Brrrrr... Humbug J W h o t u r n e d o f f t h e h e a t? ust as few people can tolerate poor A/C performance in summer, there aren't many that can accept lack of heat in winter. No matter what part of the country your shop is located in, there has got to be some time of the year when your customers need a little heat in their cars. Hey, it even gets pretty cold at night in the southwest. We know there are some cars that are tougher to heat than others. There are a variety of reasons why this happens. Perhaps it s borderline coolant flow rates through the heater core. Or if the engine radiates a lot of heat, the BTUs may go flying from the aluminum block and heads to the great outdoors when the ambient temperature drops. Many Japanese transverse-fours fall into the second category, particularly Hondas. But if you really filled the cooling system at the last service, and it hasn t sucked in a lot of air since, it should be able to keep a reasonable person comfortable, if not absolutely toasty warm. When we talked about overheating last summer, we said we d bring back the subject of a full cooling system again this winter, and so we are. An engine that s short on coolant not only will be prone to overheat in summer, but there won t be a solid column of hot coolant flowing through the heater to transfer enough heat in winter a real double whammy. Bleed Baby Bleed, Or Flush And Fill Okay, you believe that you have to really fill a cooling system, and you re tired of all the tricky airbleed steps and repeated thermo-cycling of the system. Frankly, we ve never seen anyone who could drain the system on such cars as VW vans, Nissan Sentras, 1989-90 Maximas, or Toyota MR-2s, and get a good refill with any consistency. These cars may be among the toughest to fill, but the problem is hardly unique. Help for tough bleeding problems is available, and it only costs money. A drain and fill machine that fills the system with fresh coolant as it pulls the old coolant out, does the best job we ve seen. Does it get every last drop? No, but it s probably good for an average of 95 percent, which beats pulling frozen drain plugs and going through an elaborate fill procedure. The two leading machines are the Wynn s Powerflush and the Robinair ProFlush & Fill. These machines use adapters to connect to the upper radiator hose. If you re in an area where coolant recycling is legally required, you can get a combo machine like the Wynn s Du-All, or just collect the coolant from the flushing machine in drums, and ship it off-site. (Photo 1) 8 December 1997
A flush-andfill machine is a lot faster and easier than trying to fill, bleed, and thermo-cycle a cooling system. Air bleed plugs may be anywhere. This one is on the radiator, because the pressure cap is not. 2 1 Check coolant temperature with a scan tool or as shown, with a pyrometer. If coolant temperature is down in the 120 s, you won t get acceptable heater performance. 4 3 A rubber seal around the valve provides a positive coolant shutoff in many thermostats. If the engine radiates a lot of heat, this may be one of the items used to help maintain coolant temperature in winter. What if you don t have a machine and you do have a heating problem? Just remember all we ve said before about opening all the air bleeds not all of them are on the engine. We ve seen them in coolant hoses, even on the top of the radiator where the cap is on a pressurized reservoir or the engine (Photo 2). And jack up the front of that engine compartment way up. You almost can t jack it high enough before you start refilling the system. In fact, on the Maximas, you have to jack up the front absolutely as high as possible (bottom of the bumper more than three feet off the ground), and don t be surprised if the tailpipe touches the shop floor. Then run the engine at fast idle for about a half hour after filling the cooling system, to purge the entrapped air, waiting until you see nothing more than some tiny bubbles at the fill neck. Mmmm. A flush-and-fill machine does sound tempting, doesn t it? Coolant Temperature There are cars with heating systems that won t satisfy a dogsled driver, unless you block the front of the radiator with cardboard. But realistically, you can t expect much heat from the heater if the coolant temperature is down in the 120 degree range (Photo 3), so check the coolant temperature. If the temperature at the coolant temperature sensor (checked with a scan tool) or at the upper radiator hose (checked with a pyrometer probe) is over 180 degrees F, there should be adequate heat, even in really frigid weather. If the system once delivered adequate heat, but doesn t now, and the coolant temperature is clearly below specs, it s worth checking the thermostat. A lot of stats will seep enough coolant at low temperatures to weaken heater performance on those borderline heating cars. A stat with a positive seal, such as a rubber ring, may help (Photo 4). December 1997 9
