I tried this query with dragster.com but couldnt find anything similar in their hard to use search engine. Maybe someone here can assist.
My problem, if it is one, is that my 308/383 stroker motor is making around 40psi oil presssure cold on idle and about 10-20 psi hot on idle. This climbs to 100psi (the limit of the new VDO gauge) very quickly and I am unable to push past about 1/4 throttle (2000rpm) as I am concerned about possible damage. The build of this engine has been a nightmare of oil leaks, popped welsh plugs, broken oil pump gear teeth (which resulted in the 3rd rebuild in 18 months) and other dramas so you could understand my hesitation. I use 20w50. Was using 60w racing oil previously and had very low pressure.
Question is: how much pressure should I have? Do I need to limit the pressure somehow at big revs (6500rpm)?
My builder has assured me this is OK but hasnt provided much of an explaination. I realise my technical knowledge is lacking and thats why I'm asking the questions. Even if someone could refer me to a free site that explains these things I would be grateful.
Coops
Oil Pressure problems.
Moderator: DLRA
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Kevin Johnson
- Posts: 4
- Joined: Sun Jun 26, 2005 6:13 pm
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Possibly a bad relief valve?
Hi Coops,
I hope you have been able to sort this out in the meantime but if not here are some thoughts:
I am not personally familiar with the 308 but presumably it has an oil pressure relief valve and it sounds like it is not functioning properly. An old rule of thumb is 10lbs of oil pressure for every 1000 rpms. Some racers use somewhat less safely but it is a good rough start.
Usually oil pump relief valves have some sort of steel ball held in place by a spring. Often people will use washers, etc. to increase the amount of pre-load on the spring and thereby increase the amount of pressure. Another spring entirely may be present or perhaps is absent totally (?). This sort of mod may have been done by a previous owner (?). It could also simply be that there is debris clogging the valve somehow.
Kind regards,
Kevin
I hope you have been able to sort this out in the meantime but if not here are some thoughts:
I am not personally familiar with the 308 but presumably it has an oil pressure relief valve and it sounds like it is not functioning properly. An old rule of thumb is 10lbs of oil pressure for every 1000 rpms. Some racers use somewhat less safely but it is a good rough start.
Usually oil pump relief valves have some sort of steel ball held in place by a spring. Often people will use washers, etc. to increase the amount of pre-load on the spring and thereby increase the amount of pressure. Another spring entirely may be present or perhaps is absent totally (?). This sort of mod may have been done by a previous owner (?). It could also simply be that there is debris clogging the valve somehow.
Kind regards,
Kevin
Thanks for the reply Kevin.
I've only just pulled the pressure relief valve out on the weekend and checked it for binding and foriegn materials. There were some scuff marks near the top of the piston that I cleaned up but nothing that should have caused it to fail or jam shut. After I replaced the spring and piston I failed to get any oil pressure at all. A mechanic mate tells me that holden oil pumps are well known for being difficult to prime. He suggested removing the pump and packing it with vasaline to make it prime. If anyone has a simpler method I'd love to hear it as the wife wants her carport space back.
By the way, what pressure reading should I be getting from cold start with 20 W 50 oil?
Regards
Coops
I've only just pulled the pressure relief valve out on the weekend and checked it for binding and foriegn materials. There were some scuff marks near the top of the piston that I cleaned up but nothing that should have caused it to fail or jam shut. After I replaced the spring and piston I failed to get any oil pressure at all. A mechanic mate tells me that holden oil pumps are well known for being difficult to prime. He suggested removing the pump and packing it with vasaline to make it prime. If anyone has a simpler method I'd love to hear it as the wife wants her carport space back.
By the way, what pressure reading should I be getting from cold start with 20 W 50 oil?
Regards
Coops
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Kevin Johnson
- Posts: 4
- Joined: Sun Jun 26, 2005 6:13 pm
- Contact:
Are you doubly sure that you did not somehow leave the oil pickup tube out of the engine or did not tighten it to the block with a known good gasket? That could explain the lack of oil pressure too.
The idea re vaseline is good if the above is assured. On some engines you can remove the distributor and use an electric drill to independently prime the pump. On some of my old engines I had to take a spare distributor drive gear and grind off all the teeth meshing it to the cam -- but if this is not a straight forward task on the Holden for you don't do it as you don't need to add timing problems.
I would not be surprised to see 40-50 lb of pressure on cold startup at idle until the oil warms. A lot depends on how much clearance is present in your bearings (less clearance or new bearings = more pressure at idle).
Kevin
The idea re vaseline is good if the above is assured. On some engines you can remove the distributor and use an electric drill to independently prime the pump. On some of my old engines I had to take a spare distributor drive gear and grind off all the teeth meshing it to the cam -- but if this is not a straight forward task on the Holden for you don't do it as you don't need to add timing problems.
I would not be surprised to see 40-50 lb of pressure on cold startup at idle until the oil warms. A lot depends on how much clearance is present in your bearings (less clearance or new bearings = more pressure at idle).
Kevin
Coops wrote:Thanks for the reply Kevin.
