Slant Six Forum :: low oil pressure after cold start

Sniff the oil. Does it smell like gas? If so, gas dilution might make it into a lower weight. Can happen with a ruptured fuel pump diaphram.

Dirty oil filter? Not sure where the pressure transducer is. Speaking of which, can you swap in a known good oil guage? Like a mechanical one, just hold it in the engine compartment, to double check whatever gauge/tranducer that you are currently using.

How "long" do you need to make this engine go for? How long until the next oil change?

What brand and type of oil filter are you running?

An external coolant leak won't get into the crankcase.

Matt,

Bring it over to my place tonight around 7 PM and we'll take a look. If you don't want to drive it, we can chat by phone. I'll be home from work around 6. I have some inexpensive parts that may help you out. Might be worth a compression check before pulling the head to check shortblock condition. I have a comp guage if you need one.

Lou

Author:	red79 [ Fri Dec 02, 2011 10:08 am ]
Post subject:	low oil pressure after cold start
Just want to run a quick one by you guys. My slant is a 77, with 190k on the clock, never rebuilt. It has been making 45-50psi when cold and at running temp, and a min of 10psi idling in gear when very warm, such as after highway driving (10w-30). About par for the course for a worn in slant. This morning, I started the car after the coldest night we've had recently, plenty of ice on the windows after being on the street all night. Now it's having trouble making oil pressure, maxing out at 25psi at 3k rpm hot, and 5psi or less idling. My guess is the pressure relief valve got stuck after pumping that first slug of cold oil this morning. Is there anything else it could be? I've found the pressure relief valve servicing guide elsewhere on the forum, but I'd rather not go to the trouble of draining the oil if I don't have to. Thanks, Matt

Author:	supton [ Fri Dec 02, 2011 10:19 am ]
Post subject:
Sniff the oil. Does it smell like gas? If so, gas dilution might make it into a lower weight. Can happen with a ruptured fuel pump diaphram. Dirty oil filter? Not sure where the pressure transducer is. Speaking of which, can you swap in a known good oil guage? Like a mechanical one, just hold it in the engine compartment, to double check whatever gauge/tranducer that you are currently using. How "long" do you need to make this engine go for? How long until the next oil change?

Author:	red79 [ Fri Dec 02, 2011 10:34 am ]
Post subject:
Quote: Sniff the oil. Does it smell like gas? If so, gas dilution might make it into a lower weight. Can happen with a ruptured fuel pump diaphram. Dirty oil filter? Not sure where the pressure transducer is. Speaking of which, can you swap in a known good oil guage? Like a mechanical one, just hold it in the engine compartment, to double check whatever gauge/tranducer that you are currently using. How "long" do you need to make this engine go for? How long until the next oil change? I'll check the oil for gas ASAP, it's in the parking lot now and I can't take another 'lunch break' just now haha. I did check the dipstick though, and the oil level is good and looks quite new. I just picked up this car a few weeks ago to be my new driver. I changed the oil+filter 10 days ago, and have put about 800 miles on it since then, largely on the interstate at 50-70mph. When I changed the oil, I installed a cheap sunpro mechanical pressure gauge to replace the idiot light. That gauge has been the source of the numbers I quoted above. As for how 'long' I need the motor to run for, I picked up this slant hoping for a no-worries driver to get me to work, classes, etc. I've collected a pile of tune-up parts for this weekend, and rigged up an HEI system to go in at the same time, but I don't have the budget/spare vehicle to allow me to pull the engine or any similar downtime-intensive work.

Author:	SlantSixDan [ Fri Dec 02, 2011 11:18 am ]
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Yep, check for gas in the oil. Also it will be a good idea to service the oil pressure relief valve to make sure it's doing its job, as described in these two threads: thread 1, thread 2.

Author:	red79 [ Fri Dec 02, 2011 4:11 pm ]
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No gas in the oil as far as I can tell, guess it's time to clean the relief valve and see if that helps.