Brrrrr... Humbug The heater coolant valve has to open fully for good heater performance in cold weather. On this older Volkswagen, the heater output is directly related to the heater coolant valve opening. 5 Make sure the radiator electric fan is off if the coolant temperature is low. A radiator shop friend of ours went through a laundry list of checks and suddenly it dawned on him: the cooling fan was running. In that case it was a blown fuse on a Mazda with a normally-closed fan relay (designed to protect the system from overheating in summer). We ve also heard of similar problems caused by a stuck relay or a bad temperature switch. Also watch for any not-socreative rewiring of a fan circuit that may have been done during the summer, in an attempt to lower the high-side A/C pressures on a car with a condenser that is coated with road film. If you re using an infra-red (non-contact) thermometer aimed at a heater inlet hose, measure close to the engine to get the best possible reading. Even then, expect the reading to be as much as 15-20 degrees F lower than coolant heading for the radiator. If you happen to hit the heater outlet hose at the firewall, the reading might be much lower. The infra-red thermometer is a good tool with which to measure temperature drops, and that s what you should use it for. Example: if the system has a heater coolant valve, check the inlet and outlet temperature at the valve with the dashboard lever in full hot. If there s a drop of more than a few degrees, the valve apparently isn t opening fully. If it s a vacuum-operated valve and it responds to disconnecting and reconnecting the vacuum hose, remove the valve and try flushing it out, or install a new one. Temperature Cable Adjustments Most imports have cable-controlled heater coolant valves. Check to see if the valve opens all the way by operating the valve s external arm. If it doesn t, disconnect the cable housing from its retainer, put both the dashboard temperature lever and the valve arm in the full COLD or full HOT position, and snap the housing back into the retainer. Then recheck, and make sure the dashboard control fully opens and closes the heater valve. All VWs but the late models With the cable housing disconnected, move the heater valve arm to the fully-closed position (and the dashboard temp control to COLD) or vice versa (arm to open and dashboard control to HOT). 6 control heater output by regulating the flow of hot coolant through that valve, so its adjustment is the key to effective heater operation. (Photos 5 and 6). This adjustment may not do the job if the cable is connected to the temperature door in the HVAC (heat-vent-a/c) case, because the problem may be the adjustment of the cable from the dashboard control panel to the temperature door. So if there s just one cable from the dashboard control panel, it goes to the temp door. And apparently there s a cable from the temp door to the heater coolant valve. That s okay, because if the heater coolant valve isn t opening all the way, the temp door cable adjustment apparently is out of adjustment. So the temp door isn t moving to full heat position either. In fact, an incorrectly adjusted cable to the temp door is one of the most common causes of poor heater performance. Sure, some Japanese cars have joined the rest of the world and switched to an electric motor-controlled temp door operation and a dashboard potentiometer. Electric motor-controlled temp doors are usually part of an Automatic Temperature Control system, but there are a lot of cable setups in manual A/C cars. Honda just switched to a temp door motor on the 98 Accord, but Civics, even Camrys and the new Sienna minivan still 10 December 1997
Honda Accord temperature door cable control is typical of Japanese cars. Disengage the cable housing, move the door arm and the dashboard control to the same position (try Hot in Winter), and snap the housing back into its retainer. Clamp Control Arm Figure 1 Control Cable have a temperature cable. On some cars you can hear the cable-controlled flap door hit its stop when you operate the dashboard temperature control hard against its COLD or HOT positions. If you can t, you ll have to dig into the dash (often just dropping the glovebox and an underdash trim piece) to reach it. Before you adjust anything, make sure the temperature door moves freely from open to closed. If it doesn t, that s a problem to be fixed first. Plastic parts occasionally become distorted due to the temperature cycles they must endure. The adjustment is basically the same as the one at the heater valve (Figure 1). Because A/C cooling in summer is considered more critical, manufacturers generally specify putting the temp control in COLD, the flap door arm in COLD, then snapping the cable housing back into position. However, if you re in a frigid area, you can use the HOT positions instead, and perhaps pick up a couple of degrees F. at the floor outlets. If you have to readjust the temp door cable adjustment, also readjust the cable at the heater valve. Some cars still have the socalled self-adjusting