BuickNut Posted June 16, 2003 Share Posted June 16, 2003 I got my '73 out of mothballs for a few weeks, then put it back in. Engine ran fine for the first few weeks, changed the oil and filter before starting, and pressure was fine for the first few weeks. Just before I put it back in storage, the oil pressure would drop terribly low when I was doing highway speeds (65 mph), or when I jumped on it, and then return to normal pressure when doing 40 mph.......might it sound like an oil pump problem ? Oil level was fine, and the oil and filter was changed twice the first few weeks it was on the road......... Thanks. Link to comment Share on other sites More sharing options...
Guest Posted June 16, 2003 Share Posted June 16, 2003 I would drop the oil pan (assuming you can get it off without tearing the whole car apart) and "mike" / "plastiguage" a couple of the rod bearings. It is always a good idea to drop the oil pan and clean it out on ANY old car.Assuming you have checked everything else out, the oil was of the proper level and viscosity (10W-30) and you find the bearings are fine, my suspicion is you have some kind of guage issue. Have you tried "monitoring" your oil pressure guage, by "T eeing off" from the hole in the block where the oil pressure SENDER is, and watching things with a whole separate line and oil pressure guage..? Link to comment Share on other sites More sharing options...
Guest Posted June 16, 2003 Share Posted June 16, 2003 could be oil foaming or you've got some water condensation in the engine, and then the oil pump "goes loopy" were it pumps the h2o.I run straight 30 weight in all my cars. The oil dose thin a bit, but never had a problem. Link to comment Share on other sites More sharing options...
Terry29-26 Posted June 17, 2003 Share Posted June 17, 2003 Did you change the oil filter? Not sure about your buick but some eng.s run with releaf valves or bypass valves in the filter. If this is the case with your car it could be that you have a bad filter. Simple fix if all you have to do is change the filter. Make sure you have the correct filter for your engine. If everything was working fine before the oil change look for the simple answers first. I would never drop the pan untill I checked the filter. Link to comment Share on other sites More sharing options...
The Old Guy Posted June 17, 2003 Share Posted June 17, 2003 The bypass valve only bypasses the filter. It should not change the oil pressure. The only thing to cause a pressure drop is either too much bearing clearance,or not enough volume. Link to comment Share on other sites More sharing options...
BuickNut Posted June 17, 2003 Author Share Posted June 17, 2003 The filter was changed both times with the oil change. The second oil/filter change improved the pressure some, but it still is very low upon acceleration and highway speeds. I'm going to try and put in a new oil pressure sending unit and see if that migh not be the problem.......guess I just can't beieve the oil pump could be fine one day, and kaput the next...... Link to comment Share on other sites More sharing options...
Terry29-26 Posted June 17, 2003 Share Posted June 17, 2003 Joe;;You may be correct for the application in question but;;;;; if the wrong filter is used there can be all sorts of problems. If bypass and full flow filters are inter changed strange things happen depending on the engines oil system.!929 Buicks have a partial full flow filter. Oil is directed to an orfice that restricts the flow to the filter which has a by pass valve in case the filter gets pluged. When the by pass valve opens the flow is no longer restricted by the filter element and the oil preasure drops. Oil that leaves the filter oils the valve train and does not lub the crank nor cam. If a hole developes in the filter element and oil is not restricted by it the oil preasure drops. Misslabled canisters do happen ; you can't tell a book by its covernor nor can you tell whats inside a filter from the out side. If you would like to discuss this further please Email me. Terry29-26 Link to comment Share on other sites More sharing options...
