Pumps, jackets and heat exchangers

Jan. 1, 2020
A wise vehicle owner will recognize the axiom that a dime’s worth of prevention is worth a hundred dollars worth of cure.

What we do in this business is keep America rolling by maintaining transportation resources, and our job is to repair or to prevent concerns. Without automobile technicians, everything that travels on the world’s highways eventually would grind or rattle to a halt, and civilization would come to an end. Vehicles provide so much that we take for granted, including personal freedom. Imagine yourself without an operable set of wheels to get my point.

Sometimes a simple peek under the radiator cap will be grounds for a flush job.

When it comes to maintaining those rides, a wise vehicle owner will recognize the axiom that a dime’s worth of prevention is worth a hundred dollars worth of cure, and nowhere is that more pertinent than in the water jackets and heat exchangers of a car’s powerplant. While most customers think regularly about their oil, coolant condition typically is forgotten until the temperature gauge swings too far to the high side or rusty stuff begins to paint underhood parts and find its way to the pavement.

The challenge of educating customers is more demanding every year. Many owners are fairly savvy, but there are others I’ve encountered who don’t even know what model year their vehicle is, let alone whether it has a four cylinder or a V6. They usually can tell me it’s a Chevy, a Nissan or a Dodge, and that it’s a pickup or a sedan, but very little beyond that.  The point is that if these folks don’t know their vehicle any better than what I’ve just described, they aren’t likely to understand the importance of cooling system maintenance until they’ve experienced steamy side-of-the-road trouble that leads to a large repair bill. Some of them simply wait until their car is exhibiting symptoms before having anything done, and that leads to disaster.

This is about as bad as it gets. This Toyota Camry drove up to one of service bays having burst this particular hose only a few hundred yards up the road. The person driving the car decided on the fly to wheel in when the hose popped and steam erupted from the edges of the hood.

The cooling system on my 2007 F150 calls for a 17.6-quart mix of the gold stuff and distilled water to be replaced at 100,000 miles. With the coolant flush machine my department owns, it was quite easy to shove new coolant in, displacing the old. That works if the system is clean, but without adding a flushing chemical, the machine doesn’t do such a good job on a system that’s clouded with rust. On those I shove a lot of water through before displacing that with coolant mix. On my own truck, replacing the coolant at 100,000 miles almost seemed wasteful, because the coolant I shoved out looked just as good as the coolant I was shoving in, but I did it anyway. 

The clock had reached the change point and the coolant was original, so in obedience to Ford, I replaced it even though it looked fine. It keeps the cooling system healthy. And it bears mention that a good machine is the right way to handle coolant exchanges, because the waste stuff should never be spilled on the ground. We keep our waste coolant in a big bumblebee tank that Safety Kleen pumps out when it’s full.


Telltale problems include a wet and rusty area, a stain on a spark plug wire, a swollen hose threatening to burst and a rotten coolant elbow, which usually leaks famously.

Breaking Down
So why do some engines have nasty, rusty coolant at the prescribed coolant change interval and others look pristine? It’s pretty simple, actually. Coolant gets tired and breaks down over time, but there are other factors, and at least one of them is plain old atmospheric oxygen. A good, tight cooling system can’t ingest oxygen molecules every time the coolant expands and contracts and typically will be cleaner than a system with a bad pressure cap or some other atmospheric breach. If the cap has a dangly valve or bad rubber, I always replace it.

Then there’s the electrolysis bomb, which comes from poor grounding, out-of-balance PH in the system, etc. Electrolysis can be detected by measuring the voltage in the cooling system with a simple voltmeter.  A few millivolts isn’t a big deal, but when the numbers climb to more than a volt or two, things can get pretty dicey in there, and some vehicles seem more prone to it than others. Interestingly, there are radiator caps available with anodes like the ones used to protect aluminum boats against sea water electrolysis. The principle is that the anode sacrifices itself to protect the innards of the cooling system and prevents the engine’s cooling jacket innards from melting away.

This is the anode-equipped cap that sacrifices itself to save the engine. The one on the left has pretty much done that.

