Exactly which model Sentra do you have? If you have an SER or Spec-V, then you may be in luck. Nissan had issues with the Altima engines that were also used in the SER and Spec-V Sentra’s and they have a secret factory warrantee. If you have another model with the 1.8 or 2.0 engine, then you’re out of luck for that.
I agree with some of the others that your mechanic isn’t doing a thorough job of analyzing the issue. When he pulled the plug and found liquid in the cylinder, he should have taken a sample of the liquid with a Q-tip and stuck it in some clean water. If an oil slick formed on top of the water and/or water beaded up on the Q-tip when it was removed, then that would be gasoline. If the water mixed with the fluid on the Q-tip, that would be antifreeze. He could have also smelled the Q-tip to detect gasoline.
A few seconds of further testing could have saved you a lot of money. It is also possible, not likely but possible that you had two problems and now you only have one.
I finally got around to pull out the spark plugs and check the cylinders for myself. I pulled #1 and #4 in order for comparison. Here’s a picture of the plugs with #1 on the left and #4 on the right.
I did not see any liquid in either cylinders, although, I could only see straight down with my flashlight. However, the bottom of cylinder #1 looked very clean while the bottom of cylinder #4 looked like it has a coating or film of some kind on it that was a little shiny.
Also, my coolant level went from slightly above max to below max since I topped it off 2 - 2 1/2 weeks ago, probably ~100-200 mL total.
Once again, get a Q-tip and stick it into the cylinder and swab the top of the #4 piston, then stick the Q-tip in a glass of water. If there is the slightest bit of gas in it, it will form a sheen on top of the water.
Don’t swab too hard as there might be some oil on top of the cylinder, just dab the top of the piston. This needs to be done as soon as the plug is removed as the gas will evaporate quickly. So put the plugs back in, run the engine through a drive cycle (fully warmed up), shut down and let sit overnight or at least until cooled down. Then remove the #4 plug and dab the piston top.
Yeah, I will do the q-tip check, I just need head to a pharmacy to get the extra long ones. I don’t think I have anything that can reach far enough into the cylinder. I will post once I can get a sample from inside the cylinder.
@keith - I finally got around to checking the liquid (I was away for a few days). Yesterday I drove to/from work and parked in the garage. This morning I pulled the plug from #4, and there was definitely a lot of liquid in it. It’s hard to say, but maybe ~a few millimeters deep. I put some yarn on the end of a wooden dowel (couldn’t find the long Q-tips) and soaked up some of the liquid. When I swished around in some water it seemed to mix right in and there was no sheen on the surface. It also did not have a gasoline smell, more like exhaust fumes. It was also not as slick feeling as engine oil, which I tested just by pulling the dip stick and getting some oil on my fingers.
All that being said it seems to me (as a non-expert) that it’s coolant in the cylinder and not gasoline or engine oil.
@GeorgeSanJose - I didn’t check the gap, but the plugs only have a few thousand miles on them so I don’t know if I would expect to see that kind of wear yet. Maybe I would given the way my car starts sometimes though.
Just goes to show the importance of good basic diagnostic skills. The original mechanic who diagnosed gas in the cylinder could easily have checked the fluid to find out whether it was coolant or gas. Maybe he did sample the fluid and just got it wrong. But it shouldn’t have been difficult to diagnose correctly.
Great news. Just for my own curiosity, what is the difference in the repairs necessary between gasoline in the cylinder versus coolant? Should I expect the cost to come down from the initial estimate when they thought it might be gasoline? When I take this to the mechanic, should I just say that I tested the liquid and think its coolant?
If it was gasoline, a new injector would be the fix.
Unfortunately, since it is coolant, the fix is a new head gasket. This means the top of the engine has to be removed, and it is much more expensive than just replacing an injector. Yes, tell the mechanic you found coolant in the cylinder. You might want to shop around for quotes on the head gasket since you want someone competent and reasonable in price.
I think it is possible on some engines for coolant to enter the cylinders via a defective intake manifold gasket too. That wouldn’t be as expensive to repair as a head gasket problem. Mechanics have tests which will differentiate between the two. Best of luck.
I agree with @GeorgeSanJose. Coolant could be getting in through the intake, either by a bad gasket or a flaw. I’d put some UV dye in the coolant so that the leak track can be easily recognized as parts are being disassembled.
So here is what I hope is my final update. I had my car at the mechanic this past week to repair the head gasket. They found that the head was slightly warped, maybe from a previous over heating, and the head gasket was “burned” in between cylinders 3 and 4. Though, he said there wasn’t really a “smoking gun” in terms of an obvious leak point. Now only time will tell if the problem is solved.
Thank you everyone who posted. It was helpful, and I learned more about engines than I thought I would ever know. Hopefully this thread is dead.
