Need Help - Oil and Engine Cooling

I own a 1985 Pontiac Fiero that started out life as a pathetic 2.5L I4 4-speed and has had it's engine and transmission completely replaced with a 1985 GM 5-speed tranny and a 1988 Chevy Beretta 2.8L V6 that has been fitted with new and better headers, camshaft, performance computer chip, and thermostat set to turn the radiator on at a lower temperature (175 degrees F versus standard 190).

I am getting ready to change my oil and have been reading about oil weights. I live in a cold mountain town and I do like to drive sporty in the summers. Up until this point I have been using 5W-30 conventional oil because I was an idiot and thought the "S" on "SAE" stood for "Synthetic" and it does not. As or the weight, it's what it says on the oil filler cap.

I was reading on how many people use thinner oils to not only produce more horsepower but reduce friction resulting in much better gas mileage. The only problem is in the warmer weather it can prove to not be thick enough for the heat. On the alternative, synthetic is supposed to be able to take heat much better.

So because I live in such a cold area (maximum mid-summer temperature is 80 degrees F) I wanted to try a 0W-20 Fully Synthetic oil by Mobil 1. I know I want the 0 Weight Winter because it can snow up to three feet at a time and get extremely cold from early October to early April. But should I loose the 10 weight in operating temperature? I know my after market thermostat will help and the fact that it doesn't get that warm, but is it enough considering once in a while I do like to floor it up to 130-150 MPH and rev to 6000 RPM?

Also, will there be any problems running fully synthetic in my older engine? I have seen a few reports by people with older cars that once in a while synthetic oil can cause leaks on older seal designs.

I got an Idea - Here's a pole with oil's on it. You guys vote for witch one my specific car should use for maximum horsepower, torque, fuel mileage, and engine protection.

- Thank you guys so much!

I live in upstate NY we see temps to -20, I have always used 5/30 Mobil one. 85-90 is common July and Aug.

I live in upstate NY we see temps to -20, I have always used 5/30 Mobil one. 85-90 is common July and Aug.

Yes like I said up until this point I have been running 5W-30 myself. But if the thinner weight 0W-20 oil will mean better flow/horsepower so, as long as I don't red-line the RPM's and overheat the engine constantly, then why shouldn't I use it?

Either way I am switching to 0W-30 at least because the 0 Winter weight will be extremely useful up here at my altitude of nearly 10,000 feet. The oil needs to be as thin as possible in the cold up here, we can see temperatures hit -40 F and the thinner Winter weight will help flow better on those particularly cold days and the engine will start much easier.

But what about the normal operating temperature weight? Will 20 be enough so I can take advantage of the horsepower and the fuel savings, or will it be too low and damage my one-of-a-kind Fiero's engine?

That engine is really not built for 0-20 year round, based on metallurgy and internal clearances.

That engine is really not built for 0-20 year round, based on metallurgy and internal clearances.

I have put in Fully Synthetic 5W-30 Extended Performance by Mobil 1 as of today, but now I have a new issue. When you change the oil in a Fiero (especially when switching from conventional to synthetic as I did) it is recommended to reset the idle so the engine can get used to the new oil (Plus I had put SeaFoam in the oil 50 miles ago to clean the old gunk out as well as the intake to clean the intake valves and in the gas tank with Premium fuel to clean the lines and injectors). So after a nice test drive to break in the oil I disconnected the battery so that the ECM lost it's memory (this is how you reset Fiero ECM's).

Now this is where it gets complicated. My Fiero has been running rich because there is a vacumn leak just past the throttle body. Several of the smaller plastic lines running from the large intake to other parts o the engine after the throttle body have snapped and despite this it has been running fine other than using a bit more fuel and backfiring flames from the exhaust after high revving due to the rich running and therefore unburnt fuel being deposited into the exhaust. So no real problems there, I've heard from several mechanics that backfires cause no issues until you hit extremely large backfires only found in dragsters and cars with much larger engines running rich (Normally 4L V8 or larger; or 350 BHP), because the backfire on such larger engines can be so powerful it destroys the exhaust manifold or damages and even some times destroys the engine.

