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289 A-code low oil pressure at idle

New User
Posts: 11
Joined: 05/11
Posted: 06/11/13 02:34 AM

I have 65 mustang GT and my oil pressure is high when i first start it.  Then when it warms up oil pressure is low.  Also when warming up car as a clacking sound from engine . I guessing i need to tighten my lifters on the heads or do i need oil pick up or ioil pump? Any advice?  

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New User
Posts: 33
Joined: 05/13
Posted: 06/11/13 05:11 AM

a few things... a mechanical test of the actual oil pressure..

Image 12200
Engine Oil Pressure Test Kit harborfreight Item #98949

if you visit junk yards once in a while.. you might want to pick up an oil sending unit extension off a mid 80s thru mid 90s 5.0 or 5.8W.. some others have them..  with Dual ports.. so you could run either your sending unit and the Hf pressure tester.. or directly mount an oil pressure gauge to the adaptor ...

do you have a remote starter switch... so you can lay under the front and crank the engine remotely... if so... block the wheels.. disable the ignition system. verify it will not start.. this is usually done by UNPLUGGING either of the small wires off the coil...  

remove the oil filter..  with a drain pan under the area.. crank the engine for a few seconds. how much oil flow do you get..  significant. or a trickle??  i don't know if your engine was rebuilt.. or if the early motors came with the aluminum bodied oil pumps..  if so.,.. you might want to install a stock replacement pump..  most engines don't need a high volume.. its exerts additional pressure on the distributer drive gears..

you might also want to stick a big socket on the crank bolt.. with a breaker bar.. rock the crank back and forth while watching the distributer.. if you get more than about 1/2" of movement at the outside of the harmonic damper before the distributor reacts.. perhaps you need a timing chain set..

low oil pressure will cause the lifters to make noise...

so fix the oil pressure issue first..

also.. what weight of oil are you running??
what temp thermostat do you have in it.. 180F??

overheating will thin the oil... reducing the oil pressure..  

Post Reply
Posts: 588
Joined: 07/06
Posted: 06/11/13 10:40 AM

Wayne is giving you a great start. You can't rely on a light on the dash or a factory gauge. You need to know the actual psi of the oil pressure your engine is being provided. High oil pressure when cold is normal and it will drop some when the oil is warmed up. There are a lot of variables, such as oil viscosity, oil pump pressure spring, pickup restrictions, ability of the oil to drain back to the sump properly, etc.

Unless you have a K-code engine with mechanical flat tappet cam there's no valvetrain adjustment needed, however you might want to take the valve covers off and look at the oil drains and for any sludge issues, which could be a telltale of what's going on inside the engine.

Where do you hear the "clacking" from? The top or the bottom of the engine? Does it sound like the same speed as the engine, or half speed when you give it gas?

Mark Houlahan
Brand Manager
Mustang Monthly Magazine

1965 FFR Roadster 427W/TKO-600 5-speed
1966 Mustang 289-4V/C4 Auto
1968 Mustang 4.6L Three-Valve/5R55S Auto
1990 Mustang 306/AOD
2002 Explorer Sport Trac 4.0L V-6/5R55 Auto
2005 F-150 4x2 4.2L V-6/4R70W Auto

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New User
Posts: 11
Joined: 05/11
Posted: 06/12/13 08:17 AM

Thanks for info Wayne & mark u guys are awesome!  Will start with the oil pressure tester. Thanks a again.  

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