My truck is an '85 Chevy C10 shortbed stepside with a 305ci engine and an automatic transmission. It runs OK, but it doesn't like to stop running. It keeps running even after I turn off the key. The problem is especially bad in hot weather. It knocks and rattles. It sounds like the engine is on its last leg. I've found that if I turn off the key while the transmission is still in Drive that the engine stops. What causes this problem and how can I fix it?
Carbureted engines like yours are susceptible to engine run-on or dieseling, especially in hot weather. The engine tries to keep running even after the ignition is turned off because of heat buildup in one or more cylinders. Fuel injected engines don't have this problem. Common causes of dieseling are too high idle speed, too lean air/fuel ratios (often caused by vacuum leaks), and excessive carbon buildup in the combustion chambers. You should check your idle speed and adjust it if necessary. Carbureted engines commonly have an anti-dieseling solenoid. You could have a defective solenoid. There are chemical additives and sprays that are supposed to help eliminate carbon buildup. If these products don't do the job, the cylinders' heads will need to be removed for a thorough cleaning. Dieseling is hard on an engine, so you're doing the right thing by turning off the ignition while still in Drive, but stopped. You can also try using Premium grade gasoline.
GMC vs. Chevy, Thick vs. Thin
I want to buy a late-model sport truck, preferably a 2000-or-later GM product. Until recently, I didn't care which one, but my uncle was shopping for a new truck and the salesman at the GMC dealership told him that GMC tolerances are closer and GMC gets the best parts, while Chevy gets the leftovers. The salesman claimed to be a former machinist, so he knew stuff like that. I've never heard about any quality differences between GMC and Chevy trucks. Is what the salesman said true? If so, does that hold for all years of GM trucks? My concern is mostly about rust. This same salesman also said that the thickest frames and body parts go on GMC trucks. If this were so, I would think that I would have a better chance of avoiding rust-out problems with a GMC.
You've heard of urban myths-well, this is a salesman's myth. The salesman must have thought your uncle was a real pigeon. GMC and Chevy trucks are built on the same assembly line by the same workers using the same parts. Except for trim items, emblems, grilles, and different model equipment packages, the two trucks are identical. Can you imagine the extra trouble and expense it would take to measure every part and separate them by degree of conformity to specifications? And what about the class action lawsuit when Chevy truck owners found out they got thinner fenders than GMC owners? This imaginative sales pitch reminds us of the very old myth that Sixties and Seventies GMC trucks were tougher than Chevys because of their association with GMC commercial trucks. Any connection between 1/2-ton GMC pickups and 2-ton-plus trucks was strictly advertising hyperbole. If you're really concerned about future rust problems on a 5- or 6-year-old used truck, consider buying a truck from outside the rust belt. With all the online auto- and truck-buying sites, you can find West Coast and Southwest trucks quite easily. We have a Michigan friend who regularly finds pristine rust-free trucks and cars (on eBay and Autotrader.com) on the West Coast and takes them back to Detroit. He figures it costs about a thousand dollars to get the vehicle home either via transporter or by getting a discount airline ticket and driving home. Our friend always recoups his travel expenses when it comes time to resell the West Coast trucks.