Oil Pressure Questions

[Super_Dave]

My project build has a fresh, fully rebuilt 355 SBC with around 3K on the odometer. I have installed a performance built 700r4 and my mileage dropped from 11.5-12 to 7-7.5 mpg.

It was suggested that the temp might be a contributing factor. The temp gauge (new Speedhuts) pegged at around 155°-158° so, I checked the T-Stat (new STANT) and decided what the heck, and replaced it with a new 190° unit of better quality. The engine now runs around 185°-190°.

The same day I replaced the T-Stat, I let it warm up and then took it for a spin to bring it up to full operating temp. After a 5 mile jaunt, I got back home and had a definite lifter tick. The oil pressure, which was always around 40# +/- at idle, had dropped to 10#-15#. Pressure is fine under load.

So, I replaced the oil with 10/40 and added a Zinc additive and the pressure went from 15# to 25#, still quite a bit lower than before the the T-Stat switch.

So, from what I have read, 10# at idle isn't something to worry about. However, a 30#-35# drop still seems a bit weird. Makes me wonder if I might need another new oil pump.

Any thoughts or comments regarding the T-Stat and operating temp driving the pressure down or upgrading the oil pump?

SD

[68gmsee]

Yeah, that's quite a drop. Thinning of oil due to higher temps could contribute to it. Since the only thing you did was change the t-stat it's easy enough to put the old t-stat on it to see if the pressure goes back up.

There's a possibility, since it's a fresh built motor, that something may have decided to go south on you but I've never experienced an oil pump going out that fast.

[Super_Dave]

I also think I might have a choke issue where I might be running some raw fuel down the carb and diluting the oil over time. I have no gas leaks anywhere. . . quadruple checked everything. . . but continued to smell gas every time I shut it down after a drive. . . and the addition of a 700r4 transmission cut the mileage by 40+%. . . which is still needing to be resolved. I am hoping it might just be a shift point adjustment, but I don't feel too confident about that.

[geezer#99]

What carb?
What's rear gear ratio?

[Super_Dave]

Edelbrock Performer Air Gap

Edelbrock 600 CFM, ELECTRIC CHOKE
(CALIBRATED FOR FUEL ECONOMY)
Calibrated for maximum fuel economy. Includes timed vacuum ports, EGR and fuel vapor outlet. Not for computer-controlled engines. Comes with the following jets, rods and springs: Metering Jets - Primary .098, Secondary .095; Metering Rods - .073 x .047; Step-Up Spring - orange (5" Hg).

14 Bolt with 3:73's.

[geezer#99]

You need a fuel regulator set at 5 psi for your eddy carb.
The airgap doesn't help with mileage either. It runs too cold.

Have you tried a mileage test by just driving in 3rd gear? Stay out of overdrive.
What's your initial timing?

[Super_Dave]

Originally Posted by geezer#99

You need a fuel regulator set at 5 psi for your eddy carb.
The airgap doesn't help with mileage either. It runs too cold.

Have you tried a mileage test by just driving in 3rd gear? Stay out of overdrive.
What's your initial timing?

I was going to get the Edelbrock fuel pump that is supposed to have the 5 psi built in. . .
I have not run in third gear only. . .
Initial timing is 12°. . .

I was thinking about changing out the Air Gap with the top end rebuild. Also getting away from the flex fan with an electric water pump and fan setup, equal length long tube headers 1 5/8 or 1 3/4 primary (toss the Heddman Shorties used on my International swap) into 2.5" secondary pipes and 3" exhaust to improve cylinder evacuation.

Since the machine shop dicked me on parts of the build, I want to R&R the top end before I have any catastrophic issues. A different brand name Cam (Comp EX268H-10), better lifters, roller rockers on different heads (something along the Blueprint H8002K's or comparable. . .) Edelbrock Performer. . .

and if I want to go all in, an FiTech GO EFI 4 https://www.youtube.com/watch?v=2bhT0Lg2yRo

or Go Port EFI 550 http://fitechefi.com/products/goport/ in place of the Edelbrock 600.

With FiTech, you only pay for what you want and save a boatload of money, opposed to paying for the other brands who sell everything in one package. . . whether you need it or not. Plus they have years of OEM EFI background.

[Ken B]

I don't think the new t-stat is your problem, coincidence more than likely. 190 degrees is exactly where you want to be running. If putting that new t-stat in caused your oil pressure to drop and a sudden lifter tick then you've got bigger problems.... I recently installed a new GM crate engine in my 70 Longhorn. 190 degree t-stat. I always have 30 pounds at idle and an easy 65 pounds while cruising down the road with 4.10's. I run 10w30 Penzoil dino oil...

[cadillac_al]

Yeah, I would be more concerned about the oil pressure issue than the running and fuel mileage issues. Is it a known dependable gauge or a new one?

