TheSamba.com :: View topic - Engine runs for first time! (now, low oil pressure)

Tue Nov 17, 2009 3:28 pm

Today the long saga of my engine rebuild comes nearly to a close! Today I successfully started and ran the 20 minute breakin of my new "special camper" engine, with HAM heads and Raby valvetrain kit. Nothing sounds sweeter.

I ran into a few minor roadblocks, initially the engine would start and then die immediately. Or course I looked for the typical vacuum leaks but couldn't find any. Eventually I figured out the injectors were not firing, it was starting on the cold start valve alone. That led to a bunch of troubleshooting that ended up with the ECU plug not fully seated - duh!

During the break-in the engine did not run perfectly, some stumbling especially when giving it gas and it seemed to want to die below about 1400 RPM. I timed it quite roughly and it seemed to improve a bit, but I figure I still have some tuning/investigating to do. The important things, no oil leaks (except a valve cover gasket which I took care of), no exhaust leaks, good oil pressure, good compression. Whew!

Tue Nov 17, 2009 3:44 pm

Congratulations WT. I hope to be doing a cam break-in this May. Right now, that seems like a million years away, but in the meantime, there are a million other things to take care of. :shock:

I WILL CAMP IN THIS BUS THIS SUMMER!!! :lol:

Wed Nov 18, 2009 3:25 pm

Engine is running beautifully now... not sure what I did, honestly, other than screw the AFM idle mixture in a tad. It seemed to run better over time, intially like crap, then kinda OK but hesitating when given throttle, now just fine. Drove it around a bit, but not up to highway speeds. I don't know what the problem was, all I can think of is that maybe the injectors were a bit clogged from sitting 8 months.

Only real worrisome thing is idle oil pressure reads low... like 2-3 psi. It shoots right up when given gas, though, about 17 psi at 2000 rpm and 30 psi at 3000 rpm. This is with the oil at about 170 degrees.

I'm not going to panic, yet, though, I'm not real confident in the setup of my MGL engine monitor so the calibration may be off.

Wed Nov 18, 2009 6:25 pm

Hmmm... I've checked the calibration of the EMS-1 using a series of known resistors, and assuming a linear 10-180 ohm 0-80 psi sender, and it is a bit off, reading about 4 psi low So my 2-3 psi corresponds more to 6-7 psi. This is at about 800 rpm. Still low... I'll have to see how it does after a freeway run.

Of course I'm also assuming the sender is accurate. Wish I had a mechanical guage to verify.

Wed Nov 18, 2009 6:29 pm

Have you broken in the camshaft?

Can you score a mechanical OP gauge?

Wed Nov 18, 2009 6:44 pm

I did the camshaft break-in, 20 minutes at 2500 RPM give-or-take, using Joe Gibbs break-in oil.

Now that I think about it, I have a mechanical guage which I'm using for fuel pressure (mounted on the fuel rail) which I should be able to adapt to measure oil pressure using some fittings. I'll do that tomorrow...

Thu Nov 19, 2009 9:03 am

Long post, I apologize.

OK, this morning I realized that because I installed the dual-pole oil pressure sender through the tin instead of relocating it, it is a non-trivial task to remove it without either damaging it or removing a bunch of stuff that's in the way to get access with a pair of vice grips. Or both.

So, instead I did a little more troubleshooting. I had run two grounds from the engine monitor, one to the frame ground in front, and one to the engine block in back. I then re-read the directions which said run just one to the engine block, so I removed the ground at the front.

I also had not bothered to hook up the oil idiot light. So I did that.

Then I just started the engine from cold and observed. The oil pressure indication initially shot up to around 72-75 psi. I suppose that's to be expected. Driving around town, with the engine still relatively cold, the pressure stayed around 60 psi and then started dropping slowly once the oil temp hit about 120.

I took it on the freeway and the oil temp crept up, but seemed to level at around 150. Outside temp around 50. Cylinder head temps around 330 (!!), oil pressure at around 40psi (doing 60mph). Drove this way for 20 minutes or so, everything seemed stable, engine doing fine, powerful.