However, because of this vacumn leak when I reset the ECM and then reconnected the battery, it did not run correctly anymore. It did start the first time and "learn" the new idle successfully but it says to shut off the engine and restart it after the "learning" is complete to see if the learning took. The engine sounds like it starts and the spark hits the fuel and you can hear the engine actually running so long as you are still turning the key, but as soon as you back off the starter motor the car dies as if the fuel was cut-off all together.

Remember, the "learning" process itself went fine. The car started and idled all the way up to operating temperature, turned the radiator on and back off as it was supposed to (took about 15 mins of idling to get up to the temperature of 175 F to activate radiator; this is an aftermarket thermostat) and then I killed the engine as I was supposed to, but it just wouldn't get going again. I can reset the ECM time and time again and get the same result (running only the first time until another ECM reset).

Before the intake lines snapped I could reset the ECM all I wanted and it would do fine. How can a freaking air line cause so much damage to my car??? It still sucks in air just not through the main intake anymore, instead for the broken lines it should just be air for themselves, I don't get it!

Is there a way to temporarily correct the problem? I was thinking along the lines of fuel tubing finishing the connections as a temporary jimmy rig so I can get it to my mechanic (who is nearly 300 miles away so it NEEDS to be driven there) and that along with the leaking clutch line can be repaired or replaced.

And yes I drive it perfectly fine on a daily basis on the leaking clutch. It's been leaking for at least 2 months. I just watch the fluid level and bleed the system when its looses pressure and stops functioning.

My 2 cents... If you want to chase 1 hp and .03 MPG at the risk of wasting bearings, go for it. Run the proper oil for the setup, period. As long as you're making 15psi at hot idle and 60psi at hot redline, experiment with some different weights.

I suggest, however, that you sneak up on it. Don't randomly dump in 0w20. The first time you drive it, you might do some massive damage. If it has 10w40 now, start by dropping to 5w30 or something.

My 2 cents... If you want to chase 1 hp and .03 MPG at the risk of wasting bearings, go for it. Run the proper oil for the setup, period. As long as you're making 15psi at hot idle and 60psi at hot redline, experiment with some different weights.

I suggest, however, that you sneak up on it. Don't randomly dump in 0w20. The first time you drive it, you might do some massive damage. If it has 10w40 now, start by dropping to 5w30 or something.

If you read the post above yours you will find that I have already decided. It has ran 5W-30 (manufacturer's recommended) conventional oil its entire life, so what I decided to do is keep the 5W-30, but I upgraded from normal conventional oil to 100% full synthetic extended performance by Mobil 1 (the best and most expensive oil on sale today so far as I can see).

If you read the post above yours you will find that I have already decided. It has ran 5W-30 (manufacturer's recommended) conventional oil its entire life, so what I decided to do is keep the 5W-30, but I upgraded from normal conventional oil to 100% full synthetic extended performance by Mobil 1 (the best and most expensive oil on sale today so far as I can see).

Pointiac Fiero- I almost bought one for my daughter
pathetic- my 64 Corvair handled better and was quicker

let me see if I have this right-
was a rear engine mounted system- that was loud- no get up and go
squirrely on anything but flat smoothe blacktop
any you took that engine/transmission out and swapped if with WHAT

I worked for Mobil Oil when Mobil 1 came out- Mobile/we, never recomended you substitue our thin synthetic on anything but a real tight engine- and that engine most likely would leak or use Mobil 1

Engines now days are designed differenty-
to an engine builder- the 80's engine to the now 2000 engines- are real different- now we can use thin oil/ before we could not-
simple- do you who think you know oil and viscosities- know why todays engines do well on thin oil

30 years ago- you put in this thin oil- you could expect a hole in your block-

and less you feel you know engines and clearances
muscle cars in the 70's ran on what oil- and how much HP/TQ
do you even want to know crankshaft/connecting rod clearances
you ever cared to see what specs an engine(any engine) shows and why