3 400 questions
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3 400 questions
Hi,I would like to know what is good compression for a stock 400 motor.2nd question is I start up the engine and oil pressure jumps up and as the motor runs to warm temperature the oil pressure goes down to nothing.When you drive the truck when the motor is warm the oil pressure gets higher but drops again as you slow down.Should I be concerned about this?Whats the fix for this problem?And the last question is after I shut the motor off and turn the key back on quickly the engine "diesels".Is this a timing problem? Thanks for all the help Paul
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From: e-burg
ok first off compression it depends on the motor i would do a wet and dry compression check if the wet is close to the dry u should be ok. i would say any where form 100-140 would be ok. second oil pressure, these motors are plagued with low oil pressure ur problem sounds normall but i wouldnt worry about it ive known 400's to run for 150-200k on low oil pressure and be ok. 3 if u dont let the motor totally stop b4 u turn the key back on it will do this but if u turn the key off and it says running then its a timing issue
hope this helps
hope this helps
Last edited by good 'ol ford; Jan 31, 2005 at 08:52 PM.
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Just stuck my new gauges in my truck (78 f150 with the 400) Your oil presure seems the same as mine. 60 psi cold, 25-40on the highway,5-15 hot idle in gear. This is with 5w-30 oil. If the oil pressure scares you a little run thicker oil like 10w-30 or 15w-40.
MSEE
Joined: Apr 2004
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From: Austin, TX
As the others have been saying, the low oil pressure is pretty common on high mileage 335-series motors such as your 400. The most common thing to try first is step up your oil weight. Mine uses 20W50, and I also run STP oil treatment to help.
Dieseling can be a timing issue but there are actually many possibilities. The run-on happens because there is a way for air\fuel to get inside the cylinders, and a hot point that ignites it. Many 400's have an idle stop solenoid that holds the motor's idle speed while the engine is running, then when you shut off the ignition, the solenoid retracts and lets the throttle plates close.
Dieseling can also be caused by improper ignition timing, high idle speed, carbon buildup in the combustion chamber, low fuel octane, or a vacuum leak.
Dieseling can be a timing issue but there are actually many possibilities. The run-on happens because there is a way for air\fuel to get inside the cylinders, and a hot point that ignites it. Many 400's have an idle stop solenoid that holds the motor's idle speed while the engine is running, then when you shut off the ignition, the solenoid retracts and lets the throttle plates close.
Dieseling can also be caused by improper ignition timing, high idle speed, carbon buildup in the combustion chamber, low fuel octane, or a vacuum leak.
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Joined: Oct 2002
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I've been known to run 85-90W gear oil in these things in the Desert where I live to slow down the oil burning and stop the knocking at idle from worn out bearings. I don't recommend it, but I've done it. I usually run 10-40 if temps go below freezing. Otherwise I run 20-50 unless I'm racing or running hard pulling lots of loads. Then I go straight 50W racing oil.
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New User
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The reason why i was running 5w-30 was because my truck sits outside. I live in saskachewan canada and in the winter -40 isnt all that uncommon(we had a couple of days at -50 with the wind chill). In the spring i will change it out for 15w-40.
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Cargo Master
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From: NE Texas
You know, low oil pressure as long as it is not too low is not an altogether bad thing. Cummins actually regulates the oil pressure down to 15PSI, and their engines commonly go 1,000,000 miles between overhauls.
They say that high oil pressure only accomplishes higher fuel consumption because of the added energy that it takes to turn the oil pump.
The reason that you and I like to see high oil pressure is that it indicates that the engine does not have excessive oil clearance as it wears. If an engine, from its design, has low oil pressure when fresh with known good bearing clearances, then enjoy it and be happy.
I'm not suggesting that anyone run 15PSI oil pressure. I am suggesting that as long as the engine isn't worn out, don't worry about it.
Good luck,
Doc
They say that high oil pressure only accomplishes higher fuel consumption because of the added energy that it takes to turn the oil pump.
The reason that you and I like to see high oil pressure is that it indicates that the engine does not have excessive oil clearance as it wears. If an engine, from its design, has low oil pressure when fresh with known good bearing clearances, then enjoy it and be happy.
I'm not suggesting that anyone run 15PSI oil pressure. I am suggesting that as long as the engine isn't worn out, don't worry about it.
Good luck,
Doc
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Joined: Jan 2005
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From: S.C. North Dakota
I would ad a oil friction additive to your engine oil to help save on the wear
if your concerned about low pressure. Its good stuff and i use it although some of it is more expensive and it can stretch out oil changes more .
if your concerned about low pressure. Its good stuff and i use it although some of it is more expensive and it can stretch out oil changes more .
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