I've only just pulled the pressure relief valve out on the weekend and checked it for binding and foriegn materials. There were some scuff marks near the top of the piston that I cleaned up but nothing that should have caused it to fail or jam shut. After I replaced the spring and piston I failed to get any oil pressure at all. A mechanic mate tells me that holden oil pumps are well known for being difficult to prime. He suggested removing the pump and packing it with vasaline to make it prime. If anyone has a simpler method I'd love to hear it as the wife wants her carport space back.
By the way, what pressure reading should I be getting from cold start with 20 W 50 oil?
Regards
Coops
Thanks for the suggestion but I cant really fill the oil filter as it is fitted sideways. Also I dont think the pick up is the problem as I had oil pressure previous to taking out the pressure relief valve, although its something I'll keep in mind to check on next time I build an engine. I'll yank the pump off tomorrow and try the vas suggestion. I'll take out the plugs and turn it over on the starter until I get pressure then try it out.
Would it be advisable to put a shot of oil in each cylinder to lubricate or am I just going to carbon up my plugs doing this?
Would it be advisable to change my oil immediately after putting vas in it or is it ok to run for a while?
Regards
Coops
Would it be advisable to put a shot of oil in each cylinder to lubricate or am I just going to carbon up my plugs doing this?
Would it be advisable to change my oil immediately after putting vas in it or is it ok to run for a while?
Regards
Coops
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Kevin Johnson
- Posts: 4
- Joined: Sun Jun 26, 2005 6:13 pm
- Contact:
Vaseline is white petrolatum and completely miscible with hot motor oil so the small amount used should be safe.
It sounds like the oil pump on the 308 is external. Most of the engines I tear down have internal ones that require removing the pan and then the pickup tube. There was a recent post on one of the Dodge forums about someone buying and installing a "good" short block with installed pan and then having no oil pressure -- missing pickup tube. I always try to remember to mention this in the installation instructions I provide. A lot of pumps have a slip-in driveshaft of some sort going to the block as well. It is very easy to forget this as when the pump is reinstalled everything looks ok.
The filter media in a typical oil filter will absorb quite a bit of oil before starting to pour out even if installed sideways. Slowly fill and spin it at an angle while doing so. When you see that the filter isn't soaking it up anymore just stop there.
A (small -- ~1tsp) shot of oil won't hurt -- this is a commonly done with compression checks with no ill effects especially if the plugs are out.
It sounds like the oil pump on the 308 is external. Most of the engines I tear down have internal ones that require removing the pan and then the pickup tube. There was a recent post on one of the Dodge forums about someone buying and installing a "good" short block with installed pan and then having no oil pressure -- missing pickup tube. I always try to remember to mention this in the installation instructions I provide. A lot of pumps have a slip-in driveshaft of some sort going to the block as well. It is very easy to forget this as when the pump is reinstalled everything looks ok.
The filter media in a typical oil filter will absorb quite a bit of oil before starting to pour out even if installed sideways. Slowly fill and spin it at an angle while doing so. When you see that the filter isn't soaking it up anymore just stop there.
A (small -- ~1tsp) shot of oil won't hurt -- this is a commonly done with compression checks with no ill effects especially if the plugs are out.
Coops wrote:Thanks for the suggestion but I cant really fill the oil filter as it is fitted sideways. Also I dont think the pick up is the problem as I had oil pressure previous to taking out the pressure relief valve, although its something I'll keep in mind to check on next time I build an engine. I'll yank the pump off tomorrow and try the vas suggestion. I'll take out the plugs and turn it over on the starter until I get pressure then try it out.
Would it be advisable to put a shot of oil in each cylinder to lubricate or am I just going to carbon up my plugs doing this?
Would it be advisable to change my oil immediately after putting vas in it or is it ok to run for a while?
Regards
Coops
Kevin
Thanks for the instructions. Yes I've got an external pump. I pulled it off today and checked it out. No damage or foriegn material in there. Filled gear teeth with vas, refit and turned motor over without plugs. Fit plugs and got oil pressure immediately (30 psi). This dropped to just above 0 when it warmed up. The gauge shows an immediate reaction to revs but drops to just above 0 on idle. Any ideas? The bloke next door says it could be the cam bearings but didnt explain that very well. He's a diesel fitter so not sure he knows what my engine should be doing.
I'm going to buy a mechanical gauge next week and see if I get the same reaading.
Regards
Coops
Thanks for the instructions. Yes I've got an external pump. I pulled it off today and checked it out. No damage or foriegn material in there. Filled gear teeth with vas, refit and turned motor over without plugs. Fit plugs and got oil pressure immediately (30 psi). This dropped to just above 0 when it warmed up. The gauge shows an immediate reaction to revs but drops to just above 0 on idle. Any ideas? The bloke next door says it could be the cam bearings but didnt explain that very well. He's a diesel fitter so not sure he knows what my engine should be doing.
I'm going to buy a mechanical gauge next week and see if I get the same reaading.
Regards
Coops
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Kevin Johnson
- Posts: 4
- Joined: Sun Jun 26, 2005 6:13 pm
- Contact:
Hi Coops,
It sounds like you fixed the original problem when you examined the relief valve (extremely high oil pressure that was actually breaking components).