clip at the end of the temperature cable. If the heater coolant temperature is hot and the flow through the core is good, and the temp door itself isn t binding, a clip adjustment is a reasonable thing to try. Move the temperature control to COLD, hold the temperature door arm in the full COLD position, and pull the cable wire through the selfadjusting clip until there s about 3/4-inch between the end of the clip and the stop at the end of the cable. Then operate the temperature control to make sure the temperature door moves to full HOT. The Heater Itself Heater cores on many latemodel vehicles are often dogs to replace. The instrument panels are part of the safety structure of the car, and the car has to pass a crash test, so... You really want to be absolutely sure a heater core is plugged or leaking before you replace it... absolutely, positively sure. Unfortunately, we re seeing many more plugged cores these days because it s expensive to replace a leaking radiator or heater. If someone thinks there s a coolant leak anywhere, they pour in a jug of stop-leak. Maybe they pour in two jugs. If they think the leak has subsided but hasn t stopped, they may pour in a third jug. Or they just pour it in as preventive maintenance. Heater core tubes are much smaller in diameter than radiator tubes, so guess where all that stop-leak accumulates? The best way to check is to clamp off the heater hoses, disconnect them and attach auxiliary hoses to the December 1997
Brrrrr... Humbug 7Check coolant flow through the heater or back-flush the heater core to remove stopleak and other debris. One way is to attach auxiliary hoses as shown, aim one down from the fender and open the water valve to the other hose. If you don t get a solid stream (in the forward direction), the core probably is plugged. Reverse the hose connections to back-flush. 8 Look at the hose necks to see if they re damaged or corroded, as these obviously are. They can allow a coolant leak that may lead you to suspect a leaking heater core. PHOTO COURTESY OF NATIONAL AUTOMOTIVE RADIATOR SERVICE ASSOCIATION (NARSA). 9 The Lexus LS400 is one example of a vehicle with detachable tubenecks, sealed by O-rings and clamps. The design improves serviceability, but if one joint ever leaks, installing a new O-ring and clamp is not a quickie repair. A Leaking Core heater core necks. Then connect a water hose and run water through the heater. If the flow is weak and you see any fibrous particles coming out, that s a sign of a plugged core. As long as you have the hoses connected, attach the water hose to the outlet and back-flush the core (Photo 7). No significant improvement? Before you give up, reconnect the heater hoses, pour a heavy-duty flush into the cooling system and let it circulate. Then try to flush it again. When you have good flow through the heater, you re ready to do a drain-and-fill and the heater performance should be much better. Heater cores do corrode and leak, and when they do, you ve got to replace them. Over the years there have been HVAC case designs with easy-access covers to the heater. Unfortunately, that s doesn t always mean a super-quick job. The Lexus LS400 has an access cover, but the job still is factory flat-rated at over 4-1/2 hours. But just think of how long it might take without the design. The Infiniti Q45 and BMW 7 series are factory flat-rated at about an hour more, and the Mercedes E-class at over six hours more. Of course, it took a heater core design with detachable tube-necks to permit the slide-out design (Photo 8). 12 December 1997
Brrrrr... Humbug 10 This is a premium hose clamp for tough-sealing situations. The coil spring compensates for any compression set in the heater hose. Also note the narrow band inside the clamp. It spans the joint of the clamp, providing 360-degree clamping force. PHOTO COURTESY NARSA. And it s possible that what s leaking is an O-ring seal, or a clamped joint for a tube-neck. In some cases, the leak actually is at the hose connection, and the last thing in the world you d want to do is go through a heater core replacement for that. You re absolutely sure you d never miss a hose connection leak? Well, it s a lot easier than you think because the foam seal often protrudes to the engine compartment side of the cowl, and coolant seeping from the hose connection flows into and through the foam seal, into the HVAC case and leaks through a joint in the case to the passenger compartment floor. Disconnect the hoses and look at the necks. If they re damaged or corroded enough to prevent a great seal (Photo 9), it s really worth checking the heater with a pressure test. If you want to do heater work, you absolutely need the kinds of adapters that permit you to plug off one heater neck and apply up to about 20-25 p.s.i. to the other, then shut off the pump and see if the pressure holds for 2-3 minutes. There are adapters for this purpose that work with cooling system pressure testers, so they re not a big investment. But when you make this