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Oil pressure low until engine warm


Bryan G
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Before I dig too deep, advice?

 

Bone-stock '51 Fordor with the "Lion-Heart" 226 flathead six. (No sarcasm: a great engine!) Doesn't burn oil and has always had strong pressure, cold or hot. I'm not sure accurate the factory gauge is but cold idle would normally show 20lbs, cold at highway speeds 60lbs, hot at highway speeds 40-50lbs. Until recently. All of a sudden it started this: cold start, needle goes to about 40 but then drops to about 10 or less and regardless of engine speed it lingers low, gradually increasing as the engine warms up until it finally reaches mid-range. If I shut it off and fire it back up warm it reads mid-range again but cooled off some it is low. 

 

I cleaned the connection at the sending unit. I was going to pull it off tonight and try rigging up an aftermarket unit (electrical type) that I have in my junkbox, but that sender is on there but TIGHT. Meanwhile, I'm do for an oil change and I hate to do it if I need to drop the pan soon. So, before I start pulling things apart and swapping parts, has anyone run into this? I know the sending unit is the easiest place to start, of course.

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They are great engines!  My first car was a 1948 Ford 6, first year of distributor in conventional location.

 

Your issue sounds to me like a clog somewhere in the oiling system:  Cold oil = thicker and doesn't flow as well; warm oil = thinner and flows better.  I don't remember enough about that engine, but suggest you see if you can find an oil flow diagram and address the easy parts first, starting with flow to the sender.  I don't even remember whether the sender is electric, or there's a Bourdon tube of oil to the gauge.  If the latter, I'd start there.

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1 hour ago, oldford said:

"DebbieDowner"???

Yes, the one person who says it’s not looking good or in this case I had that problem too and my engine blew up kind of news when everyone else says it’s no big deal.  That’s a definition of DebbieDowner in these parts.

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With the limited amounts of information I had a s very similar problem. Running to heavy oil engine with a very good lower end  progress relief valve was stuck closed in the oil pump   had real high oil pressur  un till the oil filter material collapsed then very little oil pressure

Just a . Though. 

 

 

 

 

 

 

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1 minute ago, Mikefit said:

With the limited amounts of information I had a s very similar problem. Running to heavy oil engine with a very good lower end  progress relief valve was stuck closed in the oil pump   had real high oil pressur  un till the oil filter material collapsed then very little oil pressure

Just a . Though.  Ops not a full flow filter system on this engine.  Sorry. 

 

 

 

 

 

 

 

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Posted (edited)

Some good suggestions; I should have mentioned, this uses an electric sender. I really need to buy a cheap mechanical gauge just as a check (I've needed one before). I did notice that in the weeks before this happened the pressure was reading higher than I'd seen it before (though not pegging the needle or anything like that.) I did contemplate the filter being an issue but as others pointed out, it's not full-flow so I discounted that notion. (I wasn't happy with that last filter I installed-I tried a Luber-Finer rather than my typical Wix/NAPA or Hastings. It was paperboard where the others were steel.) As for the oil, I'm running a non-synthetic 10w30.

 

Guess I need to study up on the pressure relief valve, how to access it, etc. Time to dig out the shop manual. And, Cranbrook, I don't mind you offering up that advice. I'm ever learning. While I'm driving this car I'm doing a truly redneck driveway-rebuild of a straight eight Chrysler. I've experienced an amazing number of firsts this spring, having never had an engine apart before, and it's all thanks to the advice gleaned from this and other forums (P15-D24 especially). 

Edited by Bryan G (see edit history)
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Posted (edited)

Solved; my am I embarrassed...and perplexed.

 

Naturally I check the oil level regularly, and when the pressure started acting strange I checked it right away...yep, just fine, about 3/4 quart low (because 3 cups sounds funny when it comes to motor oil!) I checked again a few days ago and it hadn't moved. Yes, same dipstick as always, ever reliable. Same dipstick since some fellow at Rouge stuck it in there. Never an issue in the 10 years or so I've owned the car. Tonight I changed the oil.

 

The dipstick lied. I have no idea how. I drained an astonishing amount of oil out, less than 2 quarts. Ouch. How could I do this? 

 

After the change I fired it up and the pressure was normal, of course. Fast idle was nearly 40lbs on the gauge. Hopefully this tough old 6 is no worse for the wear. Checked the dipstick after she cooled down, yep, right on the money. From now one I'll check it constantly and keep it topped off. 

 

I have to relate another time a dipstick lied to me; I can't explain that one, either. Someone gave me an old boat with a Mercruiser inboard/outboard, basically a Pontiac Iron Duke. I went to change the oil but didn't know how much it would take so I went to the store and bought 5 quarts and a filter. After dumping it all in I pulled the stick: nary a drop! Back to the store, dumped it in, still nothing! I figured, well, they build marine stuff extra-tough so I guess it has a lot more capacity. "Full" didn't come until I dumped in the TENTH quart. I fired it up and in a minute it started running funny and oil actually started coming out of the breather (on the carb!) Guess it overwhelmed the PCV. I let it cool down and when I pulled the dipstick the level was now almost up to the handle. But, where was it hiding before? Still haven't figured that one out.

 

Now you fellas know why my wife won't let me work on her new cars!

Edited by Bryan G (see edit history)
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 Years ago a neighbor was changing oil in a 60’s something car. Near new. He came over and said he’d put in 8-10 quarts of oil and it was just touching the the stick. Only called for 5 quarts. Wanted to know what I thought.

  I told him if it was mine, I drain the pan, put in 5 quarts, and then pull it off that 20% +/-  slope of a driveway he had and check it on level ground.

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Had a gentleman stop by with his older motor home Dodge Chassis. He hard just changed to oil put in the 6 qt called for in that he owners book he looked under the engine totally dry no oil leak or drips.  Found the dip stick tube rusted off at the pan and was just dangling in mid air.  

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