What you are describing now simply sounds like an engine with a lot of miles on it. The oil will follow the path of least resistance and if your cam bearings (or other bearings) are heavily worn they will allow the oil to escape considerably faster. The bearings in an engine can be thought of as a series of controlled leaks. Many times people rebuilding an engine will change the rod and main bearings but leave the cam bearings untouched and then that will be a source of mysteriously low pressure. An engine can live, though, with oil pressure of 5 psi (say) at idle going back to the 10 psi per 1000 rpms rule of thumb.
Yes, a mechanical gauge is generally more accurate (I don't know if that is true when you look at modern electronic gauges though); just be careful when routing the oil tube through the engine compartment and then to the dash if you plan on leaving it permanently installed (keep it away from the exhaust manifolds or sharp edges that might rub against it).
I didn't mean to sound like I was giving you instructions
-- I make parts for many different engines and when I describe how to install them I try to include things that might go wrong (usually mistakes that I have made myself in the past!). 
Kevin
It sounds like you fixed the original problem when you examined the relief valve (extremely high oil pressure that was actually breaking components).
What you are describing now simply sounds like an engine with a lot of miles on it. The oil will follow the path of least resistance and if your cam bearings (or other bearings) are heavily worn they will allow the oil to escape considerably faster. The bearings in an engine can be thought of as a series of controlled leaks. Many times people rebuilding an engine will change the rod and main bearings but leave the cam bearings untouched and then that will be a source of mysteriously low pressure. An engine can live, though, with oil pressure of 5 psi (say) at idle going back to the 10 psi per 1000 rpms rule of thumb.
Yes, a mechanical gauge is generally more accurate (I don't know if that is true when you look at modern electronic gauges though); just be careful when routing the oil tube through the engine compartment and then to the dash if you plan on leaving it permanently installed (keep it away from the exhaust manifolds or sharp edges that might rub against it).
I didn't mean to sound like I was giving you instructions
-- I make parts for many different engines and when I describe how to install them I try to include things that might go wrong (usually mistakes that I have made myself in the past!).
Kevin
Coops wrote:Kevin
Thanks for the instructions. Yes I've got an external pump. I pulled it off today and checked it out. No damage or foriegn material in there. Filled gear teeth with vas, refit and turned motor over without plugs. Fit plugs and got oil pressure immediately (30 psi). This dropped to just above 0 when it warmed up. The gauge shows an immediate reaction to revs but drops to just above 0 on idle. Any ideas? The bloke next door says it could be the cam bearings but didnt explain that very well. He's a diesel fitter so not sure he knows what my engine should be doing.
I'm going to buy a mechanical gauge next week and see if I get the same reaading.
Regards
Coops
Kevin
Your advice is much appreciated. I have found the members of this forum all happy to share information, unlike several others sites I have abandoned due to their attitudes.
I realise my knowledge is limited so thanks for your patience and instructions. I've spent 28 grand on the engine so far and am very hesitant about trashing it. I dont want that to stop me having a go though.
Hope to see you on the salt.
Regards
Coops
Your advice is much appreciated. I have found the members of this forum all happy to share information, unlike several others sites I have abandoned due to their attitudes.
I realise my knowledge is limited so thanks for your patience and instructions. I've spent 28 grand on the engine so far and am very hesitant about trashing it. I dont want that to stop me having a go though.
Hope to see you on the salt.
Regards
Coops
To help out anyone else having similar problems I thought I'd better finish this thread with an explaination of what was going wrong. As soon as I finally got time, (5 months later), I bought a brand new VDO mechanical oil pressure gauge.
As I was removing my electrical gauge I noticed the fitting was a little loose on the sender. I tightened it up and what do you know, instant pressure, no more pressure spiking, no more erratic behaviour. I'm told this is why many engine builders wont use them as they are only as they lose accuracy according to the condition of the wiring, connections, harness, temperature etc. I almost got my engine pulled down to trace this fault.
I felt a bit stupid but my biggest fault was not touching, removing all the parts or tracing the fault properly. Everything LOOKED ok. But anyway, put on the mechanical gauge seeing as I already bought it and was interested in the comparison. It did show a slight improvement by 5 PSI. Niether here nor there I spose but goes to show there is some error still being caused by something. Anyone want to buy a VDO electric oil pressure gauge. Its as accurate as the person installing it is careful.
Regards
Coops
As I was removing my electrical gauge I noticed the fitting was a little loose on the sender. I tightened it up and what do you know, instant pressure, no more pressure spiking, no more erratic behaviour. I'm told this is why many engine builders wont use them as they are only as they lose accuracy according to the condition of the wiring, connections, harness, temperature etc. I almost got my engine pulled down to trace this fault.
I felt a bit stupid but my biggest fault was not touching, removing all the parts or tracing the fault properly. Everything LOOKED ok. But anyway, put on the mechanical gauge seeing as I already bought it and was interested in the comparison. It did show a slight improvement by 5 PSI. Niether here nor there I spose but goes to show there is some error still being caused by something. Anyone want to buy a VDO electric oil pressure gauge. Its as accurate as the person installing it is careful.
Regards
Coops