EGT and petrol engines

[Henk_B]

I have this question that I would like to find an answer for.

EGT is used ver good in Diesel Engines, so that one can see spikes in temp etc, so that one can save the engine. That much I know.

I have read that EGT can be use in petrol engines, but since petrol engines are controlled by butterfly, you get a place where the temp would peak (that would be the optimal place for the engine to work),
Colder temps mean that 1)more petrol, which is unburned (which is cooling down the cylinder) or 2) running lean.

Do I understand it correctly, and if so, then an EGT is not that essential in a petrol engine?

Many thanks

[ChrisF]

uhm ja ...

standard vs modified ....


On a standard petrol engine EGT is virtually a constant, and falls inside the design parameters. Thus no gauge needed.


Modified .. uhm ja ... what type of modification ?

- Chip - bit more fuel, but really should not push up the temperature too much.

- after market bumpers, spot leghts etc - THIS is the primary cause of high WATER temperatures for petrol engines, NOT high EGT values. We have slotted and drilled massive holes into many aftermarket bumpers to get the airflow sorted again.

- engine swop - when doing an engine change you really need to pay attention to the cooling system and air flow and radiator size and .... However, these are NOT EGT related.


Thus EGT related issues are not the norm with petrol engines. The engine will run "rich" and cause other issues before the EGT becomes an issue - on a PETROL engine.


at least that is my understanding of it ...

[ThysdJ]

It has got to do with the way diesel fuel burns versus the way petrol burns. Petrol gives a quick burn, and diesel burns very slowly. That is one reason why petrol engines rev higher than diesels.

That also means at high revs, the diesel does not get time to fully combust inside the cylinder on the power stroke and the gasses are still burning during the exhaust stroke and by the time they exit the exhaust valve into the exhaust manifold. This is what causes very high EGT. Using an EGT guage to monitor the EGT's will tell you when you are busy overcooking it a bit, so that you can reign in the horses for a while until things cool down a little.

I suppose you could put an EGT guage on a petrol engine, it can do no harm..

[Thabogrobler]

On a turbo petrol engine more petrol is added to the combustion mix to lower the EGT's - thus the opposite effect than on diesels.