429 oil pressure issue

Help Support 7173Mustangs.com:

afeng79

Well-known member
Joined
Apr 23, 2014
Messages
107
Reaction score
0
Location
Vandenberg AFB, CA
My Car
1972 Mustang Hardtop
Hey all, I got around to get the 429 TJ motor in my 72 running. Everything is hooked up and no visible leaks anywhere after running for about 3 minutes at idle with occasional revs. I get in the car to turn it off and notice the oil light on the instrument panel is lit up. I quickly shut off the engine and start to worry. To make sure the sending unit wiring wasn't haywire I unplugged it from the sending unit while running and sure enough as expected it turned off. So now I know its not the old wiring sending a bad signal. Do I really have low oil pressure and if so how low? Well I unscrewed the oil pressure sending unit at the back of the intake manifold, left it off completely, turned the car on and for about 3 seconds watched the volcano of oil shoot out from the sending unit hole, deflect off the hood and go EVERYWHERE.

Ok so, now I'm confused. Doesn't this mean I have pretty significant oil pressure for it to shoot out like that especially at the very farthest point away from the oil pump? Could this be a bad brand new sending unit or is there something else I'm not considering? Please help.

Next step is to hook up a oil pressure gauge there and see what I got. I'll post the results once I do. Also, I did replace the oil pump and pickup before running the engine.

 

turtle5353

VIP Members
Joined
May 15, 2011
Messages
3,420
Reaction score
248
Location
PA
My Car
1971 Mach 1 Mustang
Only way to know for sure is to hook up a mechanical gauge. Don't rely on the idiot light. You can pick up a cheap oil pressure gauge for testing for $20. I keep an old one in my tool box for just such an occasion.

 

Bill73Ragtop

Long time vintage mustang hobbyist
Joined
Apr 19, 2011
Messages
1,411
Reaction score
29
Location
Buffalo, NY
My Car
1969 Convertible Restomod enhanced.
former owner (25 yrs) of 1973 Convertible, 351c, A/C, RA
Keep in mind there are two oil pressure switches, one for warning light and one for gauges. Having the wrong one will give you issues.

As turtle5353 said, check with mech gauge before anything else.

 

afeng79

Well-known member
Joined
Apr 23, 2014
Messages
107
Reaction score
0
Location
Vandenberg AFB, CA
My Car
1972 Mustang Hardtop
Well I am anxious to get home after work and put a gauge to it. It's been bugging me all day. I think when I went to autozone for that new sending unit I opted for the one without gauges. But who knows. Anyways I think harbor freight has an oil pressure gauge for $24.99. What pressure should I be looking for? I've heard everywhere from 10 psi idle to 65 psi idle on these BBF engines!

 

barnett468

Well-known member
Joined
Nov 3, 2014
Messages
1,097
Reaction score
10
Location
us
My Car
i have a collection of mustangs
Well I am anxious to get home after work and put a gauge to it. It's been bugging me all day. I think when I went to autozone for that new sending unit I opted for the one without gauges. But who knows. Anyways I think harbor freight has an oil pressure gauge for $24.99. What pressure should I be looking for? I've heard everywhere from 10 psi idle to 65 psi idle on these BBF engines!
you can get an in car mounted gauge for $24.00 too.

the pressure at idle only needs to be around 5 psi but should be at least 20.

 

basstrix

VIP Members
Joined
Sep 3, 2015
Messages
555
Reaction score
10
Location
AZ
My Car
1972 Mach 1
1971 Ranchero
If you have a hydraulic cam, you'll hear a lot of valvetrain noise when o/p gets low.

You can go to home depot or the like and buy a cheap gage, you'll just need the correct fitting. They sell a gauge used for leak testing that's less than $10.

I'm guessing Bill is correct...you probably have the sender for a gage instead of the one for a light.

