4.3L question

[Muddytazz]

1989 4.3L (my sisters S10 blazer)
She'll start the blazer up, be driving and in about 30 to 45 minutes of driving her oil pressure gauge goes from 60 to zero. She'll pull over, shut the truck off for a couple minutes, start it back up, have good pressure again and drive for another 30 to 45 min. Is this sounding like a sender issue or maybe a clogged screen? I'm really hoping its not a bearing issue.

 

[tarussell]

Could be sender issues - a mechanical gauge will test that theory . Might also want to consider that the motor could be all sludged up and the oil is having a difficult time returning to the pan . Given enough time the oil slowly settles back where it needs to be and the oil pressure is restored until the pan runs dry again.
Just a thought ......
Tom

 

[Muddytazz]

It has the factory gauge, but I believe they are still electric and not mechanical. We've thought about draining all the oil out, putting in a new filter, dumping some diesel in instead of oil and run it for about 10 - 15 min and drain. Just to see if we can clean out the sludge.

 

[dyeager535]

I've *heard* of having some real issues if you try and dislodge serious amounts of sludge this way. All that junk ends up clogging all the return holes. (worse than they already could be)

I took the valve covers off my first 305, and scraped a good 1" of sludge out of it, after I bought it. I'd take that approach over dumping something in it to try and dislodge.

At least that is relatively easy...if it's not sludged up in the valve cover area, then it probably isn't anywhere else either.

You could always disconnect the fuel pump relay, and assuming the oil pressure switch still works, if the pressure DOES drop below approx. 5 psi, the engine will die. A bit dangerous/inconvenient depending on the driver, but if it's repeatable, stick to side roads and see what happens. Just another way of testing the gauge with stuff already present.

 

[Muddytazz]

Is there anything else connected to the factory sender switch or is it a stand alone? Could I just remove it and install an aftermarket gague and line? I might have one laying around.

 

[dyeager535]

Depends.

If it follows typical GM convention for that time period, either the gauge sender and oil pressure switch will be seperate units divided by a T, or seperate oil pressure taps on the blocks, OR, the oil pressure switch/sender could be a one piece unit. (3 wires to one combo switch/sender, vs. 2 wires to the oil pressure switch, and one to the sender)

Being an '89, it's pretty likely you've got a seperate switch and sender.

 

[Muddytazz]

Ok, where are the locations of said items to look for?

 

[dyeager535]

Assuming the 4.3 is similar to the 350 blocks, either next to the distributor, drivers side, and/or above the oil filter.

 

[Muddytazz]

Ok, will double check this out when I see my sister today

 

[lectric80]

On an 89 it will be down next to the oil filter on the drivers side of the block. These are famous for the amount of sludge they build up. My old 4.3 in my Astro would do the same thing until I finally killed it by spinning a bearing. When I tore it down for to switch things to the new engine, I couldn't believe the amount of sludge that was in it.

 

[MaxPF]

It's the sender. My truck did the exact same thing. My GM mechanic friend said that such failures aren't uncommon. I replaced it and sure enough it works fine.