[Super_Dave]

Originally Posted by cadillac_al

Yeah, I would be more concerned about the oil pressure issue than the running and fuel mileage issues. Is it a known dependable gauge or a new one?

I agree.

Yes. . . Speedhut analog gauges. Work great so far.

[Super_Dave]

Originally Posted by Ken B

I don't think the new t-stat is your problem, coincidence more than likely. 190 degrees is exactly where you want to be running. If putting that new t-stat in caused your oil pressure to drop and a sudden lifter tick then you've got bigger problems.... I recently installed a new GM crate engine in my 70 Longhorn. 190 degree t-stat. I always have 30 pounds at idle and an easy 65 pounds while cruising down the road with 4.10's. I run 10w30 Penzoil dino oil...

That's right where I "was" running. . . so I think I need to take a serious look at the top end and the oil pump. The "builder" (a machine shop that successfully races and produces race engines locally) seems to have used some questionable parts rather than brand names. He says he "can;' recall" what he used in my engine. I absolutely DO NOT feel comfortable with where things are, so I might as well bite the bullet and redo the top end and oil pump. . .

[Dead Parrot]

Didn't see what oil you started with. In my mostly stock crate 350 with 90k+ miles, I run 10W-30 and a 195* Tstat. On the 40+ year old mechanical oil pressure gauge, once hot, usually see about 15~20psi at idle and 40+ at speed.

If you are worried about low oil pressure, add an idiot light sensor and light as an attention getting backup.

A t-stat normally starts opening at the listed temp so your engine with a 190 is likely running at 205-215. Most temp gauges are doing good to be within 5% of actual reading.

What RPM are you at when at 60mph?

Before tearing the motor apart to change oil pumps, might swap oil gauges and senders to verify your readings. Would suck to find out after a new pump that your gauge was bad.

[Super_Dave]

Originally Posted by Dead Parrot

Didn't see what oil you started with. In my mostly stock crate 350 with 90k+ miles, I run 10W-30 and a 195* Tstat. On the 40+ year old mechanical oil pressure gauge, once hot, usually see about 15~20psi at idle and 40+ at speed.

If you are worried about low oil pressure, add an idiot light sensor and light as an attention getting backup.

A t-stat normally starts opening at the listed temp so your engine with a 190 is likely running at 205-215. Most temp gauges are doing good to be within 5% of actual reading.

What RPM are you at when at 60mph?

Before tearing the motor apart to change oil pumps, might swap oil gauges and senders to verify your readings. Would suck to find out after a new pump that your gauge was bad.

I was running 10/30 for the past 3500 miles. Just switched to 10/40 and a Zinc additive.

At 60mph, I am turning 1,800 rpm.

I shot the block in several places with a laser temp gun and got back a 190°+/- reading, so I believe the gauge to be correct. The oil pressure gauge put out 60#+/- at cold idle and cruising speed.

With the 10/40 I now get 25#+/- at hot idle. The hot idle seems to have also dropped to around 250-300 from the 700+/- it was before, so that may be part of the issue with the drop. . .

Need to check the idle circuit settings and get it back to 500-700 hot.

[Dead Parrot]

Just an odd thought. Make sure the electric choke is working. Might explain why the 190 T-stat caused the idle drop. If the choke isn't working, or is adjusted just a little off, the higher heat from the new T-stat could have caused the carb to come off cold(high) idle. Long shot but doesn't require new parts to check.

Maybe my 1405 Edelbrock carb is weird but have never used a regulator and it is on its 3rd mechanical fuel pump. Worked fine on all of them. I did set the float level before installing.

On the mpg question, is the installed cam designed to be effective at 1800? Maybe your 'professional builder' built you a race track motor that wants to run at high RPMs.

[Super_Dave]

Originally Posted by Dead Parrot

Just an odd thought. Make sure the electric choke is working. Might explain why the 190 T-stat caused the idle drop. If the choke isn't working, or is adjusted just a little off, the higher heat from the new T-stat could have caused the carb to come off cold(high) idle. Long shot but doesn't require new parts to check.

Maybe my 1405 Edelbrock carb is weird but have never used a regulator and it is on its 3rd mechanical fuel pump. Worked fine on all of them. I did set the float level before installing.

On the mpg question, is the installed cam designed to be effective at 1800? Maybe your 'professional builder' built you a race track motor that wants to run at high RPMs.

Yeah, I need to look at the choke for sure. Ran again today and it drops to around 250-300 at idle.

As far as the cam specs, the builder is clueless about what he spec'd and said "read your invoice." Well, it was a hand written receipt. The only way to check the cam is to pull the timing cover and look at the end of the bump stick. . . assuming the manufacturer marked the cam. . .

[geezer#99]

Guess what!!
The cams are marked but only on the back end!!

[Super_Dave]

Originally Posted by geezer#99

Guess what!!
The cams are marked but only on the back end!!

Maybe that's the problem. . . the cam is in backwards!!