Well, it seems that the old blue truck is falling apart. I decided to keep her rather than trading her in and she's gone to h3ll ever since.

Y'all helped me with identifying & replacing the IAC and fixing the "wild vents" so I thought I'd ask about this.

This morning on my way to work I turned on my defroster due to a foggy window in the rain. I got a coolant odor and inside fog. I figure heater core but there is no wet carpet.

When I got home the truck's oil gauge starting moving back & forth between 40-60 or so (it's usually steady just above 40) and the RPM's starting started oscillating between 500-800 while idling. Could the oil sending unit cause the RPM problems also?

Is it a coincidence or could all of these things be related?

For the record, it's a 1997 Ram 1500 V8 5.9L Magnum with 185,000 on it.

 

Wet carpet or no, coolant in the defroster is a leaking heater core or hose.

I'd expect the erratic idle was causing the oil pressure fluctuation, rather than being caused by it.

I can't imagine a scenario in which a leaking heater core might cause the engine to idle erratically, but ya just never know. I'd approach them as separate problems.

 

@UnregisteredUser - thanks for the input. I just went back out, checked the oil (checked day before yesterday but you can never be too careful), warmed her back up and tried to recreate the problem without success. Damnit.

The oil pressure gauge trembles around 40 while idling, moving up & down just a bit sometimes, then it jumps to 50-60 when I rev to 2000 RPM. When i go back to idle it drops back to trembling around 40.

The trembling & large(ish) jump is relatively new. It started about 2 weeks ago when I had my tranny & differential serviced. I don't see how that could be related, though. Before then the needle was pretty steady just above 40 most all the time.

Is the trembling and small oscillations when idling & jumping when revved considered normal?

 

BTW, is this the oil sending unit and is that the same thing as the "oil pressure switch"?


**clickable thumbnail**

It's on the rear of the engine on the passenger side of the distributer cap.

 

There are three sure ways that I know of to make an oil pressure gauge oscillate like that: Overfill the crankcase so you're pumping foam, foul the oil filter so the relief valve flutters, or wait around for the sending unit to fail.

I suppose that if your crankcase isn't overfull you could hook a mechanical oil pressure gauge to the engine to see if it, too, wiggles like your electric gauge. (If it oscillates, it's probably the filter; if it doesn't, it's probably the sending unit.) Were it mine to do, though, I'd just do an oil and filter change, and if the gauge is still oscillating, replace the sending unit.

That is in fact the critter you're looking for in the photo.

Edited to add: It's normal for the oil pressure to increase with engine RPM, but on these engines it should be more of a rise than a jump.

 

With the engine warmed up & then rested for about 5 minutes, I'm right at the top line on the dipstick so I don't think that's overfull.

Now that you mention the filter...

I've used synthetic oil for years, generally Mobil 1 and an O-Reilly's store brand filter. 5500 miles ago I accidentally bought synthetic blend so I used it. 500 miles ago I switched back to full synthetic (store brand) and a Mobil filter.

I didn't notice the needle tremble before today and I didn't notice any difference in my pressure before my tranny service 2 weeks ago but I can't swear it didn't start when I last changed my oil and I didn't notice it at that time. Around that time I was fighting with my IAC and it's faulty replacement so I was preoccupied.

From what you say, I could have a bad Mobil filter. Could the O-Reilly's synthetic oil be a factor also?

If so, that was one helluva bargain.

 

Since the crankcase isn't overfull, it's almost certainly either the filter or the sending unit. I can't imagine the oil itself playing a part.

 

Thanks! I will try

1. draining a little oil out then recheck (can't hurt)

2. change the oil & filter (again...)

3. replace the oil pressure switch (hope not)

In that order. I'll post how it goes tomorrow.

 

supposedly when it jumps, the switch is bad. my oil pressure gauge follows my tach when i drive. I replaced the switch and it does the same. (thought it was a $10 fix, turns out my oil pumps screen is clogged or pump is going out).

 

Well, first thing this morning I checked my engine cold. It showed above the "safe" zone on the stick. I drained some oil out of the engine while it was cold. It showed to be about 1/3 the way past the bottom "safe" line on the stick. I cranked her and the trembling oil pressure needle stopped but the oil light flickered on when I test drove it and came to a stop to turn into my driveway. I added back to full on the stick and the needle started trembling again.

I didn't change the oil again because I was fighting with my distributor cap all afternoon.

I really didn't expect the oil light to flicker on with the oil level in the "safe" zone on the stick. I generally check my oil after I warm the engine to operating temp then turn it off & let it sit for 5-10 minutes. After UnregisteredUser's comment about an overfull crankcase, I got to wondering just how much difference it makes checking the oil in a cold engine & a warm engine.

Could a full crankcase in a warm engine be, in reality, overfull? It's never given me trouble before. Could 1/3 the way into the "safe" zone in a cold engine really be low on oil once the engine is warm.

Or is my oil sending unit just bonked?