Engines first start, not happy with oil pressure

JohnM · #1 (**permalink**) 03-30-2002, 04:28 PM

Hello All,

Well...after all these months of work I fired the engine today! A very satisfying sound. I was about 20 minutes into the 30 minute cam break in.... at that point of course a small water "jet" was shooting out of the side of the thermostat housing...but no oil or gas leaks. I of course had my eyes glued to the oil pressure guage. At first start up the oil pressure was at 60lbs. After the engine was hot and running at about 2200 for the break in my pressure slowly lowered..(scary to watch) to about 37lbs and held there. I am running 10w-30 weight oil, and my engine machinists like to lean toward the loose side in tolerences. The engine is a 351W 60 over with the typical Melling high volume pump. I shut down to work the water leak and think about the oil pressure. Friends say to change the oil to 20w 50 and my oil pressure should be back up to were I would like it.

Any thoughts and suggestions would be most appreciated.

Happy Easter to all

Thanks

John

dlowe01 · #2 (**permalink**) 03-30-2002, 04:56 PM

John, I am running about the same setup and my oil pressure with 10W-40 is now around the 60 mark. When I first started it up it was only around 45-50. I was using dual Fram filters and after reading some bad things about them changed them out to some Bausch filters. I could not beleive that the filters made that much difference. You might have a cloged or bad oil filter that is keeping your presure down. Just a thought since it was at about 60 and went down that much!

750hp · #3 (**permalink**) 03-31-2002, 05:23 AM

John, as a reference point I started my 351 stroker for the first time on Friday. It's also a loose clearance motor with a Melling HiVo pump. I used Castrol GP50 20W50 oil. I primed the oil system with a power drill attachment on the oil pump drive. Just with an old drill, the oil pressure went to 75psi. We then refitted the distributor and when the motor fired up, the pressure went straight to 80psi and came back to 70psi when warm and 75psi with a blip of the throttle.

I ran it for 15 minutes, then replaced the oil filter and took an oil sample to have it analyzed just to make sure everything's OK. I fitted a cheper brand of filter and refired the motor, and the oil pressures were identical to the previous filter.

If you don't have access to a local oil analysis firm, I'd recommend replacing your oil filter and cutting open your original one to make sure that there are no horrible speckly bits lurking in there. If it only costs you a few bucks for the peace of mind, I'd say it was worth it!!!

Good luck,

Hotfingrs · #4 (**permalink**) 03-31-2002, 05:35 AM

Try changing the filter, and see what happens. No matter how clean you THINK you have an engine, there is always junk left in the passages. You should never start a new or rebuilt engine without a protective screen that goes on top of the oil filter, made especially for this. After you do your break in you pull the filter off and take out the screen. The screen will be plugged with all the junk left in the passages. Then change the filter and oil.

JohnM · #5 (**permalink**) 03-31-2002, 06:31 AM

Thanks all,

I am going to change the filter and oil. I will install 20w50 oil. I have been searching some old threads on oil pressure. My general sense is that my pressure at 37 at 2200 or 2300 rpm is not that bad. I was hoping for more!! People throw around this 10lbs per 1000rpm ratio. My pressure dropped to the 37 after the engine temp came up so that 10w30 oil I have in there was to thin. My question is...do I need to worry is 37 adequate for a street car. I do not yet know what pressure I will have at idle...Every new step opens up many more questions. Let hope the oil change solves all these questions.

Thanks, will keep you informed

John

Tom T. · #6 (**permalink**) 03-31-2002, 08:47 AM

I think 37 psi at hot idle should be adequate. However, some of these guys seem to be running a similar set-up to yours with higher oil pressure, so what the heck, what they're suggesting makes sense, especially about getting out any crap that may be clogging up the works.

TT

Mr.Fixit · #7 (**permalink**) 05-03-2002, 04:53 PM

20-50 oil or 30 weight. Change the oil filter the first day after fire up. Don't worry 45 psi is plenty of pressure at rpm reguardless of what other people tell you.

webebob · #8 (**permalink**) 05-03-2002, 06:42 PM

How hot was your oil temps after 30 mins at 2200rpm? REAL hot I would guess. This is the hottest your oil will probably ever get. That also means the thinnest and lowest pressure you will ever see. Drop in the 50w and under normal driving conditions, I bet you will be pleased.
Besides that, if 37psi was your worst pressure, this would never cause a problem for a street engine. This would be too low for track work though.
2 cents worth.
Bob

