DIAGNOSING COOLING SYSTEM WOES: DO IT NOW. You ve got a vehicle in your bay whose engine is BY PAUL WEISSLER

Size: px

Start display at page:

Download "DIAGNOSING COOLING SYSTEM WOES: DO IT NOW. You ve got a vehicle in your bay whose engine is BY PAUL WEISSLER"

Kathlyn Tate
5 years ago
Views:

1 DIAGNOSING COOLING There s a large buildup of rusty powder on the cap of this radiator on a 4.3L V6 in a three-year-old GM van. Mileage was only about a third of the 150,000-mile service limit, but the coolant level was low. The radiator fill neck doesn t look any better. Although the rest of the system might live after a good backflushing, replacing both the radiator and fill cap probably is the safest approach. SYSTEM WOES: DO IT NOW BY PAUL WEISSLER A neglected cooling system doesn t read the calendar, so there s no right time of the year when it comes to cooling system service. Warn your customers: Postpone service now and you ll regret it when the seasons change. You ve got a vehicle in your bay whose engine is running hot, maybe even has overheated. The motorist wants a diagnosis, but perhaps only to see if he has to get the repair now or can safely postpone it. In his mind, the approach of fall with lower ambient temperatures may lead him to believe his problems are over until next summer. However, some of the root causes for hot engine temperatures also can be responsible for lack of heat in the cold weather. In addition, some of the basic reasons for unsatisfactory passenger compartment a/c cooling in summer can 28 August 2002 Photo: Paul Weissler

2 August

Weight Valve Spring Valve Vacuum Valve Spring Valve Spring Valve Lower Sealing Gasket Vacuum Valve Lower Sealing Gasket Vacuum Valve Here s a side-by-side comparison of the weighted valve-type

3 Weight Valve Spring Valve Vacuum Valve Spring Valve Spring Valve Lower Sealing Gasket Vacuum Valve Lower Sealing Gasket Vacuum Valve Here s a side-by-side comparison of the weighted valve-type radiator cap (left) vs. the spring-loaded vacuum valve. The spring-loaded vacuum valve is closed until drawn open by vacuum developed in the cooling system as hot coolant cools down. The weighted vacuum valve is open (allowing debris to accumulate) until pushed closed by coolant expanding under pressure. When enough debris accumulates, the valve does not seal even when pushed closed, so coolant flows out into reservoir, even overflowing the reservoir and resulting in a low coolant level. lead to inadequate warmth in winter. So the problem you fix now also can deliver benefits in the cold months to come. Anything that reduces coolant flow in summer can raise coolant temperatures and possibly cause overheating. That s straightforward. In winter, low coolant flow combines with some reduction in coolant temperature (from low ambients and heat loss from the radiator and engine block) to produce a heater problem, even when coolant temperature itself isn t low. Here s why: You can t just look at actual temperatures. A half-gallon of coolant at 220 F contains a lot less heat energy (in BTUs) than two gallons of coolant at 160 F. If some problem keeps coolant temperature relatively high but significantly reduces coolant flow through the heater, the heater can t transfer as much heat to the passenger cabin in the same amount of time. Approximate numbers, if we assume a half-gallon of coolant per minute is flowing through the heater at 220 F vs. two gallons at 160 F: 850 BTUs every minute for the half-gallon of 220 F coolant BTUs every minute for the two gallons of 160 F coolant about three times as much heat energy available to warm the cabin. Here are the service problems that may have two or more causes: Restricted Cooling System What can restrict a vehicle s cooling system? There are many causes, but the two we see most often are rust and corrosion and sealer in the system. Electrolysis is also a big contributor to restricted coolant flow. Rust and corrosion. In case you thought that everything is made of aluminum and won t rust, take note of the fact that trucks and SUVs are half the market, and those engines usually have cast-iron blocks at least even the Toyota V8. With poor cooling system maintenance, you can believe the reddish-brown stuff forms. Sure, the extended-life coolants usually carry a 5/150 or 5/100 change interval. However, poor maintenance is not just failure to change the coolant on a time-based schedule. Even worse is allowing the cooling system to run with a low coolant level, which allows air into the system. That creates a great breeding ground for rust, and there s no more severe example than GM s 4.3L V6. The photo on pages is not a one-ina-million case. This is a frequent problem, at a fraction of the 5- year/150,000-mile recommended service interval for DexCool. The OAT (organic acid technology) coolants are in wide use and gaining in OE usage. However, I can t say I m a big fan of wholly-oat antifreezes such as DexCool, which seem to be overly sensitive to low coolant level (among other things). However, in the GM 4.3 V6, the root cause for low coolant level at low mileage, without a leak, is a weighted vacuum valve in the radiator pressure cap. A factory fix to forestall the problem is a cap with a spring-loaded valve. The longtime OE weighted valve is open until closed by buildup of cooling system pressure. Before that occurs, some debris in the system can be deposited on the upper side of the valve. Over time, the buildup is enough to keep the valve from sealing closed when the pressure builds. Coolant flows out of the radiator into the overflow reservoir, which itself eventually overflows, causing loss of coolant. The replacement cap deals with that problem, but cleaning out the rust powder buildup in the system is something else. There s a GM bulletin on the possible use of a heavy-duty cooling system cleaner, which is a specific 30 August 2002