On the way back, I hit stop and go traffic. Oil temp crept up to around 175. At a dead stop, with the transmission in drive (I have an automatic), RPM's around 775, the oil light would come on and pressure would indicate 4 psi. Goose the gas just a tad, RPM's up to around 900, oil light goes out and oil pressure indicates 5 psi. At 1000 RPM indicating around 8 psi, 2000 rpm 20 psi.

Hmmm.

So, when I get home (engine still hot), I hooked an ohmmeter directly onto the pressure sender. With the engine off, the sender reads 5.4 ohms. With the engine running, in drive (wheels chocked of course!), the sender reads 15.7 ohms. Oil light on. In neutral, oil light off, sender reads 19.1 ohms.

Supposedly, the light comes on at around 11 psi using this sender. Supposedly, also the sender is 10-180 ohms with 10 ohms corresponding to 0 psi and 180 ohms corresponding to 80 psi. Obviously it's not very precise. Nevertheless, I believe it's telling me the truth that my oil pressure is marginal at idle. Not what you want to see on a brand new rebuild. However the running pressure seems OK. I think I'm going to chalk this up to "don't watch the gauges, just drive the damn thing". I sure don't feel like ripping the engine out again.

FYI I'm using a Type I Shadek pump, and I've switched to 20w50 oil after the initial breakin.

Thu Nov 19, 2009 9:31 am

I'm not sure if it's different for an automatic, but I think you should be idling a bit higher, like 900 +/- 50. This will get your oil pressure up. It's a rule of thumb I read that one should get 10psi per 1000 rpms. It seems you're getting that in the upper range but just not making it at idle.

Another thing to consider is the accuracy of your tach. My vdo disagrees with my snap-on timing light by about 100rpm - you may be idling lower than it says you are, like 650.

The idiot light is supposed to come on at, I think 7psi stock. The vdo double pole sender I've read and seen will make it come on at maybe 9ish.

Seems like pretty high pressure at startup. 20w50 I've always thought was more for summer; 10w40 I think would be better for 50 degrees.

Thu Nov 19, 2009 9:49 am

Sometimes the VDO Di-pole sender needs to be grounded to get more correct results (they tend to read a bit low). I would confirm them with the mechanical gauge T'ed into the di-pole sender to see just how they compare.

Nothing wrong with the oil temps though. 180-220º is the range you are looking for.

Oil may be a bit thick for a new engine though.

Thu Nov 19, 2009 10:02 am

I threw the thick oil in there after being scared by the low oil pressure readings. Initial cam-break in oil was 5w30. I'll run this for 100 miles then swap with 10w40... see what that does.

I am surprised the oil temp is so low on the freeway. I haven't seen 180 yet, even stop and go. I'm using an MGL avionics precision sender mounted in a "Whip618" aluminum plate (I think you have the same one Randy). It reads dead-nuts accurate outside air temp when engine is cold.

I'll see if I can get the sender off without breaking anything. I did use a dab of sealant on the threads, which I also now realize I shouldn't have done. However it does seem to be grounded.

Thu Nov 19, 2009 10:45 am

How is the idle oil pressure in Park or Neutral?

The automatic transmission equipped bus should have an ajdustment to increase idle speed when in Drive.

If your concern is only when idling in Drive, then you may be idling too slowly to build the necessary pressure.

Thu Nov 19, 2009 12:10 pm

we used royal purple break in oil. It is 30 wt and we found that at idle the VDO gauge would trip the low oil light even though we had 10 pounds at 900 RPM. We stepped up to 20/50 and the issue went away. My 1971 1600DP T1 motor used to act the same. VDO has their idiot light set just a tad high but that warning is better than a "sorry we were late telling you that your oil pressure dropped" warning.

Thu Nov 19, 2009 2:17 pm

I swapped the VDO sender with the stock switch and drove around looking for fittings. The light never came on.

Never found the proper metric fittings so I made do with a 1/8NPT grease gun hose. I wasn't sure about messing up the case so I screwed it in very gentle-like, pretty much just past hand tight. As I expected it leaked a bit but not enough to throw off the readings, I don't think.

Anyway, using a laboratory grade McDaniels stainless steel pressure gauge, and the tachometer off my dwell meter, I get the following (at oil temp 170):

800 RPM 5.5 psi
1000 RPM 8.0 psi
2000 RPM 23 psi
2500 RPM 34 psi

I didn't rev it higher out of respect for the neighbors and the growing puddle of oil under the bus.

