falling oil pressure

[dogaloo]

I recently purchased a 1989 GMC Jimmy 2.8 v-6 4x4 w/5-speed manual. It has 186,000 miles and it has some piston slap on hills when in a higher gear but seems to run just fine. It usually has 40psi of oil pressure in city or highway. However, I changed the oil with lucas oil and 10w-50 and drove it about 200 miles. Ever since then when I drive for a little while the pressure slowly falls until it eventually drops to the redline. When on the highway @ 60mph, the pressure holds at 20psi, but as soon as I get off and drive slower, it plummets to almost nothing. The truck still runs good but the temperature rises some above normal with the pressure drop. It has not overheated or died but the oil pressure has me concerned. Could this be worn out bearings? What can I do?

[maxwedge]

Welcome to AF, get a mechanical gage on it to confirm the dash gage, if correct this engine will need major internal work, especially with the " piston slap", which these engines did not have, more likely bearing noises.

[BlazerBoyLT98]

Sounds more or less like you have a rebuild on your hands. Good luck

[blazes9395]

When its running, if the guage drops to 0 do you hear any engine noise, or lifter clatter? Get a manual guage on there and confirm you oil pressure. If the guage is hitting 0 and its still running alright with no lifter clatter, chances are its not the engine, but rather the oil pressure sender. Why did you use 10-50? I honestly can't remember if they have a 10-50. First I personally don't like Lucas oil, but 10-50 I think is not a good viscosity for this engine. I would say to stick to more perferred viscosities for the 2.8. Also are you sure your hearing piston slap and not engine knock or denotation?

[bigd7315]

what brand oil filter and i would after check oil pressure with a` manual gauge try changing the oil and oil filter again using 10w30 or 10w40 and a acdelco oil filter considering acdelco is made by chevy for there vehicles