We've all had that stomach-dropping feeling. You know, the one that comes after realizing the engine-temp gauge is in the red-or worse, the feeling that follows when the radiator or overflow tank boiling over from running way too hot.
"The Trip That Never Was" (Nov. '06) was the first indication there was a problem in the cooling system in Trasborg's M-715. Two boil-over overheats and two stops because the gauge was pegged were the indicators. The truck was built during a New Jersey winter and was driven 400 miles in the next year and a half leading up to that trip. In the following year, we learned and relearned more ins and outs of engine cooling than we want to ever again.
Somewhere along the line, we decided all the little things done to the truck (and some we'd done in the past) would make a good story if we stuck them all together.
Look, we aren't gonna spoon-feed you exactly how to fix your Jeep's overheating problems. What we're gonna do is use Trasborg's truck as a canvas and paint a picture of many (if not all) of the typical Jeep enthusiast's cooling-system woes. Use it as a guide the next time your Jeep is running hot and you are 140 miles from home.
Whenever the water pump comes...
Whenever the water pump comes off, if there is even the slightest doubt in our mind about the condition of the pump, we put a high-flow one in its place. (In this case, the M-715 got a Flow Kooler.) In addition to moving more water, the high-flow units are just flat-out more reliable and built better than most parts store junk.
Throughout this thing, we...
Throughout this thing, we kept hearing people say, "Bet your head gasket is bad." Well, we had no oil in the coolant and no coolant in the oil-we weren't losing any of either. Apparently, you can have a problem and not have leakage or loss. Often, it will show itself in the form of combustion gas in the coolant. This Block Tester from NAPA (PN 7001006) effectively sniffs the coolant to see if you have internal head or head gasket problems.
If you've swapped radiator...
If you've swapped radiator hoses, did you swap the wire too? That wire, which most of us hate, is really a necessary evil. The feed hose (opposite the return hose from the engine) can collapse from suction at higher rpm if there is no spring or wire in it. You'll need to go junkyard fishing if you don't have one. We have made them out of coat hangers in the past in a pinch.
If you've already got electric...
If you've already got electric fans and an automatic controller, make sure the fans are coming on when they're supposed to. Toggle your A/C switch or manual override to see if that helps the overheating, or just watch the gauge while idling and see if the fans turn themselves on when the temp comes up.
Then came the water-pump issue....
Then came the water-pump issue. We've pulled pumps off Jeeps that had no impeller vanes left. With no idea when the last water pump was put in this engine, we pulled it to check. The impeller vanes were OK, but there was some play in the shaft.
File this under "things we...
File this under "things we never would've thought of without the truck overheating": The 1-inch (or larger) gap between the radiator and the core support can allow air to flow up and around the radiator. The gap was so big that we could drop a screwdriver and it would fall to the ground. When we put the radiator in, we were just worried about the metal destroying the radiator with vibrations.
Cappa convinced us to move...
Cappa convinced us to move the sending unit away from the headers for a more accurate reading to the temperature gauge. Before you go monkeying with the sending unit location, if you've got a single-wire unit, put a potentiometer in line with the sender, then turn the knob. With the key in the on position, turning the knob should move your gauge. If it doesn't, your gauge is bad. If it does, you can figure out the resistance at a particular temperature and check the gauge manufacturer or factory service manual to see if it's operating correctly.
We fixed that problem with...
We fixed that problem with some cut-up fenderwell liners from our YJ. We didn't see a huge difference in this one, but keep it in mind when swapping non-OE radiators into your Jeep.