Automania/Repair & Maintenance

AUTO QUESTIONS AND ANSWERS FOR WEEK 19

by Bob Hagin

Q. I recently overhauled my 4.0 liter Ford Explorer engine and replaced the cylinder heads. My problem is that the temperature gauge is fluctuating back and forward from "C" (cold) to "H" (hot). I have had the radiator boiled out, installed a new temperature sending unit, water pump, cooling fan clutch, and radiator cap. But supposedly the engine is not running hot. When I tore the engine down, it had a full pan gasket under the intake manifold but now it only has a two piece gasket in its place. I don't know if the original was a heat shield or not. W.J. Windsor, NC

A. If the original reason for your overhaul was overheating and engine failure, it's possible that the temperature gauge unit itself suffered damage. The first order of business is to determine if your Ford's engine is actually having those temperature gyrations or if the gauge is faulty. The best way to do this is to substitute a "master" mechanical gauge in place of the temperature sending unit and drive the vehicle a while with the gauge temporarily mounted under the hood. If this gauge acts normally, your problem is electrical, so you won't have to pursue the possibility that you did something wrong when you went through the engine. I can't imagine how the different manifold gasket could cause the problem unless it is lacking coolant passage openings that were present in the original. It's always best to hold a new gasket up to the old one to make sure the openings line up.

Q. My 1996 Jeep Grand Cherokee exploded (yes, with a loud bang) in my driveway early one morning and the engine compartment burst into flames. No one was in the car and it hadn't been touched, moved or driven for at least eight hours. The fire department says it was probably the battery that exploded. I find this hard to believe as I would expect a spark would be needed to trigger an explosion and flames. Is there a history of Jeeps exploding? How can I find out? What could have caused the explosion? I am afraid of continued electrical problems if it is repaired. Would a complete replacement of the vehicle be my best approach? The vehicle is still under warranty. F.J. Pittsburg, CA

A. Several different brands of vehicles have been known to burst into flames after being parked for a relatively long period of time. In most cases, the cause has been traced to batteries that had built up internal pressure caused by the breakdown of the water in the electrolyte into oxygen and hydrogen. The spark was provided by the battery coming apart and creating a spark when the terminals blew off the cases. The likelihood of the problem reoccurring is remote unless the replacement battery suffers the same malfunction. You can trace this problem through the internet and it should also be reported to the National Highway Traffic Safety Administration by calling 1-800-424-9393.

Q. I am shopping for a heavy-duty pickup to pull a 24-foot travel trailer for general use. I wanted one with a diesel engine because I have heard that it is not unusual to get as much as 300,000 miles from trucks with diesel engines. On a recent visit to a car lot, a used car salesman told me that I could count on getting 700,000 miles out of a diesel engine. This sounded unrealistic to me. What is the average mileage one can expect to get from a diesel engine? M.G. Mountlake Terrace, WA

A. Engine longevity isn't the selling point of a diesel. Fuel economy and pulling power are more important to most diesel pickup buyers. If you're an average driver and put around 15,000 miles on your vehicle per year, your purchase would be 33 years old after just 500,000 miles. Other stuff like the transmission, running gear, etc., would wear out long before the engine and besides that, you might be tired of the truck by 2032.