1998 Blazer

My oil pressure reads 40 when I start my car but as it warms up it drops down to almost zero. What is the problem, a bad pressure sending unit or is the pressure actually dropping as the engine warms up?

Pressure probably is dropping. GM is happy with 7 psi at idle when warm

You can try replacing the sender if you want, but it sounds like your bearings are worn about as much as one would expect for a car this age(how many miles?). How long has it been like this? If it was like that new, and is still like that you are probably ok for now. What oil do you use? Multi-vis or single weight? Oil pressure typically falls as engines warm up, and is at its lowest at idle. Does it go back up when you increase engine speed?

Typical aging GM engine oil pressure. Some people have joked that a GM engine is broken in when the oil pressure gauge acts like a tachometer. I wouldn’t worry about it. This is very common in an aging GM vehicle.

Thank you for your reply. That does make me feel better

This is what it seems like to me. I bought it with 115,000 miles on the odometer. I have been using multi-vis 10W40 Synthetic. My mechanic noticed it first but i thought I saw the gauge drop a time or two before. it does go up to about 10 - 15 when I race the engine at driving speeds.

I have 135,000 on the odometer now. Funny but I don’t hear any valves rattling or tinny knocking sounds…yet. Thank you everyone for your input I feel a little more comfortable with this situation to know that its a typical GM quirk. Aside from the usual high mileage rattles and thumps it seems to be somewhat reliable (knock wood).

I checked my 2000 Blazer (114k miles) this morning. Cold oil pressure is 60/40 psi (driving/idling). Once the truck has warmed up the pressure is 40/20 psi. This is according to the dash gauge which can be taken with a grain of salt.

Once the truck got to ~100k miles it started using a little oil between oil changes (5w-30 dino every 4-5k miles). The consumption is about 1/2 to 3/4 quart every 4k miles. Replacing the PCV valve lowered the oil consumption a bit. Have the oil pressure checked with an external gauge to rule out a bad sending unit or dash gauge.

Ed B.

I would want to be paid at a minimum 2 hrs labor for this job. Since this is the 4.3 V-6 the sender is back by the distributor and of course needs a special deep socket to take it off (or you could pull the distributor). What I am getting at is there will be a cost involved with installing a mechanical gague just to verify things. Myself, if the low reading is not associated with any engine noise I would not spend the money, if you have engine noise that can’t be explained, well you must start with pressure verification

I have the same '98 4.3L V-6, but in a 4WD extended cab S-10 with 158,000 miles. Cold oil pressure is about 45-50. Warm/hot engine runs about 40 and at idle drops to about 20. I use Mobil 1 5W30 and it loses about 1/2 qt. in 3000 miles. Compression is still good and it still runs great. I have never had a major problem. Replaced alternator once, a/c compressor under extended waranty, two batteries and it’s on it’s third set of tires. I guess that she’s just about broken in now, huh?

I would like to thank everyone for your replies. I feel much better to know that this is a typical situation with Chevy/GMC. Although I am more of a ford person I am truly surprised with the Blazer. I can’t afford to buy another car right now and looks like I’ll be taking this to 200K if I’m lucky. Thank you again to all!