Blowing Bubbles
Q:
A couple of my college friends and I have started a part-time gardening/mowing business. We mostly work during summer semester, but also do some weekend work. Our goal is to make more money than we would flipping burgers and to be outside. Since we're not looking to get rich, it's pretty easy to be competitive. In order to keep costs low, we like to buy the cheapest possible pickups that are still reliable (and don't look like trash). When you're shopping the bargain bins of used trucks, engine problems are a major concern. I'm pretty good at determining the most obvious problems, but one that has surfaced a couple times is how to tell the difference between a blown head gasket and a cracked block.

Recently, we encountered this problem when checking out a super-high-mileage '85 GMC longbed pickup with (I think) a 305 small-block. It seemed to be down on power during a brief test drive. I wasn't allowed to take the truck to a mechanic, and I wouldn't anyway because of the cost. I did a compression check and the results were poor. My friend said it must be a blown head gasket or maybe worse - a cracked block. I checked for signs of oil in the radiator or coolant in the oil and didn't see any. Are there other things I can do in the field to easily check for a blown head gasket? Thanks.
Mark Harwick, Alexandria, LA

A: Oil and coolant cross-contamination is usually a good warning sign of head gasket trouble. Other problems, such as a combustion chamber leak, can vent gases right into an adjoining water jacket. One relatively simple way to check for a leaking head gasket (when obvious contamination is evident) is through the radiator overflow hose. A bad head gasket leak will pass air through the radiator overflow hose. Fill a clear jar or glass with plain water, place the overflow hose in the water, have someone run the engine, and rev it occasionally while you observe the water. A big leak will produce bubbles when the engine speed is increased. A good tool for you to get is a radiator pressure tester. This handheld tool attaches to the radiator inlet and uses a small pump to pressurize the radiator. Rev the engine with the tester attached. The dial gauge should fluctuate noticeably if there is a head gasket leak. Using a radiator pressure tester, you can pinpoint which head gasket is bad. Disconnect the spark plug wires for one cylinder head, then run the engine; it should just barely run, but enough for the test. If the test gauge still fluctuates, the bad head gasket (or other leakage problem) is in that side of the engine. If the gauge doesn't fluctuate, the problem is on the disconnected side of the engine.

If you encounter a blown head gasket when you own the truck, you may be able to salvage the situation if you act quickly. If the problem has already occurred on a truck you're considering buying, it's probably too late. Cross-contamination can harm the engine or an automatic transmission. Coolant can leak into the engine or the transmission oil cooler; oil can leak into the cooling system. If the problem is oil in the cooling system, there are flushing products that can rid the cooling system of oil. If coolant gets into the engine or transmission, the problems are more significant. Coolant can cause piston rings to stick. Water causes rust in the cylinder bores and wreaks havoc with bearings. Coolant is very bad for the clutch plates, seals, and bands of an automatic transmission.

Given the early detection scenario regarding coolant in the engine oil, you could save the engine and probably get another summer's use out of the truck. The key is to catch the problem as soon as possible. Drain the oil and flush it with chemicals made for this purpose. Of course, the bad head gasket must be replaced. If coolant gets into the transmission oil cooler, the transmission will be on borrowed time. Signs of trouble include harsh shifts and generally poor transmission performance. When you're inspecting a potential truck to purchase, check the coolant overflow reservoir and the end of the overflow tube. Any signs of a pinkish film or residue can mean coolant in the automatic transmission. Stay away from those trucks.

Milky Way
Q:
I recently bought a '95 GMC Sonoma, which was formerly used as a company truck, at a bankruptcy auction. The company used magnetic signs on both doors and the tailgate. You can tell exactly what size the signs were because there is a milky look to the paint underneath. Also, two of the signs were behind the seat and they match the bad spots in the paint. I tried waxing the affected areas and not much happened. The overall paintjob is still in quite good condition, so I don't want to repaint the truck. Is there anything else I could do to get rid of the milky areas? I hope you can help me.
Kim Osgood, via e-mail

A: We'd guess that those signs were on the truck since it was new. The combination of hot and cold cycles can lead to moisture underneath the signs. That moisture causes the milky look. You can try to remove the moisture with a heat gun. Be conservative with the heat gun; it's much easier to add heat as you go than trying to undo damage caused by excessive heat. Be aware of any plastic trim items near where the heat is being applied. Depending on the power of your heat gun, you should hold it about 4 feet from the door. Heat the paint for five minutes or less and don't let the surface temperature exceed 200 degrees. A heat lamp, such as those used by body shops, would work as well. You could also try parking the truck in direct sun so the affected area is perpendicular to the sun. If you can't exorcise the moisture, the doors may have to be repainted.

