noob needs help with mileage - only 10 MPG!
cyl %
1 35%
2 30%
3 25%
4 25%
5 34%
6 25%
I know these are not good, but do they explain the poor mileage?
Are there specific things I should be asking my mechanic to look at?
rmchrgr,
The car doesn't run rough, but idles rough once it warms up. It idles fine from a cold start.
Yes!
When there is electricity, I am a tech at a dealership. I do powertrain exclusively. When a customer comes in and complains their car is running rough at any point, it
usually means a misfire. We have the benefit of a scan tool to tell us which cylinder is missing but on your car, your guy will have to rely on older technology and/or experience for diagnosis.
Anyway, The first step we usually take with this scenario is to swap coil/plug to another cylinder to see if the miss moves. Since you have one coil, he might do a plug. If the miss does not move with the plug, it can be ruled out as faulty.
So if the plug is OK, the next step is usually a leak down test. In our shop, again, anything over 20% will warrant an engine tear down. At least the head would be coming off to check the valves/seats/springs etc. 35% leak down represents a very large combustion leak. Something, whether it be a valve, head gasket or whatever is not sealing during the combustion process and is allowing excess fuel/air mixture to not be properly burned.
Does he have a chemical type combustion leak tester that goes over the radiator opening? Probably. If it has a head gasket leak, have him show you the color change with the car running.
Could be a simple vacuum leak, Does the condition go away or get worse when you put it in gear?
It is odd that the car runs OK when cold and idles rough when warm, usually its the opposite as parts warm up. Usually that type of situation gets worse over time if the condition is not corrected.
Regardless, the drivability does not explain the large leak down numbers. I'd say that your mechanic probably does not want to deal with taking the head off a car that he might be stuck with for a while before he can find whatever parts he needs. Taking the head off would be no problem but if he finds bad valves, bad seats, springs or whatever, he will need to find parts somewhere. Then it's at least a head rebuild/reman which ain't gonna be cheap.
If I had to guess, your guy is gonna need to get pretty far into it to solve your issues. Unfortunately, he really can't give you a definitive answer until the head comes off though. I guess I'd speak to him about what's involved with that and whether he wants to do it. If he does take the job on, I'd get a written estimate and make sure he either shows you what he finds and/or leaves the worn parts for you to inspect.
We often run in to this with people at work. They have an older, high mileage car that's been neglected for a while and exhibits some mechanical problem. Unless they have a warranty, we usually ask for several hours labor time up front to take it apart and make sure we diagnose it right. It's not always possible to know exactly what the problem is until you see it. Often they decline because the cost to repair is more than what the car is worth.
I'd think about doing this yourself. Do you have the space/tools/time? Most gear head types are gonna want to do this at some point, sort of a right of passage. Is that you? Would be a good way to learn. Or maybe just find a better running Slant and drop it in for now while you rebuild the one in your car. There's probably someone near you yanking one out for a V8.
Bottom line, you need to figure out why you have 35% leak down and where it's coming from whether it be exhaust/intake/head gasket/rings. If you have to pay your guy an hour to tell you, then that's what you have to do.
I could be way off base here though, hard to diagnose a car over the internet. Maybe post a video of how it runs?