The end tank was removed to reveal the white solder corrosion that covers the ends of the radiator tubes in this copper/brass radiator that was assembled with high-lead solder.

Of course, you can t just install the right cap on a plugged system and expect good results.

4 The end tank was removed to reveal the white solder corrosion that covers the ends of the radiator tubes in this copper/brass radiator that was assembled with high-lead solder. The result is restricted coolant flow. two-step product oxalic acid and neutralizer. It s not easy to use properly, and if you make a mistake, don t say we didn t warn you. Of course, you can t just install the right cap on a plugged system and expect good results. One possible approach is to backflush with a full-feature flush & fill machine first the heater core and then the engine block (thermostat removed because of the debris issue). Replace the radiator, then If you suspect the system is plugged with sealer or other debris, check for restrictions in lines, hoses, heater and radiator with an infrared thermometer. If the readings are not reasonable for the coolant temperature and location, backflush the entire cooling system with a flush & fill machine. Photos: Paul Weissler really fill the cooling system (a good flush & fill machine also is key to success in this area) and warn the motorist to keep the system topped up and to have the cooling system checked once a year. GM continues to endorse DexCool for this engine (and all others except its new Pontiac Vibe, which is Toyota-engineered). However, some shops point out they never saw these problems with conventional American green/gold (silicated) antifreeze. So if you agree with that line of thinking, you may be more comfortable with installing a green/gold antifreeze with silicates in cast-iron block engines. Green/gold may require a shorter service interval, but the motorist who encounters the rusting problem should be ready to shorten maintenance/inspection intervals anyway. Just because a system won t rust because it s almost all-aluminum (including the engine block and heater core), doesn t mean it can t suffer from corrosion. Aluminum corrosion particles can be carried to the radiator, where they may be deposited and plug the tubes. Also remember that not all radiators are aluminum. Many OE and aftermarket radiators in vehicles currently on the road (particularly heavy-duty units) are copper/brass radiators assembled with high-lead solder. This solder is prone to solder bloom, corrosion deposits that block the radiator tubes. Sealer in the system. Cooling system sealer has been shown to be a useful product. In fact, it was called the great Band-Aid for the Cadillac V8s of the 1980s, in which it stopped coldengine coolant leaks. However, lately it s been used for preventive maintenance, a practice instituted at GM plants. GM reengineered its cooling systems to prevent leaks, but kept the sealer in use as a security blanket in a few plants. Well, GM finally stopped all sealer usage on the assembly line over two years ago, and so should you. Sealer should be used only to actually stop leaks, and only when the customer can t go for replacing the leaking part. Don t install more than a single dose of sealer. It can and will plug the narrow passages of some radiators and in heater cores. Excessive use of sealer 32 August 2002

