COOLING SYSTEM SERVICE

Transcription

1 26 August 2007

2 WHAT S NEW IN COOLING SYSTEM SERVICE BY PAUL WEISSLER Today s cramped engine compartments make cooling system leak detection anything but routine. Knowing how and when to look for leaks can be every bit as important as knowing where to look. At one time, tracing a cooling system leak was a pretty straightforward operation you often could see the coolant stain. And if you couldn t see it, pressurizing the system and looking around after the pressure gauge reading started to drop usually would help pinpoint the location. In the tougher cases, using trace dye was the clincher. Not any more. Today s packed engine compartments with the beauty, silencing and underbody covers mean you have to remove lots of components just to have a fighting chance to see where even an obvious leak is coming from. Sure, if it s a General Motors V6, those technicians who focus on pattern failures are going to make assumptions. But there are a lot of good replacement gaskets for intake manifold leaks out there now, both original Montage art: Harold A. Perry; photos: Jupiter Images and Wieck Media August

3 Pressure-testing the cooling system usually will identify most leaks. Look carefully if you spot coolant, though, because so many hoses and gasket joints are close together in today s tight engine bays. A couple of dozen hose connections in a vehicle s cooling system is hardly an unusual sight for today s technicians. This pressurized coolant reservoir alone (arrow) has three hose connections all potential leak locations. Photos: Paul Weissler If a leak doesn t show up during a simple visual inspection, installing trace dye in the system and looking around with an infrared black light normally will help. This leak from a radiator header gasket is a common type, but may require removing plastic covers and panels to be seen. equipment and aftermarket. As a result, the number of unrepaired leaks caused by the OE gaskets has slowed to a trickle. The leaking manifold gaskets did teach many technicians an important lesson: A lot of leaks can occur with the engine off and cooling down, and before the system is warmed up and fully pressurized. You ve got to be ready to look for leaks at any number of different times and operating temperatures, and check the engine oil for the milky look that signifies an internal leak. There just isn t any shortcut on this issue, even for the more common external leak. There can be two dozen or more cooling system connections and gasketed joints. And there s no guarantee that even with the covers removed, you can see all of them. But with the covers in place, there s no chance. If you don t take your time removing the covers, you ll have grief when you try to put them back. You can replace some plastic fasteners with universal Christmas trees, but if you leave out one or two because your assortment doesn t have a couple of the right sizes, there could be rattles and, with underbody covers, physical damage that could lead to overheating. All the cooling system connections are there for good reason more heat exchangers. There are coolers for engine oil, transmission oil, power steering fluid, some EGR systems and turbochargers both the air-to-water intercoolers and the bearing housings. And in the cases of the Toyota, Ford and GM hybrids, there are second cooling systems with auxiliary electric water pumps for the electronics. Coolant also flows through the throttle body and intake manifold. As the overall layouts get more complex, it often takes a second, electric water pump on nonhybrids just to get adequate coolant flow at idle and part throttle. In fact, three water pumps including two Photo courtesy Tracer Products 28 August 2007

4 Reservoir Tank The intercooler on a turbocharged engine (like this Subaru opposed 4-cylinder) not only adds coolant hose connections but a second fill cap as well, on the engine. auxiliary electrics are being used on late-model Prius and Camry hybrids. Add in the need to physically package the water pump and all the heat exchangers, and creating the flow circuits that route the coolant in the proper proportions and in the right sequence to all the locations, including a possible split Engine Coolant Temperature Sensor Water Valve Coolant Heat Storage Tank Outlet Temperature Sensor To Heater Core in flow between cylinder heads and block and you can see that finding cooling system leaks is no walk in the park. Depending on the vehicle, even the engine-driven pump may be relocated to the flywheel end. Some Cadillac Northstar V8s and Ford Duratec V6s have that setup. From Heater Core Dedicated Radiator The Prius also has three water pumps. In this case, the one for the heater circuit also supplies hot coolant to a Thermos-bottle type storage tank, where it stays warm for up to three days. When the engine is started, coolant flows from the tank to the intake manifold to reduce the engine s cold-start emissions and improve cold driveability. Water Pump The new hybrid Toyota Camry has three water pumps one engine-driven, one for the heating system and a third (the one shown here), which cools the hybrid-related electronics by pumping coolant through a dedicated radiator atop the standard radiator. Water Pump For Heater Coolant Heat Storage Tank Coolant flow through the intake manifold and throttle body, and the resulting need to seal some difficult joints, has made intake gasket replacement a common repair for coolant leakage, even beyond the GM V6s. You have to learn to follow cooling system layouts, which have begun to look almost as complex as a wiring diagram. Before you can even find a leak, you have to understand interrelated coolant hose circuits that may involve more than two dozen connections, many of which are out of sight. If you can read a cooling system layout diagram, which are often complex, that s one way to start. Some companies, such as Nissan, Ford and Chrysler, provide coolant flow diagrams. Toyota has them under New Car Features on the factory website ( but you may have to refer to the model year in which the vehicle of that generation was introduced. Even if there s no flow diagram, there may be a good illustration of the entire cooling system, so you can see where all the connections are made. Honda provides this type of illustration. General Motors provides simply a written description of its systems, but even that can be helpful because it covers the coolant flow paths. However, if you want to see all the hose connections, about all you can do is refer to Illustrations courtesy University of Toyota 30 August 2007