 

afeng79

Well-known member
Joined
Apr 23, 2014
Messages
107
Reaction score
0
Location
Vandenberg AFB, CA
My Car
1972 Mustang Hardtop
Yea I might opt for getting a gauge installed inside the car. I can't believe they didn't provide a gauge for something so important on the base non-Mach1 models. BTW, is it really only 5 psi minimum? That seems low but I've seen that number floating around other BBF forums. I've been told that pressure and flow are two totally different things and to not get them mixed up. You can have good flow but low pressure or bad flow with great pressure. Thanks for all the tips.

 

barnett468

Well-known member
Joined
Nov 3, 2014
Messages
1,097
Reaction score
10
Location
us
My Car
i have a collection of mustangs
BTW, is it really only 5 psi minimum? That seems low but I've seen that number floating around other BBF forums. I've been told that pressure and flow are two totally different things and to not get them mixed up. You can have good flow but low pressure or bad flow with great pressure. Thanks for all the tips.
If the idle and load is low enough, 3 psi is enough.

 

MeZapU

Well-known member
Joined
Feb 12, 2011
Messages
830
Reaction score
11
Location
Southery, UK
My Car
12 GT
73 Mach 1
85 GT
66 F-100
In this quick video you can see how the oil pressure is on my fresh 351c acts. I'm using a standard oil pump, 10w30 oil, and the gauge is hooked up to the rear of the block just as it would be on a 429/460. There is a bit of heat in the engine. You can see how the pressure builds on startup and how it bleeds down after shutoff. Temperature and oil viscosity will effect pressure at idle, as will bearing clearances with those things being equal.

Just something for your reference.

[video=youtube]

 
Last edited by a moderator:

MotoArts

Well-known member
Joined
May 30, 2011
Messages
935
Reaction score
6
Location
Pittsburgh, PA
My Car
'71 Sportsroof
'90 Mustang 7-Up 5.0 ragtop (sold after 20 years)
'66 Sunbeam Tiger Mk.IA
The factory oil pressure gauge in my 5.0 reads almost zero at hot idle, goes up to about 50 at cruise RPM.

Been that way for the past 40K miles and 15+ years when using 5W20 or 20W50, doesn't seem to matter.

Engine is stock original, spotless inside, has around 150K on the odo, and makes no funky noises. Tired and unimpressive to drive? Yes. Will I change bearings and pump just to improve pressure?

Nah.

 

rocket366

VIP Members
Joined
Jan 14, 2014
Messages
1,170
Reaction score
14
Location
Martinez, CA
My Car
73 Coupe 351c
Old rebuild of 351C by PO...

I get 15-20 hot idle to 40-60 2K-4K

with mechanical gauge tapped at back of block.

Paul

 

Hemikiller

VIP Members
Joined
Jul 12, 2010
Messages
3,321
Reaction score
512
Location
Killingworth, CT
My Car
71 Mach 1
65 coupe
Here's the gauge sender..

5971586_bwd_s334_pri_larg.jpg


...and the idiot light switch...

5971632_cbw_s367p_pri_larg.jpg


They don't play well when mixed up.

FWIW, the light should turn off with the wire disconnected from the switch. To test, ground the wire and the light should turn on.

 

afeng79

Well-known member
Joined
Apr 23, 2014
Messages
107
Reaction score
0
Location
Vandenberg AFB, CA
My Car
1972 Mustang Hardtop
Alright guys, I can confirm I purchased the GAUGE sender at autozone instead of the LIGHT sender! How do I know? Because they look vastly different and when I told the parts counter at Autozone what I needed I was thinking in terms of the 71 Thunderbird instrument cluster since that's what the motor came out of. For those of you with swap motors or swap items on the engine making your car a Frankenstang, I'm sure you can attest to the confusion when going to a parts store counter. Rookie move. Nevertheless, I ended up working very late all week and didn't have the chance to hook up the oil pressure gauge to see what I have. I'm sure it's nominal pressure but peace of mind is priceless. I'll update this thread with the oil pressures I have at various RPM ranges and see how it compares to what yall have seen on your engine.

 
Top