Funny Oil Pressure gauge question...

Hi,
A general question about my grandfather 86 Dodge Caravan...
When you first start it up the Oil Pressure Guage (its a basic analog dial like the speedometer, engine temp and such) goes up to 3/4 mark between High
and Low pressure.
After driving it for 5 miles or so, it slowly floats down to half way between High and Low pressure.
After that if the speed drops below 20 or 30mph it settles down to 1/4 between High and Low pressure. It tends to stay there as long as the speed stays below 30 (I notice it when I'm stuck behind a snowplow for a long distance) but it goes back up to half way once I get back up to 50mph+
I check the oil levels every so often just to make sure and it hasn't moved nor are there any leaks. Am I worrying for nothing or should get a mechanic to check it out?
Its fine other than this, and everything else runs and drives nicely. Is it something to worry about or should the pressure guage move like this in all vans?
thanks for any advice!
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1986. How many miles?
Two dynamics are happening here: As the oil heats up it flows through the system better, even though it is (hopefully...) a multigrade and your Grandpa doesn't use straight 30 weight, the guage will go a little lower.
The other is that things are wearing out in the bottom end of the engine, and 'allowing' oil to flow in more passages than the original manufacturing called for. Things to look for are piston bearings and rods, rings (esp if it 'puffs' when started) and a weak oil pump.
I mostly drive Toyotas. I have driven a Corolla like this for about 8 years. Just keep changing the oil regularly. I don't think an '86 is worth a $6-1200 rebuild, unless the rest of the thing is in exceptional condition.
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Oops, I meant to say 1996 about 110k. Sorry if this confuses the issue. Same advice?

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Interesting. I suppose until some other symptom develops I'll just tell him to keep driving it.
I'd ask a mechanic to take a look at it, but as you said its not worth doing any major work to it. Its really a beater car so I'm just going to keep my fingers crossed.
You mentioned oil grades.
Does it really matter if he uses a synthetic or 10w30. I don't really know much about these things but I assumed synthetics were what you put in performace cars. What do you think? How often should I be changing it?
-thanks a bunch,

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I had the very simialr problem with my 89 dodge dynasty. Initailly the oil pressure scale was between half and 2/3; Laterly It dropped to 1/2- 1/3 range. I have a mechanic check the pressure, and he told me the pressures are ok but something wrong with my intrumental panel. I drive the car for about 20k like that. I donot know if it is realed but, my odometer stop working, and fuel level gauge interminently stop working. I think i need to change my instrumental panel. ($15 at a local junk yard)
Lately, I start to get leak from crank shaft seal. I donot know the low oil pressure is due to about the go bad oil pump seals.
I have 208 kmile (the odometer stopped at about 6 months ago. )
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My '94 Caravan 3.3 and my '90 Dakota 3.9 both read low oil pressure at operating temp. I think they're inaccurate. I thought I'd seen it mentioned in this discussion room several times that Chrysler oil pressure gauges were notoriously "not-dependable."
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The problem was oil pressure sending unit leaking and giving false readings, if you think it is wrong check pressure/replace the sending unit
Glenn Beasley Chrysler Tech
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Do you use very thin (low viscosity) oils.
These can go through your system without too much pressure needed so the sensor reads to low an oil pressure.
my $0.02
Dennis
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"Do you use very thin (low viscosity) oils. These can go through your system without too much pressure needed so the sensor reads to low an oil pressure. my $0.02 Dennis"
I use the specified oil weight in both vehicles. However, per a suggestion in a Dodge Truck discussion room, I switched my Dakota 3.9 to Mobil 1 synthetic, as some posters said their oil pressure came up to normal upon switching to that, which I thought sounded rather lame. Of course it made no difference. BTW I'm in agreement with Glenn about using conventional oil since you're flushing out the impurities more often by draining it at 3K miles, plus I think there's additional benefits in raising your vehicle up every few thousand and checking out other things underneath and underhood.
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snipped-for-privacy@webtv.net (James Goforth) wrote in

the
switched
vehicle
I used to work for Kroon-Oil a lubricating oil and -grease producer in the Netherlands and I cannot stress enough to follow the guide lines given by the car manufacturer. If they prescribe mineral oils with certain intervals then there is absolutely no poblem with these oils. Synthetic oils are more expensive, but could last longer intervals.
But mind you, there is a quality difference in engine oils. (at least here in Europe) The cheap, (mostly) mineral oils offered under own brand is often a qualitatively lesser oil. I always say there is no BEST oil for your car, all you need is the RIGHT oil for your car.
Cheers,
Dennis
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I agree Maxpower and James. As you may know, oil pressure will increase as your engine revs higher. I don't think it's a major problem myself. FYI, I personally don't think synthetic is that great. And once you switch to synthetic, you're pretty much stuck with. It also costs a lot more.
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On Thu, 16 Feb 2006 18:04:51 -0600, James Goforth wrote:

I am also suspicious of the oil pressure relief valve that is located in the oil pump. Usually a spring and ball bearing type valve, designed to open under high pressure to keep from blowing out seals. Once the valve is open and the spring gets hot, it does not shut like it should. If you ever pull the pan, check the valve, and replace the spring with something a bit stronger. Should allow for higher pressure before opening, though not to strong or you will blow your seals. OvO
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analog
way
1/4
for
to
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get
nicely.
like
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exceptional
I do not use synthetic oil, I change mine on all my vehicles at 3k. that's good enough. Dirt and heat causes problems and keeping those elements away will cause the engine to last a long time. If an engine is already worn out or causing problems I don't believe any kind of oil will help it out.
My opinion only Glenn Beasley Chrysler Tech
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On Thu, 16 Feb 2006 20:46:43 -0500, maxpower wrote:

I've only used Synthetic in one car, and really didn't notice a difference. I change at 3,000 also, and have had a lot of high-milage engines.
I also substitute 1/2 quart for Marvel Mystery oil. I started doing that a long time ago, and my engines usually go 30,000 beyond the point similar engines start showing wear!
--
In the grand scheme fo things...
What difference does it make?
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