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Oil pressure drops completely after oil thermostat opens

GTX

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Apr 13, 2012
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Toronto, Canada
Hey gurus,

After engine rebuild and added an aftermarket oil cooler I see red light coming up after a few minutes of engine running. Obviously I shut the motor right off. Did not have a chance to install the proper oil pressure meter or do other diagnostics. So, I wonder if I did something stupid while engineering an oil cooler size or line size. The ones I use are AN6 and oil cooler is about over 24x12 inches. I was trying to replicate the OEM size, which I have seen only on pictures /ubbthreads/images/graemlins/smile.gif I dont want to risk running the engine with red light on in case the oil cooler is empty and requires time to fill in. What would you do in my case? I could install a bypass line or put the N/A oil filter plate back to eliminate the oil cooler completely. If I shut the engine off and let it cool, everything is normal. Engine starts, light goes off until it warms up again.

Thanks,
A
 

tektic

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What weight oil are you using? Balance shaft intact? Oil filter housing? Mods to oil bypass piston?
 
Last edited:

GTX

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Apr 13, 2012
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Toronto, Canada
Im thinking, its either bypass valve, or the fittings for oil cooler are too small. Only 3/8 opening on AN6 connectors. I need AN10.Syntetic 5w20 oil.
 

tektic

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Try 10w-30 I won't run anything lighter. The manual doesn't recommend anything lighter unless extreme cold.
 
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EMX5636

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I second what tektic said, I wouldn't run anything thinner than 10w30. As for the lines, most people run -8 or -10 lines to an aftermarket cooler. Did you fill the cooler before initial startup? Not usually necessary, but not a bad idea either.

Also 12x24 is huge. That's more of a trans cooler size. The OEM cooler is like 8x10-12" if I recall. You can get away with it, but you'll probably want to pre-fill it, as it will take a while to fill with oil initially. It will hold oil between changes, so no need to do it after the first time, or if draining the cooler.
 
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marvinmadman

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Nov 10, 2003
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What type of fittings you used? Is that the only connections you made or moved on the OFH?
 

GTX

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Toronto, Canada
The fittings are AN6 for pipe of 3/8 in size. I did not pre-fill the radiator, will try now and see what happens. The good news is that while it is cool, the oil flows normal. I wonder if by-pass valve can make anything funny. if it gets stuck half way, I'd have two passes for oil to escape, then I have a pressure drop, but it should be only temporary. Anyhow, installing pressure gauge now, will see better, what is going on.
 

swe_gvr4_1991

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Sounds like the thermo just opened and the oil flow went into the oil cooler and simply triggered a low oil state light.
Check the level just after the light comes on. Engine off. Then recheck after a few minutes to see how much the level rises.
You should lose some oil when engine i pumping oil into the empty cooler since the cooler needs to be filled initially.
What way is the cooler mounted?
 
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GTX

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Guys, you will not believe what was wrong. I managed to put an absolutely fully functional oil pressure sensor, but from N/A engine. This is really weird. As it heats up the light goes on. I had an oil pressure gauge connected in parallel and seen oil pressure go up normal, but the sensor would not turn the light off. As soon as I put the sensor from Turbo engine, everything went back to normal. How could it happen? Do N/A and Turbo engines have different pumps and oil pressure? Hence different sensors?
 

swe_gvr4_1991

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I know they look totally different. Can you post up pics of them?
Trying to find the rated pressures. One of them opens up at 7 PSI or close to that.
 

tektic

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ronkonkoma, ny
If you realy think the oil pressure light sensor is the problem a new one is like $6 from rock auto. Part found here

If I put 5w30 in my old talon the light would come on as soon as it warmed up. Also are you using almost a whole extra qt of oil now that you have such a huge cooler?
 
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iceman69510

Turn Right Racing
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Wondering that too. How much oil in the system?
 

GTX

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Apr 13, 2012
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Toronto, Canada
The cooler is not that big, it is very slim. I think I gave you the wrong dimensions. I also pre-filled it. The issue is with the sensor, for sure. The car is running fine now and oil pressure is about 20-25 at 1k and goes up with rpms all the way to 60 psi. Not pushing the rpms now though.
 

GTX

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Toronto, Canada
Not without your help, Corte! Many Thanks!!! /ubbthreads/images/graemlins/smile.gif
 
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