EGTs.Who here is actually monitoring? - Page 2 - PeachParts Mercedes-Benz Forum

87tdwagen · #16 05-29-2019, 07:03 AM

OM603 here, used test port on exhaust manifold for k1 probe. Gr es at gauge for combustion health monitoring, was a good indicator that my catalytic converter was getting clogged with soot as normal EGTs were geting higher.

Maximan1 · #17 05-29-2019, 08:27 AM

Quote:

Originally Posted by Shern

Then shouldn't that affect coolant temperature?
How could a piston melt without affecting the temperature of the block?

I'm trying to imagine a scenario whereby one is able to run with dangerously high EGTS (piston liquifying) and have no indication of this on their dash temp gauge.

This is totally new stuff to me and I really appreciate the explanation!

Disclaimer - I do not know how the piston in my photo melted. I got the engine that way. The guy I got it from told me that it just stopped running on the freeway, no warning or any overheating on the gauge.

There is also another user on this forum that recently had his 300D do the same thing, he also said that it just started running badly after a freeway run IIRC. No indication of a problem otherwise.

EGTs spiking when you're running at high RPM will cause the piston to melt like that. If you were running high EGTs for an extended period, you would see it in the coolant temp. I am assuming that the EGTs spiking for whatever reason would cause the catastrophic piston failure before you see it in the coolant temp because it would take some time for the excessive EGTs to heat the ~2 gallons of coolant to a degree that would be noticeable on the gauge.

Shern · #18 05-29-2019, 09:04 AM

Ah-ha, understood. I appreciate the explanation, gents.

Diseasel300 · #19 05-29-2019, 09:55 AM

Quote:

Originally Posted by Maximan1

EGTs spiking when you're running at high RPM will cause the piston to melt like that.

High EGT's will warp the head, cook the turbo, burn valves, or crack manifolds long before pistons melt. If EGT were the cause of your piston failure, you'd see similar damage to ALL of the pistons. I'd suspect an injector failed and roasted that cylinder. Yes, EGT would be high compared to normal in a case like that, but likely not as high as running rich and causing high EGT as a result of load.

Maximan1 · #20 05-29-2019, 10:40 AM

Quote:

Originally Posted by Diseasel300

High EGT's will warp the head, cook the turbo, burn valves, or crack manifolds long before pistons melt. If EGT were the cause of your piston failure, you'd see similar damage to ALL of the pistons. I'd suspect an injector failed and roasted that cylinder. Yes, EGT would be high compared to normal in a case like that, but likely not as high as running rich and causing high EGT as a result of load.

The other pistons had old damage from a turbo that cane apart, I wonder if there was damage to the piston from earlier that weakened it before and an EGT spike finished it off. I didn't even notice the damage on the other pistons until I soaked them in cleaner/degreaser for a few hours and scrubbed, so there was a good amount of carbon covering them.

I have had many people tell me how weak cast pistons are compared to forged, and that high boost/high EGTs will melt them, but I'm not an engine builder by any means.

Dan Stokes · #21 05-29-2019, 10:44 AM

Quote:

Originally Posted by Diseasel300

High EGT's will warp the head, cook the turbo, burn valves, or crack manifolds long before pistons melt. If EGT were the cause of your piston failure, you'd see similar damage to ALL of the pistons. I'd suspect an injector failed and roasted that cylinder. Yes, EGT would be high compared to normal in a case like that, but likely not as high as running rich and causing high EGT as a result of load.

To carry on from this post - when I installed my big turbo (T3/T4 hybrid) my EGTs were approaching 1200 at the end of the track running 20 PSI boost. As I added boost the EGTs DROPPED. Other Diesel racers have noted similar results. Overfueling will raise EGTs and adding enough air to satisfy the available fuel in the combustion chamber lowers the EGTs even though power output goes up (in my case, considerably).

Dan

Maximan1 · #22 05-29-2019, 10:47 AM

Quote:

Originally Posted by Dan Stokes

To carry on from this post - when I installed my big turbo (T3/T4 hybrid) my EGTs were approaching 1200 at the end of the track running 20 PSI boost. As I added boost the EGTs DROPPED. Other Diesel racers have noted similar results. Overfueling will raise EGTs and adding enough air to satisfy the available fuel in the combustion chamber lowers the EGTs even though power output goes up (in my case, considerably).

Dan

So, rolling coal/adding fuel will raise exhaust temp? It seems counter-intuitive, especially for someone coming from a gasoline powered car background.

tjts1 · #23 05-29-2019, 10:59 AM

Quote:

Originally Posted by Maximan1

EGTs spiking when you're running at high RPM will cause the piston to melt like that. If you were running high EGTs for an extended period, you would see it in the coolant temp. I am assuming that the EGTs spiking for whatever reason would cause the catastrophic piston failure before you see it in the coolant temp because it would take some time for the excessive EGTs to heat the ~2 gallons of coolant to a degree that would be noticeable on the gauge.

