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High oil temp, low oil press. WTF?

dmd

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My car ('88 with 350 GM crate ZZ430 w/ '91 TPI) has been down for about four years during a long-term project to upgrade to headers. Once I got it back up and running in February, I noticed my oil temp gage was running high. It would start out normal for the first few minutes, but then would start climbing rapidly all the way to the peg at what I guess is about 320 degrees F by about 10-15 minutes from start. I couldn't rationalize this because coolant temp is running perfectly normal at 190 or so. I figured maybe it's the headers since the sensor is right underneath them, and I need to think about making a heat shield for it or something. But I also looked back at my maintenance logs and discovered I hadn't changed the oil on this car since '07, but haven't put even 1,000 miles on it since then either. Nevertheless, new filter and new synthetic 10W-30. Been driving it to work every day and checking the oil on the stick. Crankcase isn't smoking, smells normal, all seems fine. 20-minute drive to work every day, mainly been driving this car. Not sure what to think, but the drive is short enough that I don't think I need to worry.

Then today I noticed, about 1,000 miles from the last oil change about 2 months ago, that my oil pressure had dropped to the very top of the red zone, about 1/4 of the gage, what I assume is about 20psi. It usually runs around 40-50psi. Thinking that it might be the oil thinning out too much from the temps, I changed it tonight to Mobil 1 10W-30. It's still just barely above the red, maybe 25psi cold.

Total miles on the motor 23k. Running perfectly otherwise. I'm suspecting rod bearings. Any other diagnostics I should try or things to check before tearing down the bottom end, or is it not quite time to freak out yet?
 

Hib Halverson

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Answer me one question...

I recall that an '88 has the digital IP. I can't remember if that has the ability to display oil temp, if not and your gauge, which I presume is an aftermarket gauge, is pegged at 320°F, that's way into the danger zone for a petro-based oil and dangerous for Mobil 1.

At first I was thinking you need to test the oil temp gauge sensor to verify the gauge is accurate but then, you say that once the engine warms, the oil pressure is low. That would indicate the oil is really hot.

You also say that you assume the oil pressure is 20 psi...again, if you have an '88, with the digital dash, one of the digital displays should give you the exact oil pressure.
 

dmd

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I never said it was an '88 Corvette. The gages in it are all analog. It's just easiest to think of this as an OBD-1 LT4 engine with TPI, because the car is a hybrid of so many things that I don't want anyone losing sight of the forest for the trees, know what I mean?

The oil pressure is now low regardless of warmup time, even at startup. That's why I'm so concerned.
 

dmd

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Good news, I found metal chunks in the oilpan when I drained it.








It's UPGRADE TIME! :happyanim:
 

Hib Halverson

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I never said it was an '88 Corvette. The gages in it are all analog. It's just easiest to think of this as an OBD-1 LT4 engine with TPI, because the car is a hybrid of so many things that I don't want anyone losing sight of the forest for the trees, know what I mean?

Ok. I was confused by your OP. I thought the car was an '88.

My car ('88 with 350 GM crate ZZ430 w/ '91 TPI)
(snip)
 

dmd

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Ok. I was confused by your OP. I thought the car was an '88.

Yup, it is... full disclosure, it's an '88 Fiero with an SBC V8 conversion. Again, like I said, didn't want anyone to lose sight of this being an engine problem, but now that I've figured it out, there it is.

This happens at a somewhat disappointing time because I just got the bastard running right with the new headers after 4 years, but I am psyched because I just found a local builder who specializes in short-stroke SBCs who has an extra .060-over 400 shortblock he wants to unload. So this just became my new 6.8-liter ZZ430 project. And it's hard not to be a little excited about the prospect of a 413 cube SBC that turns nine thousand RPM in a badass little Fiero, even if it was borne of a chunk-spewing bearing failure.
 

Hib Halverson

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88 Fiero...last of the breed and the best of the platform.

Questions:

How do you get the car to hook with that much motor in it?
What transaxle are you using?
How do you get a ZZ430 to turn 9000 RPM?
 

dmd

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Great questions Hib, I get asked that a lot. As far as traction goes, there are two mechanical reasons that a Fiero has inherently better traction properties than, say, a car with a front engine/rwd layout. The first is the most obvious - with the rear-mid engine configuration, the most significant mass of the whole car sits directly over the rear wheels. The second, less-obvious reason is that it is transverse. Rather than the engine's torque trying to twist the frame of the car on the longitudinal axis, it twists it on the lateral axis instead. Think about that for a moment. What's great about a rwd configuration? Weight transfer. What's great about a transverse, rear-mid engine rwd configuration? Weight transfer amplification through the lateral axis. Bottom line: the more torque you give it, the harder it plants the rear tires in conjunction with weight transfer.

I am using a Getrag 282 5-speed transaxle on mine. I finished building this car in 2002 and it has held up with the reinforcing modifications I made to it. It's also all solid-mounted.

As for making it turn 9000rpm, I'm dreaming big. But big-bore, short-stroke is the path to that goal.
 
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Hello,

400 small block bored 60 over! Run away fast and don't look back. The absolute maximum overbore on any factory block 400 Chevy is 30. Twist it to 5K and the paper thin walls will split wide open. PERIOD! That's why your friend still has it. End of discussion.
 