Coolant types abound, and because there are many articles talking about the different types, the only thing I’m going to say here is that some of them tend to break down sooner than others, and that when mixing water and coolant for top-off or replacement, the conscientious tech will use distilled water rather than tap water.  In some cases, coolant mixed with tap water will become cloudy and contaminated sitting right there in the jug on your garage shelf. That being said, almost nobody I’ve ever personally known about uses anything except tap water.

If a system is awash with big rust flakes, the water pump seal is subject to be shredded, so be careful to notice any staining if you can get a flashlight beam and an eyeball on the weep hole. The Front End Accessory Drive (belt and pulley system) is part of the cooling system too, so whenever you remove the belt for any reason, feel the pump if you can (some pumps may be out of reach at this point since they’re inside the timing cover and driven by the timing belt or chain) for loose or noisy bearings, not only on the water pump, but on the tensioner and idler pulleys.

When you have the transmission out, you might as well yank the flywheel to have a look at the expansion plugs and rear main seal. This Caravan needed both.

Under the Hood
I’ve known of frozen and destroyed engine blocks on diesel tractors, and when the coolant melted and drained out the cracks, it was pretty and green. It’s best to use a refractometer to when checking the coolant; they don’t lie, and they don’t cost that much if you know where to buy them. Tooltopia.com is a good source.

Visuals are a big deal when it comes to cooling systems. The first visual would be a look at the gauge when the engine is as warm as it’s going to get, that is, unless overheating is the issue. If it is, look around the engine compartment for rust or coolant stains, which can red-flag a leak. A cold running engine is not a healthy one, and that should be addressed pronto. Poor cabin heat can either mean the engine is low on coolant (and it won’t always overheat in that case) or it can mean the engine is indeed running too cold, which will usually toss a P0125 or a P0128 – the PCM likes for the engine to run in a particular temperature window. 

Sometimes the thermostat comes apart like this one did, but usually the spring loses some of its tension and starts opening at a lower temperature.

A cold running engine is practically without exception a thermostat issue, and on most cars thermostats are easy to replace. In many cases (certainly not all), you can replace the thermostat without draining the cooling system if it’s near the top of the engine, but keep coolant off the belts to avert the squeal. In other cases the thermostat may be feeding the lower radiator hose, so do your homework before you yank the wrong housing. Some of those gaskets are hard to come by on short notice and they just about always rip when the housing is removed. Also realize that if you replace the thermostat and the engine still wants to run cold (and I’ve been there), you might have to get two or three thermostats to get one that will work as designed. It would seem that the spring on some thermostats gets weak over time, because most of them look just fine when removed, even if the thermostat is the problem.

Service and Testing
Thermostats can be heated in a can of clear water with a temperature probe measuring the opening point, and while a stuck thermostat can be pegged that way, that method isn’t always accurate on a thermostat that causes an engine to run too cold. I saw a Cherokee that was running about 120 degrees, removed the thermostat, heated it in a pan and got the water to 200 degrees before it opened. I put a new thermostat in that one and the coolant temp rose about 80 degrees. I have no idea why it passed the coffee can test but failed in service. Thermostats are cheap anyway.

This tester is very cheap to build. You can connect it in place of a temperature sensor and dial in a reading that will cause the PCM to energize the cooling fan. Be aware, however, that some systems won’t operate the fan unless the engine is running.

On a similar note, I was finishing up a routine vehicle inspection on a Crown Victoria a few weeks ago and had the EASE Diagnostics Wireless Vehicle Interface connected to get some numbers on what the temp was (it looked to be running a bit cold on the gauge), and I saw a disappointing 160 F. Shutting the engine off, it took me about five minutes to throw a thermostat in that one (I had one in stock for a Victoria), and started the engine again. This time the big yellow numbers on my computer screen climbed from 160 to a comfy 210. Problem solved in record time, but you couldn’t look at the thermostat and tell there was anything wrong with it.

Next, a glance at the coolant bottle (whether it’s a surge tank or a pressure capsule) is in order to see if the coolant is on the full mark. Then squeeze of the top radiator hose is in order to see if there is pressure on the cooling system and remove the cap. I kind of like looking directly into the radiator, but on cooling systems that have a pressure bottle only, peering into that chamber is all you’ve got. If that plastic reservoir is heavily stained on the inside and you can’t see the level, I flush the cooling system and replace it (usually about $50).

