Chevy 6.6 Gas Problems [4 Key Issues]

In this article, we are going to be looking at Chevy 6.6. gas problems. You will get a better appreciation of the problems you may encounter as well as how to get them fixed.

The Chevy 6.6L V8 is an engine that inspires a lot of mixed feelings from critics and owners. On paper, it looks like a great engine while in the actual controlled tests is it has failed to live up to standards.

Some would hazard to say that the engine is not at par with the options being offered by Ford and Dodge. The reason I talk about mixed feelings is that there are also owners who say that the people who are critical of it are just armchair critics who do not have experience with it in the trenches.

So, what exactly is the real story with the Chevy 6.6? Let’s dive into it.

In short, although chevy 6.6 are reliable, the common issues include engine knocking sound, lack of power and authority, weak acceleration, and weak 6-speed transmission for the engine.

Mechanic working on a car engine

Chevy 6.6 Gas Overview

The 6.6 V8 is a gas engine that Chevy introduced after the Duramax engines run on the same trucks. It came with a 6-speed automatic transmission. Traditionally gas engines are known for better acceleration.

You would expect this to be the case with the 6.6 but it is actually outperformed in this area by the Duramax engines. Here is a list of some of the problems associated with the 6.6L V8.

Chevy 6.6 Gas Problems

Knocking Sound

One of the most common complaints that have been reported is a light knocking noise that is difficult to locate but is suspected to emanate from the transmission case. It often comes up while idling in Park.

This problem has been traced down to an issue with the oil. Changing to a high-grade synthetic will solve this problem but it will take up to 1,000 miles of driving afterward for it to completely go away.

Interestingly, this is not a problem unique to Chevy engines but Ford and Dodge as well.

Lack of Power and Authority

Another complaint against the 6.6 V8 is that it simply does not pack any authority at all. The 0 to 60 time is sluggish and sometimes outperformed by the Diesel Duramax engine and is known to struggle even at 75% of towing capacity. Those who are for the 6.6 have argued that it is not a sports car engine but a truck’s and is doing what a truck engine is supposed to do.

Weak Acceleration

I’ve already touched on that but the 6.6L does not accelerate the way a gas engine is expected to which has led to numerous negative comparisons because the Duramax engine performs a lot better in this department.

This would be somewhat a cause for concern based on what you ultimately want out of your truck. There are two sides to this argument where you have those that use it as a daily driver and those who use it as a work truck. The daily driver category has issues with acceleration.

6 Speed Transmission

The other complaint is that the 6.6L engine does not have the right transmission to bring the best out of it in the 6-speed option. They argue that the 10-speed transmission would have been a better option than the 6.6/6 speed combo. Again, in this area, there are those who argue that the 10-speed transmission is too busy as it upshifts and downshifts which can create a unique set of problems as well.

What is the fuel mileage for a 6.6 gas engine?

What kind of mileage are you able to get on this engine? Well, the 6.6 V8 is capable of giving you about 14 mpg city and up to 18 mpg highway.

These figures will go lower when towing and hauling and the good thing about this is this is regular gas and not premium.

This is the argument that those for the 6.6 V8 have when comparing it to the Duramax. The Duramax needs premium diesel to get the gas mileage it is touted for.


The Chevy 6.6 is a good engine overall with some known problems. What you end up settling for in terms of engine options will largely depend on what you want to use it for.

There are many forum comments of those who love the Chevy 6.6 V8 engines even after migrating from Ford or Dodge while others have an opposing viewpoint.

Ultimately, it seems as if the dividing line is drawn at function. Those who use it for work will say that it performs as a truck should though with some limitations. Those who look at the fact that it’s a gas engine expect more in terms of acceleration as well as overall speed.

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