Hib Halverson

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Great questions Hib, I get asked that a lot. As far as traction goes, there are two mechanical reasons that a Fiero has inherently better traction properties than, say, a car with a front engine/rwd layout. The first is the most obvious - with the rear-mid engine configuration, the most significant mass of the whole car sits directly over the rear wheels. The second, less-obvious reason is that it is transverse. Rather than the engine's torque trying to twist the frame of the car on the longitudinal axis, it twists it on the lateral axis instead. Think about that for a moment. What's great about a rwd configuration? Weight transfer. What's great about a transverse, rear-mid engine rwd configuration? Weight transfer amplification through the lateral axis. Bottom line: the more torque you give it, the harder it plants the rear tires in conjunction with weight transfer.

I am well schooled in all that theory. Back in the day, when I did a lot of road test work, I spend a lot of time in an '88 Fiero...the only model year that really handled and braked well. But still, with three times the horsepower, I'm curious how you launch the car in a quarter-mile pass and what tire do you have under it

I am using a Getrag 282 5-speed transaxle on mine. I finished building this car in 2002 and it has held up with the reinforcing modifications I made to it. It's also all solid-mounted.
Give me an idea of the reinforcing mods you made to the MG282.

As for making it turn 9000rpm, I'm dreaming big. But big-bore, short-stroke is the path to that goal.

You'll need a lot more than big bore, short-stroke and a 400 block if you want to turn 9000...reliably.

Hello,

400 small block bored 60 over! Run away fast and don't look back. The absolute maximum overbore on any factory block 400 Chevy is 30. Twist it to 5K and the paper thin walls will split wide open. PERIOD! That's why your friend still has it. End of discussion.

I guess I didn't catch the .060 over part in an earlier post. "Padgett, Daniel" is spot on. The only thing to do with a .060-over 400 block is to use it for scrap, or maybe to educate machinists on what not to do. Heck even going .030 with that block would require one that sonic checks perfectly, has no core shift and be used in a modest power, low RPM application because of the very thin walls.
 
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dmd

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I don't drag race anymore, Hib. This car is all street driven. It has 235/40 series Falken FK-452's on 18's.

The 282 runs RP synthetic fluid and has output shaft support bearings and no rubber mounts. This keeps the aluminum case from cracking and helps the spider gears survive the added loads.

So the 413 @ 9000 was a bit unrealistic, I am debating now between a 377 revver and the 413 low-rev. The 282 has short gearing so I need the revs more than I need the big torque, but as it's a street car maybe I am better off without them. This car is no lightweight anymore - 3130lbs on the scales - so it could certainly use the torque, but a 413 may be too much of a good thing for it.
 
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Performance

I don't drag race anymore, Hib. This car is all street driven. It has 235/40 series Falken FK-452's on 18's.

The 282 runs RP synthetic fluid and has output shaft support bearings and no rubber mounts. This keeps the aluminum case from cracking and helps the spider gears survive the added loads.

So the 413 @ 9000 was a bit unrealistic, I am debating now between a 377 revver and the 413 low-rev. The 282 has short gearing so I need the revs more than I need the big torque, but as it's a street car maybe I am better off without them. This car is no lightweight anymore - 3130lbs on the scales - so it could certainly use the torque, but a 413 may be too much of a good thing for it.

Have you thought about a turbo Regal 3.8 engine? Lighter and awesome performance. Tons of HP parts. You can get a high RPM engine just by installing a 283 crank in a 350 block. Receipe for a 327. Remember everything is a trade off. Torque is king if your drivetrain can stand it. Build for that and HP will come. Great choice with the '88 though. Smaller displacement will run cooler so keep that in mind. The camshaft should be mild for the street and the engine combination should match. No sense in a 3K little M block and 3K AFR heads for a 272 Mag. cam kit. Wasted money. Smarter not harder is the key. Drove an honest drag only car on the street and it was terrible. Constant tuning, no creature comforts (no vacuum from a radical camshaft), 8 light poles to a tankful of racing fuel, high engine temps. due to high compression, headaches from open exhaust, etc. 300 HP is the perfect number for the street from a V8 as it's a realistic goal and everyday/all day reliable. The choice is yours, but choose wisely. Decades as a Master Tech., restoring more collector muscle cars for people, and working on a championship drag team (2,500 + HP)
has taught me a thing or two about this subject, but that's just it; it's all subjective.
 

dmd

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Thanks for the suggestions Daniel, but it all may be moot. Wanted to update on this, the first thing was that once I removed the chunks I found in the oil and let the oil drain off of them for a day, they didn't look like bearing material at all. It was metal, but it was so fragile it crumbled in my fingers. Must have been random stuff that fell in the pan while I checked out other things, because none of it was shiny and there weren't any flakes in the oil.
Next, I have continued to drive the car and I noticed some strange behavior from the oil pressure gage. At startup it was showing 60psi at one point, then about 30 seconds later as I watched it suddenly, instantly jumped down to 20psi - making me almost certain this points to a gage or sender problem and not a real engine failure.

Then it turns out I have not one but two oil pressure senders. One runs the fuel pump through the ECM, the other runs the gage. So I'm checking the wiring and replacing the other sender later today.
 
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Yeah!

Outstanding! Truely happy for you. Make sure none of that gunk is blocking an oil passage or it'll be engine failure for sure.
 

dmd

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Thanks, it was great news for sure. Looks like that stuff was never inside the engine anyway, and I changed the oil, so no worries.
 

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