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Stephen Tashiro
11-06-2012, 2:56 PM
Before the days of Exhaust Gas Recirculation (EGR), did intake manifolds on automotive engines usually get a layer of carbon in them?

I've only taken apart engines that had EGR valves and one can see from the valves themselves that a lot of carbon comes through them into the intake manifold. But is the EGR system the main source of carbon? The PCV system seems to suck oil into the intake manifold. I suppose that would burn to carbon if the intake manifold gets hot.

Scott T Smith
11-06-2012, 3:42 PM
Before the days of Exhaust Gas Recirculation (EGR), did intake manifolds on automotive engines usually get a layer of carbon in them?

I've only taken apart engines that had EGR valves and one can see from the valves themselves that a lot of carbon comes through them into the intake manifold. But is the EGR system the main source of carbon? The PCV system seems to suck oil into the intake manifold. I suppose that would burn to carbon if the intake manifold gets hot.

Stephen, back in the older days many intake manifolds had ports through them for recirculation of exhaust gas; this was used to heat up the carburetors and also to operate the manual chokes. Intake manifolds usually had a heat shield installed on their underbelly's to keep oil from being converted into carbon on the areas near the hot ports.

Usually the intake runners were fairly clean with little if any carbon present. The exception to this was when intake valves started to get worn and allowed hot combustion gasses to leak past them, and the runners in the heads might carbon up a bit. Back in the 50's and 60's, it was not uncommon for engines to require valve jobs around 75,000 - 100,000 miles.

Mike Henderson
11-06-2012, 3:51 PM
Back in the 50's and 60's, it was not uncommon for engines to require valve jobs around 75,000 - 100,000 miles.
You're being way too kind to those older cars. Most of the ones I owned needed new valve guides at about 50,000 miles - and some sooner.

The symptom was a smoking exhaust. Sometimes you'd stop for gas, and when you restarted the car, you'd get a big cloud of white smoke. Embarrassing.

Cars are MUCH better today.

Mike

[And just for the info of people who didn't live through those days, what would happen is that the valves wore the inside of the valve guides. And when that happened, the vacuum from the cylinder on the intake stroke sucked oil from the rocker area, down between the valve stem and the inside of the valve guide, into the combustion chamber, where it was burned. When it got bad, you could burn a quart of oil every time you filled up for gas. That's why service stations used to check your oil. When was the last time you checked your oil in a modern car?]

ray hampton
11-06-2012, 7:30 PM
Mike

That's why service stations used to check your oil. When was the last time you checked your oil in a modern car?]

what is OIL

Dan Hintz
11-06-2012, 7:58 PM
what is OIL

It's that stuff you pour into the tube covered by the 710 cap.

ray hampton
11-06-2012, 8:07 PM
It's that stuff you pour into the tube covered by the 710 cap.

I know what a 410 cap is but what is a 710 cap