5 Rear-mounting the engine-driven water pump, as on this Ford 3.0L Duratec V6, allows it to be packaged in a tight engine compartment. However, it makes the coolant circuit and leak detection more complex. This diagram illustrates coolant flow through a late-model Nissan Altima 2.5L four-cylinder engine. The circuit has both a conventional thermostat and what s called a water control valve actually a second stat. It blocks coolant flow through the block until coolant temperature is 200 to 206 F; the conventional thermostat opens at 177 to 182 F. Illustration courtesy Nissan Thermostat Radiator Oil Cooler the individual replacement procedures for hoses, heat exchangers and components. The combination of the written description with the individual replacement procedures, however, should give you a useful picture of the system. Most leaks occur when the cooling system is under pressure. But the highest pressures actually occur within the closed-thermostat loop during warmup. When the stat is closed, those internal system pressures get very high. In some engines they exceed 75 psi, many times the rating of the open-stat cooling loop. The gaskets also have to seal against the effects of thermocycling, and although modern gaskets have good resilience, eventually they do take a compression set. So if a sealing gasket leaks, it s no surprise. In fact, Thermostat Thermostat Water Pump Heater Heater Valve This Toyota 4.7L V8 diagram shows that the coolant circuit includes an engine oil cooler and coolant flow to the throttle body, with a second stat at the inlet. Illustration courtesy University of Toyota gaskets have a tough time anywhere they have to seal against coolant leakage, but they do pretty well overall. You ve got to be prepared to look everywhere, from hoses to water pump, radiator and heater circuits, even at engine core plugs. As we go through the diagnostics, you also should notice that deteriorated coolant is a frequent root cause of leakage, and any leak repair should include a thorough flushing of the system, not just a radiator drain. That s for the do-ityourself crowd, not professionals. Hoses Hoses still are probably the No. 1 source of leaks, but why? Well, they not only thermocycle, but they carry hot coolant at pressure as well. If the coolant has deteriorated, it can be conductive, and the current causes internal damage to the hose. Hoses also are exposed to underhood heat, cold winter temperatures, ambient air pollution, road splash and, in some cases, engine oil. In short, its operating environment isn t friendly. The deterioration is visible in the form of surface cracking from underhood heat and ambient ozone. Hose clamp joints used to be a big issue, because of the compression set hose takes under the clamp. But with 32 August 2007

6 constant-tension clamps, that has moved down the problem list. Instead, we have the O-ring sealed joints, typically at the heater necks, but also at other locations, including some radiators. The joints are made with push-on quick-connects, which take the guesswork out of whether or not a sealed connection was made. However, now we re relying on a plastic fitting Quick connectors for the heater hoses, with an O-ring seal instead of clamps on the hose necks, make it easier for the workers on the assembly line. But if they have to be removed for service, it s tough work in tight quarters. with an O-ring in some cases, and one that must survive thermocycling, pressure, debris, voltage attacks, etc. What you do depends on where the leak is coming from. If it s from the O- ring seal, you can release the plastic quick-connect (often not easy, particularly if the heater necks are in tight quarters). Then you have to get the right replacement O-rings, often from These quick connectors are for the heater hoses at the engine, where access is easier. The arrow points to the replaceable O-ring. O-ring seals have been used even at the radiator end, as this upper hose joint shows. The clamp in this case is a shrink-band type. the dealer. Very important: Make sure the heater neck is in good condition, cleaning off any debris with a lightly abrasive cloth. The headaches come when the hose is the problem. There are all kinds of repairs you can make, of course, including splicing in a repair section. But unless there s good reason you can t (such as part unavailability), replace the complete hose assembly. If you can simply disconnect the leaking hose and push on the new hose, fine. If the old hose fitting is stuck, you have to be really careful getting it off. Don t pull or pry with pliers or you could damage the neck. You can use a small rotary grinder to cut the fitting along its length, then unpeel it. But any use of force that damages the heater neck, or going too far with the grinder and nicking the raised stop of the neck, can leave you with a major leak that won t seal. Then you ll really be into a jury-rig repair, including the possibility of having a radiator shop install a new neck. It s worth taking the extra time, and removing whatever you can to improve access, to avoid running into a nightmare. If you can t get a new hose but can get the old one off, you should be able to install a conventional heater hose and a good clamp. Lubing the hose and neck with antifreeze makes it a lot easier to install and locate the hose. Position the clamp against the outer edge of the raised stop. In very tight quarters, you can first just slip on a plastic bandtype clamp on the hose end, then use a heat gun to shrink it for a tight fit. Radiators and Heaters Why do radiators develop leaks? Yes, there are older vehicles and lowerpriced aftermarket radiators, with soldered-together copper-brass that suffer pressure- and corrosion-caused leaks at the header joints and tube perforation from worn-out coolant. But most of the on-the-road fleet is aluminum with plastic tanks, and the failures tend to be leakage at the gasket joints, and stress and thermal cracks in the tanks. We do sometimes see failure from electrolysis, which produces voids in tubes, but for the most part, it s pressure and temperature, with some vibration from deteri- 34 August 2007

