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Rich
08-11-2009, 10:40 AM
Ok, Heres the deal. Gen IV motor. Put my motor back together after rebuilding heads.
This time out, I wanted to get a good feeling about how motor was running, so I added some additional instrumentation. I installed fuel pressure, water pressure, and oil pressure, (all mechanical). Still need to install oil temp as well.
But now with mechanical oil press. I am seeing some things on the gage.
Great oil pressure at start, 80-90 cold. After warm up, drops to 60 or so while cruising about 3-4 K rpm's. But, also found out that if running harder at around 4500-5000rpm's, oil pressure started to slowly drop off. I watched it go down to 25-30psi or so, then I backed off. Down at idle, while hot, I watch pressure slowly rise from 20psi or so, back up to 40, in about 3 minutes. I was running straight 30 Rotella oil with pur. filter. I am wondering if I'm aerating my oil due to overfill. Originally, pan was steel 8 qt. Was rusted, so buddy gave me older merc aluminum pan, which has the cooling fins molded into it. I don't know much about this pan in there. Wondering if it's not an 8 qt capacity. I had put 8 quarts in, plus whatever residual was left in pan lines, etc... Does anyone know that pan, and its capacity? Plan is to change out oil today, and refill with Mobil 1, 15-50. This time will only put in 6 quarts, plus residual, and check it out again to see if it drops?
Any thing I am missing, or does this sound like correct diagnostic plan.
Thanks as always guys..
Rich

Ratickle
08-11-2009, 10:53 AM
Don't forget that you have a pan, cooler, oil lines, valley, etc that all have to have oil. My engines, on average, use three quarts more than the pan holds. Not all the same though.

Do you have an accurate dipstick?

Rich
08-11-2009, 11:05 AM
Dipstick is aftermarket junk. Tube is correct for pan, but not the stick. At least I don't trust it I guess. It will read between the lines presently with the six quarts in it.

Rich
08-11-2009, 11:30 AM
Ok, now even more befuddled. I believe I am looking at my same aluminum oil pan, in classified's on other site. Seller "believes" it might be a 10 quart.
Am I actually running low on oil? with only 8 quarts. And if so, did not think 2 quarts shy would cause pressure to drop off. What gives.

Trim'd Up
08-11-2009, 11:36 AM
The finned aluminum merc pans are 8 qt unless it has the "T" sump that came on the merc racing motors but they were made by GIL I think. I swear I posted to this once already.

Trim'd Up
08-11-2009, 11:38 AM
Dipstick is aftermarket junk. Tube is correct for pan, but not the stick. At least I don't trust it I guess. It will read between the lines presently with the six quarts in it.
Aftermarket dipsticks have to me marked yourself or cut from the handle end to match your pan.

DAREDEVIL
08-11-2009, 11:50 AM
Ok, now even more befuddled. I believe I am looking at my same aluminum oil pan, in classified's on other site. Seller "believes" it might be a 10 quart.
Am I actually running low on oil? with only 8 quarts. And if so, did not think 2 quarts shy would cause pressure to drop off. What gives.

I am pretty sure its a 10 quart pan.

But on another thing ,,,i would defenatley get rid of the mech. fuel press !!!

SOME TIMES IT GOES BOOM.:seeya:


The reason why the oilpress drops at WOT is because now the oil is all the way in the top end and almost nothing in the pan.
Add. 2 more quarts of oil and then mark the dipstick new as well.
Should be a little closer to stock.

Rich
08-11-2009, 11:58 AM
Ok, We have one vote for 8 quarts, one for 10 quarts.
Can 8 quarts of oil really end up everywhere but the pan causing pressure to drop?

BTW, I hear you on the mech fuel guage. It was installed temporarily so I could read while driving. Had a severe lean out condition, and with this rebuild, wanted to ensure I had proper fuel pressure.

ROGUE
08-11-2009, 12:04 PM
I had the same aluminum pans and got rid of them. I dont think they held as much oil as the stamped steel ones and had oil temp problems until I switched back to the steel 8 quart pans. Does yours look like this?

The stamped steel ones have more "pan" in the front and hold more oil.

DAREDEVIL
08-11-2009, 12:11 PM
I had the same aluminum pans and got rid of them. I dont think they held as much oil as the stamped steel ones and had oil temp problems until I switched back to the steel 8 quart pans. Does yours look like this?

The stamped steel ones have more "pan" in the front and hold more oil.

Ok,,,if its that pan u have then i would say 6-8 quarts.
I ment the aluminum with the kickout on both sides.

And i don't think it can happen that all 8 quarts are in the top end but atleast 2-3 @ WOT.

Filter holds 1/2 ,lines another including the coolers,,so thats 1.1/2 quarts not in the pan.

Rich
08-11-2009, 12:13 PM
I had the same aluminum pans and got rid of them. I dont think they held as much oil as the stamped steel ones and had oil temp problems until I switched back to the steel 8 quart pans. Does yours look like this?

The stamped steel ones have more "pan" in the front and hold more oil.

Same one !!
I will change out, but not at this point in the season...
Do you remember how much oil capacity???

ROGUE
08-11-2009, 12:23 PM
Im thinking it was 5. They used this pan in the inboard versions of the 7.4 if I remember right. 5 quarts in the pan + lines, cooler and filter. When I changed back to the stamped pans (1988 school bus pan from GM) (GM 14097240) my WOT oil temp dropped 30 degrees. Pickup for that pan is GM 14103147.