Bob Parmenter · #9 (**permalink**) 05-03-2002, 08:11 PM

Hey John,

How about a little lubrication basics here. Although the world seems to think oil pressure is king, what lubricates your engine is oil FLOW. Pressure is the measure of RESISTANCE to flow. Before the flaming begins, oil pressure serves a purpose; as a measuring tool. Since all oils thin as they warm, and thinner oil has less resistance to flow, it is natural for oil pressure to drop as operating temperatures increase. You mentioned that the oil pressure gradually decreased. Since that is a normal condition, the pressure readings you were getting indicated normal behavior. Had you had either a sudden drop, OR a sudden significant increase (assuming no increase in engine speed, which would increase volume, which would show more pressure because the oil passages are a fixed size and increased volume means more resistance to flow) then the pressure CHANGE would be a valid indicator of a problem. Sudden drop indicates a lack of oil flow to measure, increase could indicate a restriction that could be blocking, or at best, restricting full flow. The variable there is where the obstruction is in relation to where the pressure sensor is. I'm not sure what the relavance of the oil filter comments are other than most oil filters have a relief, or bypass, valve. The purpose of that valve is to allow the oil flow to bypass a plugged filter (the filter engineers understand the principles, it's better to have dirty oil flowing than no oil flowing). While the advice to change the break-in filter is valid, due to the "assembly trash" it has collected not being left available for re-contamination, it very likely had nothing to do with the pressure changes you saw.

The numbers you observed would not be unusual for a 10w30, and yes, going to a 20w50 would give you higher pressure readings than the 10w30, but not as good of flow and very likely not as good of protection under the conditions you described. This is the good ol' USofA and "more is better" is a mantra for some, but at initial start up it should be more FLOW is better, not pressure. While inital start up is a stressful time for you, the engine is operating in a no load, relatively constant (assuming a gradual increase in RPM to the break in speed) speed condition. If no errors in assembly have occured that would cause a failure, and the cooling system is functioning, you should be fine.

Enjoy

Dominik · #10 (**permalink**) 05-04-2002, 01:02 AM

I can only speak for the Chevy at this stage.
We were used to installing either a 40 psi or a 55 psi by-pass spring in the pump, meaning that you won't have higher pressure readings than this when hot.
At 300 rpm, or so, not at idle.

Make sure you replace the oil filter after the first warm-up. The lubrication grease from lifters and cam gets stuck in the filter up to the point of no pressure left if the filter is clogged and you have no by-pass at the filter.

That is why I like the FRAM HP4 having a by-pass. The one in the block was blocked.

good luck,

Dominik

Dominik · #11 (**permalink**) 05-04-2002, 01:03 AM

that is 3000 rpm not 300 ...

JohnM · #12 (**permalink**) 05-04-2002, 03:09 PM

Time for an update,

Thanks all for your help and info. I have since changed the oil several times. I did put in 20 50 and had higher oil presuure. My engine machinist told me to use 10 40 and to get rid of the electrical oil presure guage and install a full face mechanical, which I did. My engine is a happy camper...starts right up...and sounds quite nasty. No leaks...idles at 1000 rpm for as long as I want.....all in all a good engine. I have since stopped worring what the oil pressure guage reads as number ....just that it reads oil pressure far above "0" With the electrical guage, which was a 1/2 face unit. it was not responding fast enough, I could not see the small increments of the oil pressure go up when I reved the engine. Now with the full face mechanical, it is easy to see that it changes when reved.

Thanks all for you insights and advice. I now move onto the instalation of the body.

John

Mr.Fixit · #13 (**permalink**) 05-06-2002, 02:30 PM

I highly suggest running a -3 (or even -4) braided stainless line with full radius elbows to the oil pressure gauge instead of the little nylon one that probubly came with the gauge. This will let you see the needly fluctuate if the oil pressure is, and notify you of the impending lubrication problem. The little nylon line that comes with most pressure gauges effectively dampen the pressure fluctuations, just watch how long it takes to react to fire up, shut down, or jazzing the throttle. The oil gauge should react quicker than the tach to a tap of the throttle at a stoplight. But anything beats an electric oil pressure gauge. You do have an oil temp gauge too, right?

Ken Oikawa · #14 (**permalink**) 05-07-2002, 05:16 AM

I use a 3/16 copper tubing to oil pressure gauge.

DaveR · #15 (**permalink**) 05-08-2002, 05:02 PM

This is unrelated to your pressure issues, but I'm also building a 351W, and I was wondering what cam profile you chose.

JohnM · #16 (**permalink**) 05-08-2002, 07:41 PM

Hello DaveR,

I don't have my cam card in front of me but from memory, Its a Comp cam hydraulic cam..lift in the 528 range with duration in the 280 290 range. Engine starts great, idles at 1000rm...but will probably be happier at 1100 to 1200 when I'm driving it on the street. Sounds quite nice. The engine recipe is as follows

69 351W block 60 over with windage tray
Keith Black pistons compression about 10:1 (block has been decked)
Weiand Stealth Intake
cast iron heads by Power Heads
Holley Street Avenger 670cfm
MSD Distributor and ignition
Horse Power ??? 375-400 should be more than enough.

E-mail if you have any questions

Regards

John