Full Flush
Q:
I'm restoring a '72 Chevy C-10 Stepside pickup that's been sitting in my dad's barn for more than 10 years. Judging by the brake fluid stains on the lower-inside parts of a couple tires, I'm pretty sure I need to rebuild or replace some wheel cylinders. I know I'll need to bleed the brake system, but I'm wondering if I should flush the whole system. What's the difference between flushing and bleeding a system? It seems like a lot of fluid goes through the brake lines whenever I bleed it. Also, is it OK to rebuild wheel cylinders, or should I just buy new ones?
Bob Tutino, Richland, WA

A: Sometimes the terms are used more or less interchangeably, but flushing a system is more thorough than bleeding. The main idea behind brake bleeding is removing any trapped air from the system. Flushing a brake system means removing all the old fluid and replacing it with new. In your case, a full flushing is in order. You might have more problems than just the leaking wheel cylinders. If the brakes were used with leaky cylinders, brake fluid can get on the brake shoes and render them useless.

We recently replaced a wheel cylinder in a similar truck that had been inactive for a much shorter period of time. There was rust and pitting inside the wheel cylinder bore; it was mostly in the areas where the seals don't make contact. Some emery cloth could be used to smooth the area, but after we priced the difference between a wheel cylinder rebuild kit and a brand-new cylinder, we went with the new part. Wheel cylinders for these trucks are very inexpensive, so it doesn't make sense to fool around with the old unit. As long as your system has been sitting and is as old as it is, you might have trouble removing the brake line fittings from the old wheel cylinders. Even when you use a flare wrench, it's still highly possible to round the nuts. If that happens, you'll have to use Vise-Grips to remove the fitting and then install new brake lines.

Six Appeal
Q:
Help! The 4.9L six-cylinder engine in my '92 Ford F-150 Flareside pickup doesn't run as smoothly as it once did. At relatively low rpms and at constant speeds, the engine often stumbles or bucks and generally runs rough. The 300ci sixer works through a four-speed manual transmission. The mileage at the time of this letter was about 150K. The problem actually seems to be worse when the truck is warmed up. Usually one would expect rough running conditions to be worse when the engine was cold, but that isn't the case with my truck. I've had some bad luck with discount gas, so I changed the fuel filter and ran several cans of fuel injector cleaner through the system. I installed new spark plug wires, a new distributor cap, and spark plugs. The plugs were pretty shot and they looked like the engine was running hot. Even so, I used the same spark plugs for replacements. I installed a new air filter, too.

All those things helped the truck run somewhat better, but the original problem hasn't completely gone away. I've invested so much time and energy in this project that I'd hate to give up now. Is there anything else I can do before throwing in the towel and taking the truck to a shop? I do have one more question. The truck is painted a metallic-magenta/purple color that must be a custom color, but I can't see any obvious signs of it being repainted. My friend John insists that it is a factory color. Do you know anything about this?
Chris Reichman, Springfield, IL

A: Try checking the intake manifold for signs of leakage. A leaky intake manifold can cause the symptoms you describe. Besides causing the engine to run rough, a leaky exhaust manifold problem can also be seen in overheated spark plugs; that can lead to the detonation-type problems that you've described. Check for any loose intake bolts; use a torque wrench to tighten them to factory specifications. While you're checking the fasteners, inspect the gasket edges for signs of carbon deposits. A leaking gasket can allow carbon to escape, and you'll see this evidence on the part of the gasket that's exposed. If the gasket looks questionable, replace it. It wouldn't hurt to try the next-colder spark plug. Engines that have an air pump emission control system make sure that the anti-backfire valve isn't stuck in the "open" position.

Regarding the color of your truck, it's hard to tell from a letter, but given the year and the fact that your truck is a Flareside, our long-distance guess is that you have a color called Iris. Ford introduced it as a way to make the Flareside stand out from the crowd. You can check if the paint is original by looking at a data plate. A paint supplier should be able to decode the paint code. You can also look around and under the edges of the weather stripping to check for evidence of paint buildup from a repaint or different-colored paint.

Dim Bulb
Q:
I have a hard time seeing the gear selector display at night in my '99 Tahoe. This only happens when I have the headlights on. I don't think the bulb is totally burned out, so what else could be the problem?
Brad Harris, via e-mail

A: Try adjusting the dimmer control switch. Lots of pre-'00 GM trucks have experienced this problem, but fortunately, the solution is about as simple as it gets. If you need added details, such as how to properly grip the dimmer switch and how much torque to apply with your wrist, you can check GM technical service bulletin 99-08-42-009.