Outer Limits 4x4 Board

Hi all Im new to this forum, I own a 2.8LT intercooled Diesel 4runner If any one can help me in understanding how EGT's can damage my engine and what to look for or modify to make sure it never causes any damage to my newly rebuilt engine. I would be much obliged

cheers

Well....motors are made of alloys and steel, which will melt if it gets hot enough. Alloys usually start melting around 600 degrees...but the motor usually hs oil squirting underneath and water all around the cylinder and fresh cool air coming in b4 the next injection...so it keeps cool enough.
If you want power, you turn up the diesel, but more fuel equals more heat, and if you go overboard....oops.
In comes the EGT...when pre turbo exhaust temperature reaches 700 degrees, its time to nack off or change down a gear. better to know than not....post turbo would be somewhere around 550 for the 700 pre temp.
Andrew

You could write pages on this but in breif;

More fuel(diesel) means more heat as there is a bigger bang, more heat means more power, the pison is pushed harder and for more crankshft degree of rotation, more heat means potentially damaged bits(pistons, heads), the burn time is longer so fuel is still combusting as it leaves the exhaust port and there is a greater portion of unburnt fuel and poorly combusted fuel (black smoke). Diesel is the opposite to petrol in that(talking generally) more petrol means cooler combustion(there are limits).
To tune a diesel you are adding fuel to the point where a number of happy mediums are satisfied depending on your application. Its visible smoke and heat vs power. A short course comp truck might run EGT's of 600 degrees, but power is only applied for short bursts and engine longevity is often not the main concern. A heavy towing vehicle that maintains high loads for long periods would be better suited to 450 degrees. This is by no means hard and fast. but I hope it helps. You can usually make more power by adding fuel, the issue is how much before you start causing damage to be done.
Joel

You see the skyline boys running 30 psi for a 1/4 mile...their egt is what they run off, when it starts glowing they back off or call a towtruck....a friend alloy coated his crank on a gtr32....bugger....fuel pump gave up and it ran lean...
If you set things to make power, you need to keep an eye on it....whereas as Joel said....450 will go all day every day up hills with avan on the back.
You can measure the egt after the turbo or before it....there is roughly 200 degrees difference in the two positions...

so if the exhaust gases are 700c leaving the cylinder head, and the actuall temp of the radiator coolant is 90c what is the temperature of the metal in the cylinder and exhaust manifold?
and if that super hot gases are leaving the head wouldnt any damage occure in the turbo, because the intake is getting fresh cool air every combustion stroke, or does the whole engine/every moving part heat up way too quick for the cooling system to cope and cracks occur quicker than blink of an eye and continue to grow untill a fault develops

thinking it through now, yes we want to lower egt, so big bore exhaust is on the list, expell hot gases quickly, I have noticed that my floor gets very hot on long up hill runs towing and noticeing not much change in cooland temp, thats where the damage will happen.

diesels

thanks again

mate if u have a reeding of 700oC from ur EGT after turbo on a 2.8 TD its not going to last long at all...... at most would be around the 600 uo a hard long hill say holds in 4th gear but even then i would be backing off the throttle..... just my 2c speaking from experience

eliteforce32 wrote:mate if u have a reeding of 700oC from ur EGT after turbo on a 2.8 TD its not going to last long at all...... at most would be around the 600 uo a hard long hill say holds in 4th gear but even then i would be backing off the throttle..... just my 2c speaking from experience

we were talking before the turbo, so after would be 500...combustion is actually closer to 1200c but that heat is absorbed in the water jackets around the motor, aswell as lost as he next charge of air comes in aswell as oil cooling from underneath the pistons.....its a balancing act...the lss heat you generate the better, but less heat means less power...so you need to set things right....assisting with larger exhaust helps, it also increases boost capability with less fuel, allows turbo to spin up fast, etc etc....
Andrew

jazza wrote:so if the exhaust gases are 700c leaving the cylinder head, and the actuall temp of the radiator coolant is 90c what is the temperature of the metal in the cylinder and exhaust manifold?
and if that super hot gases are leaving the head wouldnt any damage occure in the turbo, because the intake is getting fresh cool air every combustion stroke, or does the whole engine/every moving part heat up way too quick for the cooling system to cope and cracks occur quicker than blink of an eye and continue to grow untill a fault develops

thinking it through now, yes we want to lower egt, so big bore exhaust is on the list, expell hot gases quickly, I have noticed that my floor gets very hot on long up hill runs towing and noticeing not much change in cooland temp, thats where the damage will happen.

diesels

thanks again

The hotter things get the more they ex[pand...if the piston gets hot enough, it will grow to thesame size as the cylinder and grab it....thats why the engine maker goes out of his way to engineer a good cooling system for the combustion zone through oil and water systems. Getting the heat away and cooling it is the key...the tuurbo is seperated by oil and usually water aswell, plus cooling air running by it....the sump usually hold heaps of oil and inside the block is a heat exchanger to the coolant aswell....the cooling system is the main line of defense...because it is up front in the cool air....and can exchange alot of heat. If you climb a large mountain in the dark, and pull the bonnet up top, you will see the exhaust manifold glowing...
Andrew

One last thing....a old cow cockie once looking into my engine bay and said.....
AH A TURBO.......50% more power, 100% more problems.....and walked away.....I must say, he's onto something there....

That maybe be true, but I wouldnt have it any other way. Its turbo all the way for me Im afraid

jazza wrote:so if the exhaust gases are 700c leaving the cylinder head,

Then your pistons are resembling jelly.

Ok so what temperature in celsius would be too high, whats an extreme temp that I should not let the engine get to???

When I enquired about getting my hilux turbod just prior to xmas the three turbo shops I rang told me that the exhaust gas temp on a 2.8 diesel should not exceed 500 if I wanted my motor to last the distance. Im no mechanic and no very little about turbos but maybe this information will help you. They said they set the boost about 8psi so as not to melt anything. I didnt end up doing it as after speaking to a few people who had it done there was also issues with running hot etc even thou they fitted bigger radiators, replaced viscous fans etc and still had issues. So I decided not to go ahead with it. 3 1/2gs to have it done. Obviously yours is already done so would pay to find out what boost its running and put a EGT guage on it so you can keep an eye on the temps. Regards Steve M

I have my EGT probe on my 2.8 turbo Lux about an inch from the back of the turbo mounted in the dump pipe.
When giving it plenty of right foot on the highway I have seen temps up to 550 degrees C. I do tend to back off a bit if it is sitting in the +500 for too long though.
I will be fitting an intercooler soon so that will drop the temps a little I hope.

Yehap I fitted an intercooler off a Skyline to mine with a patrol scoop so IM thinking thats doing alot better than nothing, but I am running 9psi boost so it may of increased heat again

Ive just done the exhaust and it does go alot better, better response and alot better midrange grunt, Ive heard that some use 3inch dump and 2.5 tail section but I couldnt imagine fitting 3inch down beside the g/box and firewall so I opted for a complete 2.5inch, seeing as id never made an exhasut before, I thought I did well