This is a graphic explaining my home-made coolant burp tool. It’s cheap, easy to make and safe to use, but only suitable for vehicles with a cap on the radiator and a light duty surge tank like this.

Hoses seem to last longer these days than they ever did in the 1970s, but if oil has been leaking on a rubber hose for very long, it already has been compromised and shouldn’t be ignored. Sometimes a hose will have rotted from the inside out right near a metal connection point, but you can feel that while pinching the hose if you have knowing fingers. When replacing a hose, its good practice to clean the calcium crud off the neck where the hose will be clamped, else that bumpy stuff might cause a leak.

Then there are those plastic tees and elbows that either connect heater hoses or bend from the intake down into the water pump or timing cover, and those can fail without warning. They don’t cost much, and they should always be replaced if either connecting part is serviced. Plastic/aluminum radiators should be replaced at about 150,000 miles for the same reason. 

Comparing the ECT reading to the IAT reading after an overnight cold soak is a good way to find an out-of-range sensor. The one that matches ambient temperature is the one that’s telling the truth.

Then there are those funky spring clamps on radiator and heater hoses. I like the way they keep things looking factory, but if one is in a tough place to access, or really old, I’ll usually replace them with regular worm type clamps. I’ve seen metal fatigue cause spring clamps to break without warning but with obvious consequences.

The Fill
One of the most consistent lessons I have to hammer home to my new guys is that filling a cooling system isn’t like pouring water in a bottle or a bucket. If there are bleeders, you should do research to find out where they are, and manufacturer filling instructions should be followed to the letter using the right kind of coolant.  I tend to fire up a scan tool or my wireless interface so as to watch the coolant numbers in real time during the warm-up, and you can tell when the thermostat opens because the coolant temperature will take a shallow dive when it finally happens. Proper follow-up during a fill takes 20 to 30 minutes.

I like to hear the electric fan kick off and on four times if it’s got one (some cars don’t energize it until nearly 230 degrees, so do your homework on that too). Turn on the heater and keep watch for warm air there, but make sure you don’t choose a setting that brings the A/C online or the condenser fan will run all the time and mask potential problems. The fan should cut on and off; if it stays engaged and doesn’t shut off and the engine temperature continues to rise, there are problems. If the heater was working before but it’s not now, the system either is airbound or the water pump isn’t working right, particularly if the heater hoses are cooler than they should be.

Every so often one like this will come from the parts store, and I always reject it and send it back for a replacement. Some thermostat factory reps say caps with this dangly valve are designed this way to relieve system pressure, but if that’s the case I have two questions. First, why doesn’t every cap with the same part number have a dangly valve? Second, why have I never seen a dangly valve on an OEM cap?

Getting all of the air out of some systems can be a challenge. I have an Air Lift® vacuum filler tool for those more stubborn cooling systems and another homemade tool I use on systems with a radiator cap and surge bottle that works very well. It’s a cap with the spring and lower seal removed. It seals around the top of the radiator neck but allows coolant to come and go from the surge bottle unchecked. 

With the radiator as full as I can get it and the surge bottle tanked up to the Full mark, I fire up the engine, and my modified cap allows the cooling system to shove any air it’s burping into the plastic surge tank and then drink any coolant it needs from there as well. You have to keep coolant in the tank all the time and make sure the thermostat is wide open before you remove the cap to verify the radiator coolant level, and install a new cap.  There are three obvious benefits to this method. First, the tool is practically free.  Second, the system isn’t puking coolant all over the floor while you’re finishing the fill process with the engine running. Third, there’s a safety benefit in that there is no pressure on the system when you finally decide to remove the modified cap and replace it with the new one.

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About the Author

Richard McCuistian

Richard McCuistian is an ASE certified Master Auto Technician and was a professional mechanic for more than 25 years, followed by 18 years as an automotive instructor at LBW Community College in Opp, AL. Richard is now retired from teaching and still works as a freelance writer for Motor Age and various Automotive Training groups.

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