On the contrary, high EGTs happen when running high load at low RPM for an extended period of time. My 300D will happily climb a long freeway hill at 65-70mph in5th gear but EGT will creep up above 1000. Drop it to 4th and 3500rpm at the same speed and load and EGT stabilizes down to 800. As a rule of thumb, the more air you can flow through the engine for a given load, the lower your EGT will be.

Diseasel300 · #24 05-29-2019, 11:18 AM

Quote:

Originally Posted by Maximan1

So, rolling coal/adding fuel will raise exhaust temp? It seems counter-intuitive, especially for someone coming from a gasoline powered car background.

Correct. Diesels always run lean, even when rolling coal they're still burning lean. More fuel = hotter exhaust for a given amount of intake air charge. Ideally, a diesel engine will NEVER smoke in a perfect world. A small puff or light haze under hard acceleration is normal, but smoke is less than ideal. Those idiotic Bro-Dozers you see rolling coal are just cooking their own engines to an early death and making obnoxious noise without any performance gains to show for it.

Maximan1 · #25 05-29-2019, 01:35 PM

Quote:

Originally Posted by Diseasel300

Correct. Diesels always run lean, even when rolling coal they're still burning lean. More fuel = hotter exhaust for a given amount of intake air charge. Ideally, a diesel engine will NEVER smoke in a perfect world. A small puff or light haze under hard acceleration is normal, but smoke is less than ideal. Those idiotic Bro-Dozers you see rolling coal are just cooking their own engines to an early death and making obnoxious noise without any performance gains to show for it.

Gotcha, thanks for the info. I've still got plenty to learn about diesels, everything I owned or repaired prior was gasoline powered. The more you know!

Dan Stokes · #26 05-29-2019, 02:15 PM

Quote:

Originally Posted by Diseasel300

Correct. Diesels always run lean, even when rolling coal they're still burning lean. More fuel = hotter exhaust for a given amount of intake air charge. Ideally, a diesel engine will NEVER smoke in a perfect world. A small puff or light haze under hard acceleration is normal, but smoke is less than ideal. Those idiotic Bro-Dozers you see rolling coal are just cooking their own engines to an early death and making obnoxious noise without any performance gains to show for it.

First of all - X2!!!!!

Also, my Dodge/Cummins sometimes puffs a bit from a dead stop depending on conditions. The reason is that the tuner (an Edge) shoves a tad too much fuel in before the turbo has spooled up. Remember, the main driver of a turbo is NOT exhaust gas pressure, it's exhaust heat. Once the exhaust gets hot it expands upon cooling (when it leaves the combustion chamber) and that expansion is the main driver for the turbo with exhaust pressure taking a more minor role. So when sitting at idle (say, at a light) the combustion chamber temp drops and upon accelerating (the light just changed) it takes a couple of seconds for the heat to come up and drive the turbo.

Mutt the Race Truck has this in spades. With the big turbo it takes more energy to spool it up meaning it needs more RPM and more load for that to happen. The big injection pump is fully manual (no electronics, sensors, etc.) so it sends fuel as soon as I hit the loud pedal and the turbo has to get spooled for the smoke to quit, which it does. Usually. Sometimes it takes several seconds for the fuel delivered early in the run to clear out so it rolls coal for a while. Wish that didn't happen but at least I know why.

Dan

OM617YOTA · #27 05-29-2019, 05:38 PM

I've got no alda and otherwise stock. Normal driving, no smoke. Mash the pedal from a stop or low boost condition and yeah it'll blow black for a bit. I also get a black puff when blipping the throttle to rev match while down shifting. Still need to rebuild my turbo, that'll help a lot.

Dubyagee · #28 05-29-2019, 06:07 PM

Mine puffs black on launch but clears right up. Wonder if theres a way to intercool these 87 300Ds. I already have a Kubota oil catch can to keep the oil build up out of the intake path.

87tdwagen · #29 05-29-2019, 06:13 PM

Quote:

Originally Posted by Dubyagee

Mine puffs black on launch but clears right up. Wonder if theres a way to intercool these 87 300Ds. I already have a Kubota oil catch can to keep the oil build up out of the intake path.

Yes they can be intercooled. Search this forum as several members have done so and shared the how to, including myself for my 87. There are several write ups on what people used. The small intercooler I used was good for about a 3psi drop in boost and about 150 degree drop in EGTs

Simpler=Better · #30 05-31-2019, 02:44 PM

Quote:

Originally Posted by OM617YOTA

My EGT probe is pre-turbo, I run ~600 ish cruising flat ground at 60 mph. Truck has the aerodynamics of a brick and tires more suited to offroad use than low rolling resistance on pavement.

Pulling a hill at WOT while hauling a load, it can get to 1100 easily and then holds there.

My w123 was very similar.