5 creates real problems, and engines that had a factory-installed dose obviously would be prone to this if more sealer was added later. Many coolant flow passages in the engine are anything but wide highways. A buildup of excessive sealer can slow or deflect the coolant flow through the engine. If this happens in an area where combustion raises metal temperatures to levels where high coolant flow is essential for proper cooling... Well, how about engine knock, head gasket burn-through or even melting of metal? If the customer is the offender, he may tell you how much sealer he s put in, if you take a careful vehicle history. If the source of the problem was a series of shops just looking to get the vehicle out the door, you ll have to do some major investigating. Some sealer particles generally accumulate in the reservoir, particularly the pressurized type. Because GM used sealer on the assembly line for so many years, it is particularly aware of this problem. It reports gelatinous deposits of a color that may resemble rust, but actually is sealer buildup, plus some debris from hose degradation. The problem has been most common on the 60 V6 (both 3.1L and 3.4L pushrod engines) and the 3800 V6. Electrolysis. MOTOR readers have read our discussions of electrolysis as a cause of corrosion and hose internal degradation, producing debris that can restrict a cooling system. We won t repeat them here, but you can get a refresher at (most recently with the Trouble Shooter column in the September 2001 issue). Checking for Restrictions When sealer buildup or rust/corrosion accumulations result in overheating, you may find the restrictions lead When checking for combustion gas bubbles in coolant with a gas analyzer probe (engine idling, cap off), cover the fill neck with plastic wrap and hold it in place. Make a slit in the plastic and push the probe through, just into the open neck. To avoid damage to your gas analyzer, keep the probe tip out of the coolant. to uneven heat transfer. So if you take temperature checks all over the cooling system with an infrared thermometer, you may get unexpected readings. We can t tell you specifically what might turn up, but you ll know when readings don t make sense, such as a hot engine, but only 110 coolant at the inlet heater hose, or a big temperature drop along a hose or coolant metal line. We can t provide a rule-of-thumb spec for temperature drops across the heater hose necks because the numbers vary so greatly according to vehicle model, ambient and coolant temperatures, antifreeze concentration, blower speed, etc. However, you re usually likely to see a drop of up to 20 to 40 F, so if the inlet hose neck is close to engine coolant temperature and the outlet neck is much, much lower perhaps close to ambient temperature a plugged core is pretty likely if heater output is poor. To check things further, you can disconnect the heater hoses and attach auxiliary hoses and a water hose to the inlet. If there s just a trickle from the outlet, that makes the problem pretty apparent. The radiator may not be plugged enough to resist a good backflush, but a heater core just might be beyond cleaning. If you can t get a solid column of water to flow through a heater core, replace it. Low Coolant Level, Concentration The rusting problem with GM s 4.3 V6 really involved both low coolant and a restricted system. Although other engines don t end up with the rust accumulation, they also may suffer from overheating in summer and poor heater output in winter. One major cause is an improper fill or a system with some of the space taken by combustion gases leaking across the head gasket. Not every system loaded with air or gas bubbles is self-bleeding, and even if it is, the self-bleeding may be far slower than the entry of the bubbles. If you see bubbling when you open air bleeds, that pretty well confirms the issue. You can identify gas with a combustion leak detector in the coolant fill neck (or cover the fill neck with clear plastic wrap and push through the probe of a gas analyzer, just into the neck opening, out of the coolant). If you find combustion gas bubbles, you ll have to identify the source (such as head gasket or other leak) and eliminate it, or you ll en- August

Air bleeds can be anywhere on the cooling system. In this vehicle, the red plug in the radiator hose is an air bleed. Photo: Paul Weissler counter the same problem down the road.