7 orated mounts thrown in, that are the culprits. Pressure can cause a leak at a bad cap, but often it s just a high-normal peak and the effects of thermocycling. If it s an expensive radiator that s in otherwise good shape, you can have a radiator shop replace the header gasket. Don t just recrimp. If temperature is causing a leak, perhaps with a low coolant level causing steam erosion damage to the tanks, you can consider the cost-value equation between a new complete radiator or having a radiator shop replace tanks and gaskets. But don t overlook the coolant issue: Flush the system and fill it really fill it which means use a machine. Most radiators are so-called shakers that is, they serve as mass that absorbs engine idle vibration forces. However, the rubber mounts have to be in These heater hose quick-connects are crimped onto the hose. If they re stuck and you have to cut through the crimps to be able to peel them off, you can use a grinder. But be careful not to nick the heater core necks. good condition, and because the lowers may be regularly bathed in road film, they should be inspected when a radiator suffers leakage. Heater cores are prone to the same problems as radiators, plus a number of others as well. Although plugging is No. 1, leakage is a solid No. 2. The leading cause is bad coolant, and occasionally electrolysis creeps in. In either case, a flush & refill is an effective part of the cure. But when the failure occurs after a hose replacement, the cause may be erosion from a high coolant flow rate, where the technician perhaps didn t realize the original hose had a flow restrictor. Both radiators and heater cores may suffer leakage from core sand in the coolant. The cooling passages are washed at the factory, but core sand still remains and erodes holes in the tubes. It happens a lot less than it used to, but never say never. We ve heard plenty of war stories about heaters that fail repeatedly. But did they occur with the necessary flow 36 August 2007 Circle #24

8 restrictors in place, and with thoroughly flushed cooling systems? You might even be able to put some of the blame for these failures on substandard parts. But we do recall more than one heater core that was found not to be leaking after factory testing. The real cause was a hose connection that allowed coolant seepage through the firewall. If you can t find a coolant leak in all the usual locations, check the coolant reservoir. Leakage from plastic seams and the bottom hose connections is surprisingly common. Adding a dye trace to the cooling system nailed this one. Water Pumps and Reservoirs Water pumps leak, and with today s recessed pumps, particularly with transverse engines that make pump inspection and replacement tough, it s usually a hope-not. A pressure test usually identifies a large pump leak, whether from the gasket or the shaft seal, but you shouldn t just assume that a few drops on the ground under the pump is a tip-off. Every water pump weeps coolant past even a normal seal; there are even weep holes to allow it. In fact, you can buy clip-on wick assemblies that absorb weepage and allow it to evaporate, for your Nervous Nellie customers. Photo courtesy Tracer Products If the plastic reservoir is out in the open, you often can find a seam leak on a visual inspection, even a trace dye line. However, the complete reservoir isn t always in plain sight; in fact, you may have to remove some trim to get a look, which may show that it s a nicked hose that s actually producing the leak. Although sealer can help stop minor tube leaks in the radiator and heater, don t try to use it as a cure-all. And don t overdose. You may end up stopping the leak, but at the cost of plugging the radiator and/or heater, and we all know what new symptoms either of those problems can cause. Visit to download a free copy of this article. 38 August 2007 Circle #26