Guest Posted June 17, 2003 Share Posted June 17, 2003 I built a '64 425 nailhead engine awhile back and had an odd problem. All seemed OK except I noticed that during deceleration the oil pressure would dip for a moment then return to normal. As the miles added up it became more noticable, but the presure wasn't that low during the dips. Miles later the pressure was lower but still good except for those dips. Then one day after driving a few miles on a freeway and stopping at the exit of an off ramp the oil pressure at idle was scary low. A tiny bit of throttle and it would bound back to very good pressure. Now it would go up and down while raising RPM at a constant rate. Raise RPM and up it would go ... to a point, and then the pressure would drop while still going up in RPM. While still raising the RPM it would come back up. It just would not stay consistant. During coast down you could watch it go up and down until just before idle when it would bouce up to good pressure, but then right at idle it would go back down to scary low. People told me I had loose bearings ... seemed to me that to much clearance would mean constantly low pressure. Not up and down all the time. Got my self a cheap electric oil gage and by-passed the mechanical gage I was using to see if it was the gage ... it wasn't. Since it seemed to very so much at different RPMs I decided it may be the pump. It seemed to act like the shaft in the pump was vibrating at certain RPMs and causing cavitation or something. Changed out the pump and things are great. Link to comment Share on other sites More sharing options...
NTX5467 Posted June 18, 2003 Share Posted June 18, 2003 The basic pressure output of the pump is governed by the relief valve spring in the pump itself. The spring tension governs high, low, or medium pressure at the specified rpm level. This has nothing to do if it's a "high volume" pump or a regular pump.Oil viscosity can have an impact, but I suspect that as long as it's reasonably close to what it needs to be to keep the bearings supplied without causing them to knock (giving consideration to the earlier times when 10W oil might be used in the very cold winter climates and thicker oil in warmer weather) the pressure should be in specs. If it's too thick, it will take too long for the pressure to build to specs (called "pumpability" in the cold weather specs).As mentioned, the bypass valving in some filters is there to not (hopefully) blow the filter housing off of the engine if the filter should become totally or significantly clogged. No more, no less. I think that relief valve is set to about 10psi pressure differential. In some later model filters, there's also an "anti-drainback" valve to keep the oil from (supposedly) draining out of the oil galleries in the block when the engine is stopped. This is supposed to help get oil flowing quicker to the bearings and such upon startup and maybe address some bearing clatter issues before things get all pressured up.As I recall, the oil pump kit for the Buick V-8s of that vintage is just a new pair of gears and a new end plate that they run against. It's a softer steel, I suppose so it is designed to wear first rather than the oil pump gears. In some engines, the oil doesn't exactly flow through the supply lines smoothly and that can place varying loads on the pump itself, which might tend to vary the pressure some and also cause "spark scatter" with the engine timing where the distributor drives off of the oil pump shaft.In earlier engines that were not specifically designed for oil filters, they did filter only part of the engine oil via the mentioned restrictions and such. By filtering only the excess oil via a fixed restriction, it was easy to adapt to the existing oiling setup in the block. The "full flow" filter arrangements came later as all of the oil was filtered as the filters were a part of the oiling circuit instead of being an "add-on" situaiton.Those oil pressure wild variations mentioned certainly sound unusual. I concur that if it was due to internal bearing clearances (main, rod, or camshaft) that they should be consistent and relative to engine temperature and possibly rpm.Perhaps the pressure relief spring was in the process of deteriorating or had broken? Combined with normal wear on the thrust plate in the pump, possibly that might explain the sporadic variations? As mentioned, it's always good to get a "second opinion" with a different gauge setup.Enjoy!NTX5467 Link to comment Share on other sites More sharing options...
The Old Guy Posted June 18, 2003 Share Posted June 18, 2003 I just remembered a situation I encountered some years ago with my daughter's Buick. She also had a problem with oil pressure,and when I pulled the pump cover, I found a small piece of wire jamming the relief valve open. It looked like a piece of welding wire,and probably came from the filter. I removed it and the pressure came back to normal. Link to comment Share on other sites More sharing options...
Guest Albert Posted June 18, 2003 Share Posted June 18, 2003 A friend of mine had a problem years ago with low oil pressure, was caused by the plastic off the timing gear plugged up the screen intake for the oil pump.. Link to comment Share on other sites More sharing options...
BuickNut Posted June 18, 2003 Author Share Posted June 18, 2003 Thanks for the input everybody....... Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now