Eh, I'm not happy with it. I'm not going to pull the motor either. It passes the Bentley spec. I'm going to order the fittings I need to relocate and tee the sender, and run both the stock switch and the VDO sender. Then I'm going to calibrate the EMS-1 (it does have a user-defined calibration feature) so that the readings match the mechanical guage.

Then I'll just watch and make sure it doesn't get worse.

Thu Nov 19, 2009 2:32 pm

That is really not that bad.

Rule of thumb is that it should have 10 psi at idle + 10 psi per 1000 RPMs, although I am not aware that number is published anywhere.

That may be a common thing when we run modified type 1 pumps, they deliver a fair amount of volume, but not pressure although I will defer to someone else who knows more about that.

What did you use for gasketing on the oil pump cover?

Thu Nov 19, 2009 2:44 pm

Randy in Maine wrote:
What did you use for gasketing on the oil pump cover?

I don't know... machine shop installed the oil pump and modified it to fit. I will find out.

Thu Nov 19, 2009 4:37 pm

I'd PM Jake and ask him to be sure, but it doesn't sound like you have a problem to me.

The owners' manuals for these Buses used to state that a flickering oil light at idle after a long highway pull was "normal", and I think the light flickered at about 5 or 6 PSI, but I don't recall exactly. As long as the light went out on acceleration you were OK.

Be certain you're using an oil filter with a check valve, of course.

Thu Nov 19, 2009 7:18 pm

I've been doing a lot of reading on this forum, and I'm thinking I might want to investigate the oil pressure relieve valve.

I saw 72-73 psi at startup, cold However when I put a 180 ohm resistor on the gauge it reads 73 psi... so that means that I was full scale of the sender. Could have been even more pressure than that.

Yet my idle pressure is low.

Stuck oil pressure relief valve?

Fri Nov 20, 2009 12:57 pm

Whirl,

Here are my oil pressure numbers to compare:

New rebuild 2.0 FI
automatic
MGL avionics E1 verified with mech gauge and tach
no oil temp, haven't installed taco plate yet
10W30 break-in oil
engine warm, run about 45 minutes
Cyl Head temp 310 F

800 rpm (Drive) 13 psi
1000 (Park) 15
1500 32
2000 45
2500 48

I get 60 psi on cold start. I have a late case with only one oil pressure relief valve. Is is possible you have a problem with your oil pressue relief valve(s) ?

Fri Nov 20, 2009 1:30 pm

Hi WT, I built a similar engine with Raby 9550 cam kit. I have the same OP as you but Im not worried about it. My light comes on below 1000 RPM, but I idle at around 1300 RPM. Whats your idle? I installed my VDO sender on the end of a brake hose and a Y on the cooler with the light P switch. After break in, I switched to 20/50 Amsoil Syn. with high Zinc .
Im running a stock Tp4 pump with high mileage but good tolerances.
Can't say enough good about the Raby 9550. After 500 miles, I still haven't had any noticeable valve adj. necessary. Not even after break in. How about you?

Fri Nov 20, 2009 3:02 pm

GusC2it wrote: Hi WT, I built a similar engine with Raby 9550 cam kit. I have the same OP as you but Im not worried about it. My light comes on below 1000 RPM, but I idle at around 1300 RPM. Whats your idle? I installed my VDO sender on the end of a brake hose and a Y on the cooler with the light P switch. After break in, I switched to 20/50 Amsoil Syn. with high Zinc .
Im running a stock Tp4 pump with high mileage but good tolerances.
Can't say enough good about the Raby 9550. After 500 miles, I still haven't had any noticeable valve adj. necessary. Not even after break in. How about you?

My idle when fully warm is around 800 in drive, 950 in neutral. When the engine is cold it's kind of all over the place, 1200-1300 in neutral and still dropping to 800-850 in drive. I guess the cold transmission fluid puts more load on the torque converter.

I checked the valve clearance after cam break-in and it was dead on, "loose zero".

My case is single relief. I'll check it when I drain this oil. In the meantime I'm going to quit worrying so much and enjoy my new motor.