn't get so hot in summer.

If you swapped to a cooler thermostat due to a cooling issue, then you need to go back and find out what's really causing that cooling issue. Most folks 'think' their car is too hot in summer because it reaches 220, 230, even 240. These cars are designed to run at those temps, and are supposed to run that hot. Unless you have a boiling over, you are not overheating. TPI car (like yours) doesn't even turn on the secondary fan until 238 - so even 240 is not too high of a temp.

But, you could also very well have another issue - what are you getting for mileage? Properly tuned 350 TPI should get 20mpg at least I'd think. I'm getting 17mpg on a carbed 350, FI should be better.

 

You don't say what your "horrible" gas mileage is. It may be normal for your driving conditions just not what you'd hope for.

 

Im getting like 10-12 mpg, dont know exact right now, but thats also straight city with lights no more than a mile apart but mostly closer, so that on top of the fact that its always cold would make sense that its that bad right?

And ya i was gonna put in a 185 if thats not what it is, my dad just suggested we check it just in case cause i got the car a couple months ago, but im pretty sure that all my milage problems are just cause im never warmed up right?

 

I use to get 18 MPG Average (stock 350 TPI SD setup, 700-R4 with 3.27 gears) and I would drive a lot of crappy roads with horse and buggies around. I would see over 20+ if it was highway/interstate.

Check to make sure the thermostat hasn't failed in open. I've had them fail before in my V6 beater cars and never get warm enough to use the heater... even after blocking air entry to over 50% of the radiator.

 

Well like I said fireturd I never drive far enough for it to warm up anyways, I'm probably gonna replace it with a new 185 one anyways sense I like in texas and winters arnt to bad and summers are HORRIBAL like 115* in august! Even if mine is fine its only like 20$ for a new one

 

Before I had my comp issues I was getting 24hwy with my 92z28 with 350tpi, 700r4, stock rear. Thats at 65-70mph too and I was around 180-220degrees.
Im hopin to get 10-12mpg with my built and carbed motor. Im runnin a 160degree thermostat in my new engine. Make sure u dont get a thermostat and a temp gauge mixed up. At oreilly I think mine was like 10 bucks

 

basically when your engine is cold you are in open loop. Meaning the engine isnt really be controlled by the computer so you are dumping fuel. A way to help get into closed loop faster is to installed a heated 3 wire oxygen sensor. never run less than a 180 stat.

 

If your only ever making short trips, yes your MPG will suck. Another thermostat isn't going to help. Maybe warm the car up for a few before driving - although that may worsen average mpg.... My 87 305 with no computer controls, no cold start functions, a carb that is leaking fuel externally, setup for a 77 GMC pickup, no lockup converter, and a header leak averaged 14 MPG driving to work and back (average 30 mph, multiple stop lights, 10 miles each way).

 

Geese I don't feel so bad, some of you get crappy mileage.

My Buick that weights more then 2 3rd gen, 6500lbs] gets 15 driving like I stole it with a modded Buick 350 n race built trans, still just 2:90s out back but I don't do eway, just around town rabbit stops n starts.

I want to go EFI to get more but maybe I should be happy


good article on t-stats which has me run a 180 now
http://www.carnut.com/ramblin/_cool3.html

 

A Hummer H2 weighs 6500 lbs what the hell Buick do you have? An Enclave doesn't even weigh that much.

 

GVW on the door is 5772, add just me and that makes it 6000, add my stereo system n 2 boxes, tools, hydro jack n junk I carry all the time, and easy 6500 rounded up.

15 flat 1000ft, 18.02 1/4
[once I get the EFI n turbo installed, that should cut it down more]

 

Open loop doesnt necessarily mean it runs richer..it just doesnt have a way to alter fueling if the air conditions change due to altitude/temperature/humidity/etc. The engine gets fuel based on the computers preset fueling functions which sometimes CAN be too rich but sometimes too lean depending on your mods and what you set them to.

I tuned my 383 to run straight open loop and targeted around 15.0 to 1 air fuel and it would get near 16mpg city/driving hard and probably 20-22 mpg highway and I didnt really try tuning for mileage. That wasnt that motors intent, it was a mid 11 second street warrior build. Point is, closed loop doesnt mean lean and gas mileage.

Colder motor at first, usually is richer. You usually have a cold start enrichment and it decays as motor warms up. You'd have to monitor air fuel to see if this is the case and look at your open loop vs engine temp tables to see if the computer is commanding a richer/leaner air fuel.

can also log it to view commanded and narrowband o2 voltage while its in open loop.

 

if the OP doesn't have to stuff setup to log or view data

a simple volt meter can be used to watch the O2 signal as you drive.

"the slope around 400mv, which is 14.7:1, or perfect combustion, is very steep. This is why only computerized fuel injection systems can really hold anything close to 400mv."



stolen off this page
http://www.bob2000.com/carb.htm

 

Thats a good curve as I have found the closer you get to around 900 mv, the closer you are to 12.8 to 1 air fuel for WOT. 400-500 mv is the cruise range.