Intermittent Burning Odor In Engine Bay

[EddieC]

Having an odd intermittent burning odor from engine bay.
The odd thing is if I work the truck harder like on a long climb then the odor prominently shows itself.
Tranny temperature is normal for what it has been in the past and the odor is more forward than that.
I'm not seeing any engine oil leaks in the engine bay and as noted the odor is not consistently there like an oil leak would be expected to be.
Also engine is not using more oil than usual which is about a quart between changes (5000 miles or so).
Power steering fluid is very old and has a burned odor and the pump had some seepage below the shaft that cleaned up and was slow to return but the high pressure line is damp near the crimped end.
Main and AC Belts were changed a few months ago as well as idlers (more recently). I haven't gone back to check the idlers.

Any thoughts?

 

[Big Mama]

Is it an oil burning smell, a burnt wire smell, an overheating smell, a brake pad smell? Any smoke? I’d try to hunt this down sooner than later. Check your battery and ground connections too.

You may notice it more going up a steep grade bc you’re going slower than normal. Do you see anything on your exhaust that may signal the location?

 

[EddieC]

Not motor oil burn smell. It's hard to describe. Perhaps between electrical and something else. It's not from the alternator and I suspected the PS area as that was the general location until yesterday is was on the other side. PS fluid does smell burned.

Also definitely not a brake pad odor and no visible smoke.

The dash gages don't show temperature or oil pressure any different than normal for the vehicle. The DIC trans temperature also shows consistant historical values.
The dash voltmeter does vary from about 12 to 14 volts at various times but that was deemed not abnormal in another thread.

The HVAC fan has started making slight noises at times/certain speeds but the odor, although sometimes in the cabin but less strong, is more in the engine bay. I might guess that the HVAC air inlet is drawing it in.

 

[Doubeleive]

Not motor oil burn smell. It's hard to describe. Perhaps between electrical and something else. It's not from the alternator and I suspected the PS area as that was the general location until yesterday is was on the other side. PS fluid does smell burned.

Also definitely not a brake pad odor and no visible smoke.

The dash gages don't show temperature or oil pressure any different than normal for the vehicle. The DIC trans temperature also shows consistant historical values.
The dash voltmeter does vary from about 12 to 14 volts at various times but that was deemed not abnormal in another thread.

The HVAC fan has started making slight noises at times/certain speeds but the odor, although sometimes in the cabin but less strong, is more in the engine bay. I might guess that the HVAC air inlet is drawing it in.

did a motor mount blow it's goo out? generally whatever they use in the mounts leaves a noticeable stain below it when they crack and it leaks out, that could be what you are smelling

 

[petethepug]

The bearing in the hvac fan can start to go and heat up from friction. That in turn causes the fan motor resistor to heat up which gives off the smell of electronic fajitas.

 

[jvanwanz]

I just had this issue with my '15 Yukon 5.3L. Valve cover gasket driver-side was leaking. Dribbled down to the exhaust manifold. Smoked enough where the HVAC sucked it into the cabin. Had the gasket replaced and no further issue since this past February.

 

[bill1013]

The plastic heater hose, where it goes into the firewall, may have a small crack. The engine RPM goes up and the water/coolant pressure goes up. A small leak, over time, becomes a major break. Hope this helps.

 

[petethepug]

Oh yea, had that happen before. That made quite a smelly smell. Just don’t keep driving it till all the coolants gone.

 

[EddieC]

Thanks for the idea.
This morning I rechecked the drive belts and two tensioners I recently replaced. No odd pulley movement (on anything drive related) or belt abrasion issues there.
The PS pump face is damp under the shaft. An obvious need to replace that and a weepy high pressure hose but there is no noticeable wobble in the shaft by gripping the pulley.
Idling in the driveway the odor is not noticeable.
No oil or coolant leaks including at the firewall as someone else experienced. The driveway does not show any leaks under the truck either.

Sniffing toward the source I tried to disconnect the radiator cooling fan on the predominant odor side but didn't leave it unplugged because it causes the other fan to max out and I thought it might do t harm. Both fans do run when called on.
One a test ride the odor seemed much less prominent but I can't imagine how disconnecting and reconnecting had that affect.
Next i removed and unplugged the suspect front hvac fan. That seems to have also greatly reduced the odor and also made the dash voltmeter much more stable, steady just over 14 volts.
I hadn't thought the odor was electrical but perhaps it is.
There is no odor from the alternator but it seems perhaps it is near the battery and coolant overflow jug and the "fuse-fusible" thing mounted on the firewall next to those things.
Does that fuse container open for inspection? It's the one that the red primary cable runs through from the alternator, battery and left fenderwell fuse box. From what can be seen it appears there is a bare copper fuse bar connecting two of the cables so I wondered what else is inside there.

I'll look at the motor mounts as suggested because one is in that area too.

One added thing noticed on this morning's run is that the oil pressure at speed seems higher than normal. I don't ever recall seeing 60 psi before. Off throttle or cruising it's back to normal 40 psi but the high is odd on a nice warm Spring day. Perhaps a filter change is in order to see if it might have an issue.