Oil pressure gauge shows drop under load

[sshanky]

Hi,

I recently topped off the oil (and added some leak-stop suggested by the auto parts guy -- it looked safe, as it contained only types of oil). Before and after doing this, I noticed my oil pressure gauge showed low pressure but it was a bit sporadic. Now, it seems to be better at low loads, but when I'm accelerating hard, or going fast on the highway (65 or 75 or so), the pressure shows a drop. If I lift my foot from the pedal, even on the highway, the pressure climbs back up to about 1/2 way. Depress the throttle back to cruising position, and the pressure drops nearly to the bottom.

How can this be? the RPM isn't changing, so I'd expect the oil pump is still spinning at its same speed, so why would the pressure drop and climb like that?

Thanks

[SLOSpider]

Maybe the stop leak is messing with the sender, You sure its full of oil?

[vandor]

I'd change the oil to 20w50 and see what happens. I would not want stop-leak in the system, who knows what's in it and what it can do... If oil is leaking from somewhere change the gasket or seal. Yes, sometimes that takes a lot of work.

[sshanky]

I have a feeling the stop leak is messing with the sender, too. I checked the ingredients because I didn't want something that might block things, but he told me it only affects soft gasket parts, giving them a bit of softness and expansion that can help close the opening caused by dry or thin or brittle gaskets or seals. But I was doubtful and it does correlate. It's definitely time to spend some time fixing the leaks and giving the car the attention she needs.

[TX82FIAT]

Some of our cars have very inaccurate dipsticks. As you are driving you are moving more oil throughout the system. When you change the oil do two things. Fill the oil filter prior to putting it on (larger volume filters can make a difference in oil level). Add four full quarts of oil to the engine. Turn it over run the car for a few minutes. let the car sit for a little while and then check your oil level readings on your stick. I noticed the last time i changed the oil that my dipstick was actually off by about 1/2 to 3/4 quart. Therefore, i would be running with just over 3 quarts and have a good reading on the stick.

with that said, I'm not a big fan of oil additives such as stop leak that may temporarily swell seals. An oil change to clean that stuff out and possibly any other small debris in your oil is a good first step.

[kilrwail]

If you're relying on a stock electrical Fiat oil pressure gauge, that may be your only problem. Invest $30 in a mechanical gauge - it will tell you the real story.

[vandor]

If you're relying on a stock electrical Fiat oil pressure gauge, that may be your only problem. Invest $30 in a mechanical gauge - it will tell you the real story.

I disagree - I found the stock gauge to be accurate: high pressure at cold idle, low pressure at hot idle, and it rises with engine speed. The same on all my Spiders.
I also do not like the idea of a pressurized line full of oil in the passenger compartment! One of them split on a friend's car showering his leg with hot oil. He had to find something to plug the hole in the oil filter block 500 miles from home. Not fun. Oh, and most mechanical gauges are very cheaply made.

[sshanky]

So I wonder why mine is opposite yours...Mine doesn't necessarily fall with rising engine speed, but it falls with rising accelerator pressure (more accurately, output).

[kilrwail]

If you're relying on a stock electrical Fiat oil pressure gauge, that may be your only problem. Invest $30 in a mechanical gauge - it will tell you the real story.

I disagree - I found the stock gauge to be accurate: high pressure at cold idle, low pressure at hot idle, and it rises with engine speed. The same on all my Spiders.
I also do not like the idea of a pressurized line full of oil in the passenger compartment! One of them split on a friend's car showering his leg with hot oil. He had to find something to plug the hole in the oil filter block 500 miles from home. Not fun. Oh, and most mechanical gauges are very cheaply made.

Csaba - I'm not going to debate the points you have raised, but a mechanical gauge could be used temporarily as a test arrangement to determine whether there is something going bad in the engine. It would not have to be installed permanently. My electrical gauge began to give false readings that were very alarming.

[vandor]

Peter,

Oh, sure definitely. I've done that too.