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Old 06-22-2010, 02:03 PM
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Melling oil pump issue

I just fired up my rebuilt SBC 400. .030 over bore, flat top pistons stock rods / crank. mild cam. It ran good, but with about 45 minutes on the engine, a oil pressure issue developed. After starting the engine I had 55-60 psi at idle, now at idle (900 RPM) the gauge reads zero, Off idle it is 35 psi but when reving the engine the pressure needle flutters rapidly. This is a mechanical guage. I drained and inspected the oil, It is very clean and no sign of metal particulate in the filter. I thought it might be the guage, replaced the guage and it does the same thing. I am using shell Rotella T 15-40 wt oil and a melling m55 pump. Engine runs quiet and good with good oil at the rocker arms. Any Ideas?

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Old 06-22-2010, 02:13 PM
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What are you using for an oil filter?
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Old 06-22-2010, 02:16 PM
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Oil pressure issue

Supertech ST-5 oil filter.
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Old 06-22-2010, 02:47 PM
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Quote:
Originally Posted by Studebaker
I just fired up my rebuilt SBC 400. .030 over bore, flat top pistons stock rods / crank. mild cam. It ran good, but with about 45 minutes on the engine, a oil pressure issue developed. After starting the engine I had 55-60 psi at idle, now at idle (900 RPM) the gauge reads zero, Off idle it is 35 psi but when reving the engine the pressure needle flutters rapidly. This is a mechanical guage. I drained and inspected the oil, It is very clean and no sign of metal particulate in the filter. I thought it might be the guage, replaced the guage and it does the same thing. I am using shell Rotella T 15-40 wt oil and a melling m55 pump. Engine runs quiet and good with good oil at the rocker arms. Any Ideas?
Sounds mostly like a gauge issue. Not that you shouldn't be concerned, but I'd start with the gauge system. The one thing it could be if it is the pump would be the relief valve is stuck in a partially open position and is chattering as the pressure comes up or the inlet is leaking air. But first I'd verify the gauge and the lines to it as this takes a lot less engine disassembly.

Bogie
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Old 06-22-2010, 03:34 PM
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Sounds like oil filter relief valve very common with Fram and other cheaper filters,Wally World and Autozone have AC-Delco get one or a NAPA Gold.
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Old 06-22-2010, 04:08 PM
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I have seen the mixture of oils, assembly lubes and certain filter media result in a plugged filter. I only race Fram HP4 and have never had a filter problem.
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Old 06-22-2010, 04:14 PM
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Quote:
Originally Posted by Studebaker
I just fired up my rebuilt SBC 400. .030 over bore, flat top pistons stock rods / crank. mild cam. It ran good, but with about 45 minutes on the engine, a oil pressure issue developed. After starting the engine I had 55-60 psi at idle, now at idle (900 RPM) the gauge reads zero, Off idle it is 35 psi but when reving the engine the pressure needle flutters rapidly. This is a mechanical guage. I drained and inspected the oil, It is very clean and no sign of metal particulate in the filter. I thought it might be the guage, replaced the guage and it does the same thing. I am using shell Rotella T 15-40 wt oil and a melling m55 pump. Engine runs quiet and good with good oil at the rocker arms. Any Ideas?
Will the gage show only 35psi hot even with the engine running at 3-4000 RPM? If so, and the needle is rapidly fluctuating (very rapidly), this is a relief valve or spring problem, IMO.

You also have a pressure relief located under the filter, in the filter mount assembly. Check to be sure the spring is OK and the fiber disc is seating as it should. I always remove this relief valve and plug the hole...
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Old 06-23-2010, 01:32 PM
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Oil pressure problem

Thanks for the input, I will replace the filter and plug the filter mount bypass valve and see if that cures it.
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Old 06-23-2010, 03:14 PM
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Quote:
Originally Posted by cobalt327
Check to be sure the spring is OK and the fiber disc is seating as it should. I always remove this relief valve and plug the hole...
Me too keeping in mind that the filter must then have a bypass built-in or else a blocked filter can cause no oil flow , I think most filters nowadays do have this bypass in them yes/no?
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Old 06-25-2010, 06:02 AM
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Fixed it!

Thanks for your advice, I changed the filter to a Fram PH-30 and no more issues. I'm just glad it was that simple! Now I have a spare oil pressure guage for another project since I bought another one thinking it was the guage. Engine runs wicked strong, it's got better throttle response than my wife at a shoe sale.
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Old 06-25-2010, 08:08 AM
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Quote:
Originally Posted by Custom10
Me too keeping in mind that the filter must then have a bypass built-in or else a blocked filter can cause no oil flow , I think most filters nowadays do have this bypass in them yes/no?
I don't know of any filters that have bypasses built in them-you're thinking of anti-drainback valves. On a sbc, plug the bypass above the filter and when filter is plugged, oil pressure goes down and then you collapse filter media inside filter-so this requires keeping a close eye on your oil pressure.
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Old 06-25-2010, 08:52 AM
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Quote:
Originally Posted by Adam65
I don't know of any filters that have bypasses built in them-you're thinking of anti-drainback valves. On a sbc, plug the bypass above the filter and when filter is plugged, oil pressure goes down and then you collapse filter media inside filter-so this requires keeping a close eye on your oil pressure.
They are two different things, yes most filters have the anti drain back but also there are some such as WIX which have the bypass, this is from there web site and describes what I am referring too

"By-pass Valve Assembly -- spring loaded valve assembly that allows oil to by-pass the element under high-differential pressure conditions such as cold oil and/or excessively contaminated media. This allows lubrication of the engine, but without full-flow filtration."
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Old 06-25-2010, 09:01 AM
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While it is true that blocking the filter mount-located bypass will cause a reduction in oil pressure as the filter becomes more and more filled w/debris, the MAIN thing you want to be careful of, is jazzing the throttle when first starting a cold engine. This can cause the filter to balloon, and even burst, or cause the gasket between the filter and filter mount to blow out.

So if you plug the bypass in the filter mount- don't rev the engine cold. Something that shouldn't be done, anyway. This also puts more load on the distributor and cam gears and the pump/pump drive, but only to the point to where the oil pump's bypass is set to relieve pressure. As long as the pump's pressure relief spring isn't set too high, there won't be a problem.
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Old 06-25-2010, 09:32 AM
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Quote:
Originally Posted by Custom10
They are two different things, yes most filters have the anti drain back but also there are some such as WIX which have the bypass, this is from there web site and describes what I am referring too

"By-pass Valve Assembly -- spring loaded valve assembly that allows oil to by-pass the element under high-differential pressure conditions such as cold oil and/or excessively contaminated media. This allows lubrication of the engine, but without full-flow filtration."
I guess I stand corrected-thanks!
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Old 07-11-2010, 10:42 AM
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Problem came back

Well, thought I had the problem fixed but evidently not. Oil pressure is all over the place. sometimes it is fine, then on next start up it's 10 psi. I started researching Mellings new pump design changes and evidently others are have simular problems with the new m55 pump. I am not going to risk an engine failure because of this. I will pull the pan and replace the pump, I hear Milodon makes a good pump. For $30.00 I won't risk it. Why the design change from Melling, To save weight on the pump assembly, ***? I have checked two other engine kits that I have on the shelf and they also have the new design Melling pump. I will give these to my local machine shop. A thinner support on a OIL pump! I have been using melling pumps for over 35 years, NEVER AGAIN, WHAT ARE THEY THINKING! Just ordered a Milodon pump.

Last edited by Studebaker; 07-11-2010 at 12:11 PM.
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