oil presseure

[hadaveha]

i have a 1986 gmc s15 blazer 2.8 as it starts to warm up say 20 minutes or so, the oil presure starts to drop, and then if u cut the enginge off its very hard to get the engine to turn over, any ideas have heard looking at a motor job god i hope not

[Sparky2263]

As far as oil pressure, the gauges are notoriously inaccurate. They are okay at trends, but not very good at specifics and the oil sender is very prone to failure. An oil pressure test with a known good mechanical gauge is the best bet.

Doubt it's related to the cranking issue though. Okay cranking when cold but slow cranking when hot is indicative primarily of a bad starter. Could simply be a bad connection or battery, or even advanced timing, but doubtful.

[hadaveha]

we checked the oils sending unit, it checks out fine my mechanic told me he thought it was loosing compression when it warms up, therefore the oil pressure drops, but i dont understand there is not one bit of smoke, we allso checked the timing we r spot ont with that, i may need a motor job just hopeing to make sure its not anything else

[Sparky2263]

Compression is not related to oil pressure. Compression increases with a warm motor as the rings do a better job of sealing.

Sounds to me like an oil pressure test (not a sending unit test) and a compression test are in order. You haven't said it's making any noises and it's not smoking, so I'm curious as to why the thinking is you may need an engine?

[hadaveha]

well i may not i kinda went into panic mode, what happend was i noticed that when the truck is cold it seems to have too much oil pressure, when its warm not enough, so i thought it was the timing but the timing is spot on, it doesnt smoke a bit and the only noice is a small amount of valve tick wich im sure could be cheap gas, so when i took it to my mechanic he said that the truck is loosing compresion as it warms up, and that he took a compression check, but i didnt se him doit, i no the guages or not very trust worthy, but i pretty sure the added oil prsseure when u shut it off is what makes it so hard to turn over, but wouldnt low compression make it easy to turn over. by the way thanku so much for your time and help

[Sparky2263]

took it to my mechanic he said that the truck is loosing compresion as it warms up

added oil prsseure when u shut it off is what makes it so hard to turn over, but wouldnt low compression make it easy to turn over.

You have little to no oil pressure during cranking. Besides, as you said, a warm motor has less oil pressure at idle than a hot motor.

Bottom line, you need specifics your current mechanic isn't giving you. Such as compression test results and oil pressure test results.

I'll also add in a charging and cranking systems test. But, any mechanic worth his salt charges for the above tests. It's called labor, and I don't put much value in cheap/free labor. Don't get me wrong, my buddies benefit from my 24+ years as a mechanic. But my customers aren't my buddies, they're my customers.

[hadaveha]

i have allready payed this clown 90.00 bucks and i only know that he is quessing ill take it somewhere and get someone to do a copression test, if when u give it a oil pressure test and it is actually low that shouldnt equal a engine job should it

[Sparky2263]

Honestly, if it's running good, compression isn't a worry. I'd do an oil pressure test to verify the problem there. As far as the hard cranking hot, I'd be doing a cranking and charging systems test.

A compression test is only called for if it's actually running bad.

[hadaveha]

thnku for your help, id be glad to help u allso but i dont really know anything haha thnks

[Maximus]

Sounds like some shady/lazy mechanic trying to give you the shaft in the effort to get paid for a big job when in reality it's probably something simple.It's a**holes like that who give good techs a bad name.There are plenty of them around here that I have had to fix their screwups.And stock gauges are not always accurate even in latemodels.A good mechanical gauge is the best way to find out for sure what the pressure really is.Do what Sparky suggested you to do.

[hadaveha]

ok guys i need to say im sory to the mechanic the oil pressure is low, compression is great, valves r starting to chatter, looks like the main baring, i think if i use a little heaver oil, i can get some more time from what i understand some of these 2.8's ran for ever on low oil pressure, but i think eventually im defently looking at a new motor, i think when the time comes i will try to go with something other than a 2.8. thnks for all u guys help