test, be sure the adapters are connected so they really seal on the hose necks, or the pressure won t hold. If the problem is seepage at a hose connection, an ordinary hose clamp may not be enough. One choice is the new heat-shrink plastic clamp from Gates Rubber. It shrink-tightens to conform even to a damaged neck with just a minute or two from a heat gun or a hair dryer. This clamp continually self-tightens to compensate for any compression set in the hose. If the quarters are tight, the shrink band can be difficult to remove without hose damage, however, so an alternate choice is a constant-tension clamp. You tighten it, compressing a spring too, and the spring compensates for any compression set in the hose, so clamping force is not lost. One of the better designs is by Oetiker, as it includes an internal band that spans the joint of the clamp, to provide 360-degree clamping force (Photo 10). And Don t Forget... When you re trying to figure out the cause of poor heat, here are a couple of things to remember: Cold air may be escaping through leaking joints in the HVAC case. While many American car companies weld their plastic cases to reduce the number of joints, most Japanese cases are still segmented. This improves serviceability, and with good quality control, they should be fine. But if there s leakage at a case joint before the heater core, the air that flows out is cold. Another source of cold air leaks can be a hole in the cowl. One of those cowl foam seals may be dislodged, perhaps due to something that was done during summer A/C service. Did you check the floor air temperature on both sides of the car? The typical system is biased to provide a bit more warmth to the feet of the driver, because he or she is assumed to have bought the car. So if you find the air temperature is adequate (135 degrees F. or higher) at the passenger s side, and much lower at the driver s side, there s a ductwork problem, or perhaps a cold air leak. Most people put off preventive maintenance during the winter. As long as the car starts, runs and stops, they want to keep going, right past your shop. But if you can warm their feet on a cold winter day, they ll stop in. By Paul Weissler 14 December 1997
EXHAUST SYSTEM BUZZ Some 1994-96 Honda Accord four cylinder models may exhibit a buzzing noise at 1800 RPM while accelerating at part throttle. This noise may be heard in cars equipped with either manual or automatic transmissions. The same vehicle may also produce a groan or droning noise at 2000-2400 RPM. These noises have two distinct causes. The 1800 RPM buzz sounds like a vibrating sheet metal piece, and is most common in cars with manual transmissions (although it can also occur in cars with automatic transmissions). It can be reproduced most reliably by upshifting from first to second gear at a low speed (so the engine speed is approximately 1200 RPM) and applying heavy throttle. The noise can be heard as the engine passes through the 1800-2000 RPM range. It can t be reproduced by holding the engine at 1800 RPM in neutral or any other gear. Countermeasure parts are available to correct this condition. The 2000 RPM groaning noise is most common in cars with automatic transmissions. It can be reproduced by driving the car in D3 or D4 in the 2000-2400 RPM range with a steady throttle. It is most noticeable when driving up a slight grade or in stop-and-go traffic. More sensitive owners may also feel a slight vibration in the steering wheel, accelerator pedal, or floorpan. The countermeasure parts and procedures described in this bulletin will have very little effect on this noise. Any noises in the 1800-2400 RPM range that remain after installation of the countermeasure parts kit should be considered characteristic of the vehicle. Other possible causes of these noises include bent or misaligned exhaust system components. Diagnose this by examining the rubber exhaust system hangers. A problem is indicated by one or more of these being twisted. Correct this by loosening all the bolts in the exhaust system so the system can seek its own neutral point. Then retighten the bolts. Installation of the countermeasure kit involves replacement of the gaskets at both ends of the mid-pipe. To replace the gaskets: Remove the four bolts mounting the mid-pipe to the catalytic converter and exhaust pipe A. Note: Some models have a heated oxygen sensor mounted in the mid-pipe. Do not damage it while doing this repair. GOOD BAD Remove and discard the old gaskets. Install the new gaskets. Reinstall the mid-pipe to the catalytic converter and exhaust pipe A with the new bolts, nuts, and springs in the kit. Torque all four nuts to 22 Nm (16 ft-lb). Examine the exhaust pipe hangers, and make sure they are sitting vertically (refer to illustration above). The exhaust mid-pipe fastener kit (Honda P/N 18010-SV4-305) contains two gaskets, four flange bolts, four springs, and four selflocking nuts. Information for Dealer Direct is provided courtesy of the ALL- DATA Corporation. December 1997