6 Air bleeds can be anywhere on the cooling system. In this vehicle, the red plug in the radiator hose is an air bleed. Photo: Paul Weissler counter the same problem down the road. Air and gas pockets are tough to eliminate unless you use a premium drain & fill machine or take the time to do the job manually, opening all the coolant air bleeds. Some techs think there are just one or two air bleeds on an engine, but these bleeds also may be built into a hose (including radiator and heater hoses). Not all air bleeds, particularly on an engine, are in plain sight, so check your CD- ROM information system. As for low coolant concentration, a mix is what everyone recommends, and although there s some margin in that (45-55), when the antifreeze percentage gets down to the 15% to 20% level, the system may be more prone to corrosion than with 100% water. So if the system has been topped up with water periodically, check the percentage with a refractometer or hydrometer. A test strip is not as reliable an indicator, and even less so now with all the different antifreeze dyes out there. Weak Water Pump A deeply recessed water pump can take half a day to replace, so a wornout pump is not good news. Why would a pump wear out so it doesn t pump as much coolant as it should? The primary reason is called cavitation erosion/corrosion the sudden formation and collapse of bubbles in the coolant as the pump draws in and then compresses the coolant. As the bubbles collapse, they implode, hammering the surface of the water pump chamber, eroding the anticorrosion protective layer of the antifreeze. Some water pumps are more prone to cavitation than others. The silicatetype corrosion inhibitors in conventional green/gold antifreeze work very quickly to reapply a protective layer before corrosion can eat away the chamber and reduce pump performance. Silicates work much faster than OATs, so Chrysler s new longlife antifreeze is a so-called hybrid. Based on a formula originally used by Mercedes in both diesels and gas engine vehicles, the hybrid contains just enough silicate inhibitors to provide primary protection and fast repair to the protective layer in water pump chambers, and some organic acids (and other inhibitors) for extended service life. The hybrid antifreeze is similar to what Ford is phasing into its U.S. products, although it has other reasons, too. (An organic acid inhibitor used in many wholly-oat products seems to affect gaskets in the Ford V8s.) So you can look for a third type of antifreeze on the market. Valvoline, affiliated with the European company that already sells a hybrid for use on the Continent, has just started marketing this 34 August 2002

You can also see pockmarks near the edges of the impeller blades. This was a two-year test run over 100,000 miles. third type now.

7 Cavitation Erosion, Corrosion of Pump Chamber This water pump from a Dodge van with a 5.9L V8 running with a wholly-organic-acid coolant suffered severe pockmarking of the chamber after a road test in the Colorado mountains. The result was cavitation erosion, followed by corrosion. You can also see pockmarks near the edges of the impeller blades. This was a two-year test run over 100,000 miles. third type now. It s called Zerex Extreme G-05, and a similar formula also is available from the car dealers here if you want to go that route. Tracing a problem to a weak water pump isn t easy, because a plugged radiator may reduce coolant flow to produce similar hot-run symptoms. The difference is that a restricted radiator is more likely to be responsible for higher coolant temperatures in highway operation than a weak This water pump is from another vehicle in the same Colorado test. It used a hybrid fluid (low-silicate antifreeze similar to Mercedes coolant) and obviously fared much better. There s no evidence of cavitation erosion or corrosion. Photos courtesy Valvoline pump. And you often can test or inspect a radiator in less time than it takes to pull and check a water pump. Auxiliary electric water pumps are coming into wider use (both as original equipment and as factory-fix retrofit devices), and if they fail, they might be responsible for both overheating in summer and poor heat output in winter. It depends on the computer strategy, because the basic objective in all cases is to increase coolant flow. If an electric pump is triggered by a cylinder head metal temperature sensor, as on the Lincoln LS and Jaguar V8s, a pump failure can cause the engine to run too hot. If a pump is intended to improve heater output in low-speed coldweather operation, as on 2000 GM minivans and 2001-on Dodge Durangos, it comes on in low ambient temperatures. Only if the electric pump is controlled for both situations can it cause double trouble if it fails. Air Leaks An engine may not be running hot, but you still can be facing the same root cause for poor a/c cooling in summer and inadequate cabin warmth in winter. The real issue may be neither coolant flow nor the refrigeration system; rather, it may be a matter of airflow. Okay, you know about the temperature control door or the heater coolant control valve, and you check those as a routine item. However, outside air leaks just don t get respect as a source of the problem. Yet they allow hot ambient air to leak into the cabin during the summer and cold ambient air to enter during the winter. Bad seals around the door openings, between the HVAC case and the cowl and even around the fresh air intake may be responsible. Now that you ve got them in mind, get them in the crosshairs of your diagnostic sights. Visit to download a free copy of this article. Copies are also available by sending $3 for each copy to: Fulfillment Dept., MOTOR Magazine, 5600 Crooks Rd., Troy, MI August 2002

In the old days, if a cooling system COOLING SYSTEM SERVICE UPDATE

In the old days, if a cooling system COOLING SYSTEM SERVICE UPDATE 20 August 2005 COOLING SYSTEM SERVICE UPDATE BY PAUL WEISSLER There s no sense longing for the good old days. Today s cooling system service requires specialized equipment, an understanding of coolant/antifreeze