Newer engine, 180* stat, LOWER fuel economy?!?

[Justin]

Stuffed a newer 2.8 in my Cutlass, from my first Cutty, RIP. Apparently I had stuck a 180* t-stat in it when I was in college for some reason, but other than that she's stock. Before the swap I could average 30 on the DIC fairly easy, even against the wind. Now I can't crack 26, no matter what. The only things I can think of are that either the 2.8 likes to run at 200-210, which is where my other engine ran, or that the injectors are really messed up from sitting for 5 years. Anyone else running a 180 stat and notice a severe drop in MPG? I'm trying to decide where to go from here, it's a strong engine, even for it's 140,000 miles, but just isn't the most efficient.

[Crazy K]

the tstat is easy to change. put a regualr 195 in and see what results. I have always thought incorrect tstats are a bad idea.

[ismellrealbad]

i could see a slight drop in mpg from running cooler. but only slight its only a 15* or so drop in temp so i dont know about 4mpg its prolly something else

 

i think 180 is perfect. 160 is too cold imo i also think its a bad idea

[Pontiac6KSTEAWD]

Unless you chip is programmed for the 180 Tstat, your fuel milage will suffer. The TCC doesnt kick in till 185?, So you are never really into the Cruiser zone. Also, a cooler engine is less efeciant than a warmer engine, however, a cooler engine also provides more power.

[mfewtrail]

I run a 180* t-stat in my '93 and it averages right at 30mpg on the hwy(sometimes a little more than that on flat stretches..). I'm going by actual calculated mileage, the DIC in my car reads a few mpg lower than actual.

 

Brian, lockup will occur ~130*F. I think Justin has getrag in his Cutlass anyway(?).

[Pontiac6KSTEAWD]

I guess it might differ from car to car. My 6000 doesnt occur till about 170 or so. I am running a standard 195 tstat in it. My tgp wont occur till I hit 130. but the temp guage never gets above 140, and I am running a 180 tstat in it. But thats besides the point, I see in his sig he is running a 5 speed. So the only other thing I can think of is a diferent size of tire, larger tires are more rolling resistence, and could lower fuel milage, a dragging bearing or brake, and the tranny could be geared difernt from his old car.

[CSI_MuNkY]

I have a 180 in mine and when I put it in my gas milage increased, I can't remember by how much, but between that and running royal purple religiously I have gone from 300km per tank up to around 450km per tank. I haven't done anything else to the engine aside from the odd tank with injector cleaner in it.

 

Jamie

[Justin]

See, the only thing I've changed is the engine. The trans is the same, wheel and tires the same, brakes the same, etc. Engines should be identical, the auto and manual 2.8 in '89 were the same, correct?

[kuwaitliberation]

What kind of weight difference between the old car an the new one (in this old and new refer to the vehicle the engine was in)? What does the drag coefficient look like from the old to the new? What kind of tires? Did you seafoam the engine (sludge build-up)?

 

There are a ton of things that can contribute to this if the engine sat for 5 years.

[94CutlassSLCoupe]

it may not be hitting closed loop, i'm not entirely sure what the closed loop temp is on these cars but if its still in open loop the cold start enrichment may still be running, and all these old gm cars seem to run pretty rich when in open loop.

[Justin]

it may not be hitting closed loop, i'm not entirely sure what the closed loop temp is on these cars but if its still in open loop the cold start enrichment may still be running, and all these old gm cars seem to run pretty rich when in open loop.

 

I was wondering that too, but 180 should be closed loop, that's awful close to normal operating temp. I'll have to check it out, that's for sure.

 

What kind of weight difference between the old car an the new one (in this old and new refer to the vehicle the engine was in)? What does the drag coefficient look like from the old to the new? What kind of tires? Did you seafoam the engine (sludge build-up)?

 

There are a ton of things that can contribute to this if the engine sat for 5 years.

 

See, I swapped engines, not cars. So the only variable is the engine, which is identical to the old one except for a lower temp T-stat and having sat for 5 years. I might swap the injectors from the other engine or do an injector flush, maybe they're really varnished up. Shouldn't be too much sludge, especially in the intake/heads as it's got a somewhat fresh head gasket job.

[toms92gpse]

I think closed loop starts around 150-160ish. I know when my tstat got stuck open my car wouldn't come but a hair above the 100 mark and stayed in open loop mode. It ran rich as hell, lacked some power and the gasmilage sucked, I went from24-25 to hight teens. 180 is warm enought for everything to operate normal even with a normal computer. If your computer hasn't been tuned for the cooler temp you will see a little bit of a dip in fuel economy but it will be like 1-2mpg at the most droping from 195-180.

[FordBoy]

I dont think a t-stat would cause that i think it is because it sat for 5yrs clean/replace the injectors or plugs/wires and see what happens

If a straight 6 jeep got better MPG then my cutlass would that be a t-stat issue?

 

[SigEpCutlass]

If the engine has been sitting for 5 years, there are a lot of other things I would look at first before I even considered the T-stat to be the source of a problem. Get your multimeter and test those injectors Justin! If they're in the proper range, then I'd look at plugs/wires/coils, and then maybe at the T-stat if everything else were ok.

[Crazy K]

what all got swapped along with the engine? what sensors and components piggybacked their way onto your car during the swap?

[Turbo231]

Could your DIC be off? What is your real MPG? By real I mean filling the tank, driving, refilling the tank and measuring your MPG.

[Justin]

If the engine has been sitting for 5 years, there are a lot of other things I would look at first before I even considered the T-stat to be the source of a problem. Get your multimeter and test those injectors Justin! If they're in the proper range, then I'd look at plugs/wires/coils, and then maybe at the T-stat if everything else were ok.

 

I think I'm going to do an injector flush tomorrow, see what happens there. The plugs and wires are pretty new, I believe I did them at the same time as the head job so they should have 10k on them tops.

 

what all got swapped along with the engine? what sensors and components piggybacked their way onto your car during the swap?

 

Most of the sensors were swapped with the engine, I can't really think of any that weren't.

 

Could your DIC be off? What is your real MPG? By real I mean filling the tank, driving, refilling the tank and measuring your MPG.

 

If the DIC is off now, it should have been off the same amount before. I've checked it before with the actual mileage and it's usually within a MPG.

 

It almost seems to idle high, but I don't think there are any vacuum leaks. I'll have to do a little checking tomorrow if I get time, hopefully our snap on scanner shows the rpm and desired rpm.

[mfewtrail]

I'm not sure about the actual temperature required for open loop, but I know closed loop can occur at a lot lower temperature than some of you posted. TCC lockup requires closed loop AND a coolant temperature of 130*F or so. I've seen a scan of a OBD-I GP that hit closed loop ~118*F fwiw.