2015 Silverado with 5.3 gas in oil

HauserHooch · November 27, 2022

Hey there, I'm not sure where to go from here. So I changed my oil and noticed there was a significant amount of gas in the oil. About a 1.5-2qts.

Called about the only mechanic in my area I trust, who has his own shop. He changed out the high pressure fuel pump with gm parts. Fast forward a couple months later (don't drive it much anymore) oil level is again high on the dip stick so I changed it, smells like gas about 1qt high. Take it back, tells me he thinks I got a bad high pressure fuel pump again, puts in another new one (again factory parts), doesn't charge me a cent this time. Assures me that was the problem and I must have got a bad one from the factory.

Well the oil level is up again and smells like gas again.

Keep in mind, the truck has ran fine, has thrown zero codes, though the argument could be made my fuel economy seems to have tanked, though I don't do as much highway driving as when I first purchased it new in 2015, so I can't say for sure. Averaging about 15.5 when before I was around 19+.

I do have a local Chevrolet/Gm shop in town, yet due to past issues with them telling me my air filter is dirty and needs to be replaced and my wiper blades are worn and need to be replaced approximately one week after I installed a new K&N filter and brand new wiper blades. I can't in good faith go to them for a fix.

If anyone else has had similar issues and found the root of the problem please let me know!

CamGTP · November 27, 2022

A leaking fuel injector could also be a cause.

Grumpy Bear · November 27, 2022

As could be a leaking hard line fitting if they are not being replaced or properly tightened.

customboss · November 27, 2022

Over-serviced K&N out of the plastic factory bag can cause oil wetting of MAF and contribute to fuels dilution after said oil cooks to heated MAF. That would not put 20+% fuel in oil.

Windshield wipers sure will ruin an engine......LOL

You have an internal fuel leak and if we are SURE the fuel pump and associated plumbing isn't leaking then injector/s are suspect.

Let us know what corrects the issue.

KARNUT · November 27, 2022

9 minutes ago, customboss said:

Over-serviced K&N out of the plastic factory bag can cause oil wetting of MAF and contribute to fuels dilution after said oil cooks to heated MAF. That would not put 20+% fuel in oil.

Windshield wipers sure will ruin an engine......LOL

You have an internal fuel leak and if we are SURE the fuel pump and associated plumbing isn't leaking then injector/s are suspect.

Let us know what corrects the issue.

Damn, I must’ve been just plain lucky again. Or as Derrick on vice grip garage says I pretended I didn’t see that. As many oil bath filters I’ve used over the years K&N and Amsoil. I’m guilty of over oiling. If I had over fueling in the oil. Amsoil probably saved me again.

movario · November 27, 2022

I had the same problem with my 2014 5.3. Not the high oil level, but smell of unburnt fuel and high fuel consumption. Oil smelled like fuel.

I replaced all the injectors, and since then, everything is fine. A defective high pressure fuel pump would cause at least an check engine light, and would cause the engine running lean, not rich.

A faulty injector can leak and cause this issue without causing a check engine light.

Other probable causes for an engine running too rich are:

- Defective coolant temp sensor --> Is the engine temperature within plausible levels?

- Defective Thermostat --> Are you getting the engine to operating temperature? Especially on highway speeds?

- Defective O2 Sensor --> Depending on the mls you may replace them anyways, as they age.

- Defective MAF Sensor --> Already mentioned

- Heavy short distance driving

But most certainly i'd suspect the fuel injectors.

I wouldn't recommend driving like this for too long, as the fuel washes away the oil film on your cylinders and may cause additional wear.

Grumpy Bear · November 28, 2022

On 11/27/2022 at 12:34 PM, movario said:

A defective high pressure fuel pump would cause at least a check engine light, and would cause the engine running lean, not rich.

In my recent experience, it will never see a light with the high pump leaking. At least to 8% fuel dilution. O2 sensor feed back just drives the duty cycle up until the lean condition is solved or you run out of capacity. Trims fall in line really fast. Just did this with lab results on oil/fuel. It is insane how much it can be off and not throw a code.

customboss · November 28, 2022

18 minutes ago, Grumpy Bear said:

In my recent experience, it will never see a light with the high pump leaking. At least to 8% fuel dilution. O2 sensor feed back just drives the duty cycle up until the lean condition is solved or you run out of capacity. Trims fall in line really fast. Just did this with lab results on oil/fuel. It is insane how much it can be off and not throw a code.

Absolutely true, MIL codes are designed to control tailpipe and vapor emissions.....NOT OPTIMIZED engine operation.

movario · November 29, 2022

8 hours ago, Grumpy Bear said:

In my recent experience, it will never see a light with the high pump leaking. At least to 8% fuel dilution. O2 sensor feed back just drives the duty cycle up until the lean condition is solved or you run out of capacity. Trims fall in line really fast. Just did this with lab results on oil/fuel. It is insane how much it can be off and not throw a code.

Ah yes sure. I was talking about the pressure being to low on the fuel pump (due to wear). I totally forgot that these pumps can leak into the engine. You are right, the pump leaking into the engine (and the fuel pressure still being ok) would not cause a check engine light.