Rich
08-11-2009, 12:36 PM
Im thinking it was 5. They used this pan in the inboard versions of the 7.4 if I remember right. 5 quarts in the pan + lines, cooler and filter. When I changed back to the stamped pans (1988 school bus pan from GM) (GM 14097240) my WOT oil temp dropped 30 degrees. Pickup for that pan is GM 14103147.

Wow, big difference from 8 quarts if indeed 5 quart pan.
Now you got me thinking about that pickup tube as well. I am sure pickup is stock gm truck motor variety, since this block started life there. Hopefully it's in there deep enough, but if indeed this pan is only 5 or 6 quart, it should be?

I guess I will try out the 6 quart fill idea, plus whatever was left in system, and try that, paying close attention to my results. Hopefully I am looking at aeration issues, and not insufficient oil issue.

ROGUE
08-11-2009, 01:29 PM
Based on how you describe the pressure drop, it sounds like the oil is getting very hot (thin) which could be from overfill and aeration. Your plan sounds valid and yes, use at least a 40 wt oil or a multivis. I like the Shell Rotella 15W40 but the mobile 1 15W-50 is fine too. Get that oil temp gauge installed asap. If you are running out of oil, the pressure gauge would drop quick or bounce around more than just slowly dropping with load (and temp).

Ratickle
08-11-2009, 01:59 PM
Based on how you describe the pressure drop, it sounds like the oil is getting very hot (thin) which could be from overfill and aeration. Your plan sounds valid and yes, use at least a 40 wt oil or a multivis. I like the Shell Rotella 15W40 but the mobile 1 15W-50 is fine too. Get that oil temp gauge installed asap. If you are running out of oil, the pressure gauge would drop quick or bounce around more than just slowly dropping with load (and temp).

Good point.

I run 14 quart Gils. Take no chances........:)

ROGUE
08-11-2009, 02:14 PM
I also never liked the cold flow restriction through a tight filter so 2 in parallel is better than one. Wish I could have fit the bigger pans and coolers but my total oil is now over 11 quarts and holds 250 before the cooler at WOT.

MERPerformance
08-11-2009, 07:26 PM
Is your oil pan stamped steel, is it wide open or does it have a flat section of steel in it,
do you have a windage tray attached to the main bolts?

Rich
08-12-2009, 02:04 PM
Is your oil pan stamped steel, is it wide open or does it have a flat section of steel in it,
do you have a windage tray attached to the main bolts?

Oil pan is exactly like the one pictured in post 9.

I appreciate all the comments. I was able to go out yesterday for a while, but once my daughter and her friends got wind of me going out, they successfully turned my shakedown run into nothing more than an afternoon of tubing up and down the river and swinging off tarzan swings, which was ok by me. It was a beautiful day out. No chance to really open it up.. But I can say that for the hour or so of constant zig zags and turns at about 3k rpm's, oil pressure remained steady at 60psi. Whenever down at idle, pressure never dropped below 25psi or so. As somebody mentioned already, pressure drop off was slow and gradual, no spikes or anything like that.
I would like to add additional quart for margin and try again, but won't know for sure till I can wring it out for a good run. I definitely wish to install a oil temp sender. This will hopefully let me know greater detail of what is going on. I realize best is in the pan, but don't want to pull motor right now. Perhaps will tap into remote filter housing for now to get a baseline. I currently do not have gage for such, nor a place to put it right now. Can somebody recommend where and what to get which will suffice that is reasonable in price?

Ratickle
08-12-2009, 02:14 PM
Maybe I missed it. What size, and how old, is your oil cooler? It just may be oil temp which can be caused by a multitude of things.

Rich
08-12-2009, 02:43 PM
BTW, Here is pic. Old school Mark IV.

Rich
08-12-2009, 02:44 PM
Maybe I missed it. What size, and how old, is your oil cooler? It just may be oil temp which can be caused by a multitude of things.

Orig merc equipment..

PatriYacht
08-12-2009, 03:04 PM
It's either high oil temps or airation of the oil or both. Get that oil temp gauge on there as soon as you can and don't let the temp go above 280. The pan is at most 6 qts. If you have the room, Napa sells a 2 qt. filter made by Wix. Easy way to get another qt. of capacity. Merc recommends 40 wt. oil in most climates, don't use 30wt. unless you boat in freezing temps.

TomZ
08-12-2009, 04:39 PM
I'll second the 40 wt. comment. On my small block, Rotella 15W40 isn't cutting it at high rpm, so I'm going back to 20W50. I still hold a minimum of 50 PSI at extended WOT with the Rotella, but the 20W50 (Penzoil at the time) held over 60 PSI.

I hold about 10 quarts.

Tom

ROGUE
08-12-2009, 05:46 PM
My oil pressures never, ever, go below 60 due to my insanely critical bearing clearances and I run rotella 15-40. however, I use a 3" by 18" cooler and hold around 250 wot now. I would not just add a quart of oil until you have had a chance to do the wot test while watching the pressure gauge and hopefully while watching the temp. Unless of course you add the big filter as suggested by Patriyacht. You can drill and tap the top of the stock filter body for a sender or if you have the older ones there was an unused port you could use. SSComp has very nice inexpensive gauges ive used for years now.