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Old 06-12-2018, 11:33 PM
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Default SC2 ͏O͏i͏l Pressure Loss

Hi,
Iím new to the thread. I have a 1998 SC2 that I ra e in 24 hours of Lemons. My first engine lasted about 3 laps before ͏o͏i͏l pressure started to drop and then before I could get back to the paddock the engine had a tapping sound. When I shut it off it wouldnít restart and I found the crank position sensor to be bad, I replace it and it started back up but had a tapping sound. I replaced the 3ngin3 with an 80K mile junkyard engine with 185+ compressions and it did the exact same thing on the track but this time made 7 laps. Neither engine overheated, confirmed with infrared thermometer immediately on head temp of 210 after pitting. Any idea on what is causing an oil pressure drop to 15 to 20 psi followed by loss of power after working the engine around peak torque range for 15 minutes and driving a CPS failure and internal tapping noise?

Thanks,

Dave
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Old 06-13-2018, 01:05 AM
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1) What weight oil are you using?
2) Is the oil light on the dash coming on -- meaning is that how you are determining the oil pressure drop? Or are you determining it another way?
3) Assuming you start with the engine full at 4 qts of oil, what is the reading on the dipstick when it craps out?

I suspect the CPS failure is heat-driven. You are essentially melting the coils inside it.
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Old 06-13-2018, 05:08 PM
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Iím using Pennzoil high mileage 10W 30, oil light never came on, Iím reading ͏o͏i͏l pressure from a mechanical ͏o͏i͏l pressure gage I installed, engine oil was still on full after failure (both engines) with no water in the oil or oil in the water. Also, compressions are still good on the failed engines and plugs all have a slightly brown tint to them...as they should look if itís running right.

Mods Iíve done is straight pipe exhaust and no cold air intake sensor as Iím running a cold air intake and didnít reinstall that sensor, and Iíve removed the thermostat to make the engine run cooler. I donít know the ͏o͏i͏l temp but I know it hasnít overheated and I checked the head temp at shut down at 210 with an infrared thermometer. I also installed a new water pump.
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Old 06-14-2018, 01:26 PM
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Believe oil cavitation, runaway oil temp due to insufficient cooling ability of cooling system as configured, and insufficient oil flow per unit per unit time may be to blame.

Oil temp increases with oil pressure. These cars do not have a dedicated oil cooler. I suspect that the cooling system cannot remove the additional heat from the oil efficiently enough. That's why the car does not appear to be overheating in the traditional sense. But if it is hot enough near the crank to thermally destroy a ckp, it's too hot.

The cavitation will cause bubbles in the oil, which seem to take the biggest toll on the connecting rod bearings which which will wear and eventually lead to a knock or a seize. I surmise that bad enough oil cavitation will actually lead to a situation where the oil pump is trying to pump foamed oil instead of liquid causing the oil pressure to drop. That obviously means oil starvation at various parts of the engine.

A dead CKP in an S car means no spark and no fuel, and therefore a shutdown. An overheated ckp may recover to the proper resistance to send the signal of pulses that the PCM expects. Thus if you wait and let the car cool down, it may start and run again. If the coils in the ckp are melted, it will obviously never run. Don't know how long it takes the oil bubbles to disappear if they do.

Cavitation minimizing high volume oil pumps are out there even for s cars. I'm sure external oil coolers exist as well. I'm not sure how stock stock has to be for your racing but neither an oil pump change nor an oil cooler change are performance enhancements.

The heat may also be breaking down the oil itself. You'd have to pull some after one of these events and do a first-order visual comparison to new oil at a minimum.

If the car's stock cooling system was sufficiently efficient at removing the additional heat from the oil, I believe the car probably would overheat in the traditional sense.

Another angle to consider this from is to think about what in the car is not changing when you replace the engine. First on my list is the radiator. Be sure you are getting maximum flow through the radiator and consider one with increased volume and flow. Since the flow is limited by the water pump, you may need to invest in a a higher flow water pump.

Please be aware I have zero experience in racing s cars. The above comes from researching your issue on the web and putting two and two together which may add up to 4 or it may add up to 5.

I suggest researching the things I have mentioned independently before you spend a dollar. My response is based on logical speculation. It explains what you see. But that does not necessarily make it correct. Spend money at your own risk after your own research. I hate to give advice to people that unnecessarily costs them money because it is wrong.

Also realize that the ects needs to be the second design all brass tip and sourced from GM not a parts store. And remember that that temperature measurement is being taken in a coolant channel in the head, not down by where all of the excess heat is being generated. That means the air-fuel mixture may get excessively rich because the ects is sending a systematically low temperature to the PCM which does not reflect the true engine operating temperature in this case and will lead to an overly Rich fuel mixture for the situation.

Just my two cents
I drive a 97 SC2 so I am very interested in the results.

Please be kind enough to come back and let us know how you solved the problem.

Last edited by derf; 06-14-2018 at 01:34 PM.
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Old 06-14-2018, 01:33 PM
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So why do you think the CPS failures are heat related if the engine hasn’t overheated? Thoughts on what is causing the loss of ͏o͏i͏l pressure. I’m assuming me not shutting down the engine soon enough with low oil pressure has caused the internal knocking. Will CPS failure cause loss of ͏oil pressure? Two engines failed exactly the same at about the same time under the same conditions, the exact same way and the only common components are the ECU, radiator, and exhaust. Recommendations?
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Old 06-14-2018, 01:39 PM
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Thanks Derf, I also suspect you may be right. Your post came thru after I posted my previous one.
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Old 06-14-2018, 01:39 PM
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The excessive heat is in the crankcase. The CPS is monitoring the rotation of the crank. You are locally overheating the oil. This does not have to necessarily overheat the entire engine. I believe it to be a runaway temperature increase which is counteracted in no way by the cooling system in place. Therefore the coolant never gets hot enough for the entire engine to overheat in the traditional sense.

My recommendations are all listed above.
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Old 06-14-2018, 03:48 PM
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You are quite welcome. People on the Forum ask me all the time why I bother to research other people's issues on my own time. The answer is that I love to learn and if it helps someone at the same time then that is also a plus. It drives me to learn more about my vehicle and even though I have driven Saturn as cars since 1992 exclusively, there is always something new to learn
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Old 06-14-2018, 08:33 PM
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Cars should never be run without a thermostat OR a restrictir. We ran a plate with a 5/8” hole in our 800 hp stock car in Bakersfield Ca. Air temp was 100+ coolant was 210. With no thermostat or restrictor the water flows too quickly through the radiator and does not transfer heat through the fins to the air. I hope this makes sense. The oil is another story, the car probably needs a windage tray to keep the crank from aerating the oil.
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Old 06-14-2018, 08:44 PM
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Been waiting for you to weigh in, Andy...
​​​​​​ Why is the water pump not the limiting factor in the rate at which the coolant ciculates?
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