Strange new exhaust smell

[Phil Payne]

> For about the past month, I have had a strange exhaust smell from my '92 100S. It smells
like burnt coffee beans (not exactly the odor, but that's as close as I can describe it). I
originally thought it was just some sunflower seeds that mice had stowed in the engine bay
that I attempted to blow out and happened to get onto the exhaust or other hot engine surface.
But upon closer inspection, the smell is definitely coming from the exhaust, and not the
engine bay. I have changed the oil in that time period (from 10W30 Syntec to 10W30 Quaker
State Higher Mileage) to see if it helps my oil consumption issues (~1 qt per 500 miles), so I
was wondering if it may have something to do with it. I have used this same Quaker State oil
in a Honda Accord and Plymouth Voyager, and they do not have this odor. Any ideas?

Burning coolant.  A head gasket leak is favourite.  "Acrid" is the best adjective, IMO.

You need to do two tests:

a) Pressurise the coolant system with the engine cold and leave the car for a while to see if
you have a minor leak.  Good idea to spin the engine with the plugs out after this test in
case you do get leakage into a cylinder that would otherwise cause hydrolock.

b) Once you're happy the system isn't leaking in general, top up the coolant with pure
additive (no water) and see if either the coolant level falls over time or the smell gets
stronger.

These leaks are sometimes VERY minor.  It takes only a very tiny amount of coolant to cause a
noticeable smell.  I've known cars run like this for years.  The greatest exposure is
increased bore wear - you often find on stripping a car for this that the factory
cross-hatching is still visible in the cylinders that have seen no leakage, and polished away
in the ones that have.

--
  Phil Payne
  http://www.isham-research.com
  +44 7785 302 803