Originally Posted by
Blknight.aus
rough rules for EGT if you have ally pistons (yes you do) and a pre turbo EGT sensor
in driver speak.
600 is 0k
650 is when you want to be thinking "maybe I should be gearing down"
700 is when you should be thinking "I should have geared down"
750 is when you should be thinking "why havent I geared down?"
800 is when your mechanic is going to be unfriendly at you and use words like, butcher, inept and "why'd you bother to install a pyro if you weren't going to pay attention to it?" your repair bill will probably get spiked just to teach you a lesson about your lack of vehicle sympathy.
in mechanic speak
600 is survivable, your not doing any undue damage or increasing your wear but you are technically pushing the engine so your fuel economy is out the window in favour of more torque. your engine can do this forever but the fuel tank wont like you.
650 is still survivable but you are not winning any friends in the wear and tear department, if you have preexisting faults in pistons, heads, valve seats or your cooling system pushing to here will start to expose them. in theory the engine can do this forever but your wallet will let you know about it by way of the bowser
700 is not good, very short term exposures to these temps are survivable BUT, the combustion temperature at the point of maximum combustion chamber pressure is above what aluminium can deal with long term, once all the allys heated up its going to start going west unless your engines ability to shed heat through the pistons underside oil cooling is good (which it is in a td5). the oil that is being splashed up onto the underside of the pistons will be breaking down. you can maintain this for maybe a minute
750 is very not good everything that was happening at 700 will be happening here but faster. combustion pressure and temps can be high enough to start eroding the piston lands and skirts where the fire burns down past the gaps in the rings. The heat being applied to the top of the piston is now getting towards the limit of conductivity of the metal (think of holding an ally can in your hand, you can melt the bottom off with an oxy torch without the top of the can getting hot enough to burn your hand) you are turning your oil into carbon based grinding paste on the underside of the pistons. you can do this for maybe 10 seconds and thats assuming your engines perfect, dont forget that in getting to this temp youve had to spend time at 700+ so you have less time at this temp if its been a long slow increase as opposed to a sudden increase. If its a sudden increase you need to ask why.
800 ahh yes sir, youve turned your pistons all insideoutsidemelty its time to rebuild.
for a post turbo EGT sensor drop all those numbers by about 100 degrees or more depending on how far post turbo you gauge is and how quick its reaction is.