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Author:	red79 [ Mon Dec 05, 2011 2:04 pm ]
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I drained the oil then cleaned out the pressure relief valve yesterday, polishing the piston with crocus cloth as recommended. To keep the number of variables to a minimum, I poured the same oil back in (the oil was in the engine for less than 1k miles). Unfortunately, there was no change in oil pressure. When I drained the oil, it didn't smell like gas, and it didn't look cloudy, but the viscosity seemed low somehow. However, I just realized a leaking heater hose has started spraying coolant over the alternator and plug side of the engine. And today, when I pull the dipstick, there are a number of small 'droplets' all along its length, and occasionally a patch of white froth in the oil on the tip that looks suspiciously like water+oil. So, I guess my question now is: can you think of any way that I could be getting water in the oil as a result of my externally leaking coolant system? I'm replacing the heater hoses now, and I'm ready to drain and refill with fresh oil, but I'm worried that this is indicative of a busted head gasket. Thanks, Matt

Author:	SlantSixDan [ Mon Dec 05, 2011 2:21 pm ]
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What brand and type of oil filter are you running? An external coolant leak won't get into the crankcase.

Author:	red79 [ Mon Dec 05, 2011 5:20 pm ]
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Quote: What brand and type of oil filter are you running? An external coolant leak won't get into the crankcase. Figured as much. The oil filter is a bog standard purolator. Now there's a good bit of white 'smoke' coming out the exhaust when idle, and the coolant has gone gray-green. Guess the head gasket has had it.

Author:	SlantSixDan [ Mon Dec 05, 2011 5:46 pm ]
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Sounds like it. At 190k miles, this is gonna be a tired pony. Probably over/due for a complete overhaul.

Author:	red79 [ Tue Dec 06, 2011 8:16 am ]
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The story just keeps getting better. Found some oil pooled in the air cleaner this morning. Normally this would suggest rings to me, but I watched the pcv hose for a few minutes and nothing was coming out besides a light mist. Could this be another symptom of the failed head gasket, or is it a sign of something else on top of that?

Author:	Reed [ Tue Dec 06, 2011 8:30 am ]
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Pooled oil in the air cleaner usually comes from the mist from the PCV valve and is a sign of excessive blowby due to worn rings and/or piston bores.

Author:	red79 [ Tue Dec 06, 2011 9:53 am ]
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Well since this is my driver and I don't have the luxury of a complete overhaul right now, I'm going to swap in a new head gasket next weekend and see how many more miles I can put on it before compression gets too bad. Ordered the fel-pro gasket set, should be here by friday. Will I have any problem pulling the head with the manifolds still attached? I know it's not the way outlined in the FSM, but I'd really rather not complicate the job with seized then broken manifold bolts. I've got a cherry picker so I won't break my back, anything else I'd need to worry about?

Author:	Dart270 [ Tue Dec 06, 2011 10:08 am ]
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Matt, Bring it over to my place tonight around 7 PM and we'll take a look. If you don't want to drive it, we can chat by phone. I'll be home from work around 6. I have some inexpensive parts that may help you out. Might be worth a compression check before pulling the head to check shortblock condition. I have a comp guage if you need one. Lou

Author:	KBB_of_TMC [ Tue Dec 06, 2011 10:14 am ]
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I don't know if this applies to a /6, but my Mopar 383 developed a very intermittent zero oil pressure problem; the cause was very hard to find. It eventually turned out that the oil pump drive shaft worked loose from its gear such that most times it would work fine and only under a rare circumstances would it stop turning the pump, but keep turning the distributor. You might look for something like that while you have your /6 out.

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Author:	red79 [ Tue Dec 06, 2011 10:42 am ]
Post subject:
Quote: Matt, Bring it over to my place tonight around 7 PM and we'll take a look. If you don't want to drive it, we can chat by phone. I'll be home from work around 6. I have some inexpensive parts that may help you out. Might be worth a compression check before pulling the head to check shortblock condition. I have a comp guage if you need one. Lou Thanks Lou, I'll stop by tonight. As for intermittent oil pump gear engagement, wouldn't that cause my pressure to fluctuate intermittently? It's well behaved, just too low.