Cooling System Service

Often Overlooked

One of the most comical things I’ve heard some people say is that they don’t think they need an oil change because the car still runs good.  And those people are totally oblivious to the coolant that carries away engine heat.

Then there are some people care a lot about their cars but know very little about where things are under the hood, even if they do care deeply about what goes on under there.  I knew of one young woman who saw a coolant level warning light on her Jeep Liberty and was concerned enough about it that she opened her hood, got her water hose, and filled the crankcase with water.

Another customer recently came to me with her Buick smoking and making strange noises. She said she had seen the oil light come on and so she added oil, but she wasn’t sure she had added enough.  I pulled the dipstick and we found that it was about five quarts overfull.  When I asked her why it had so much oil in it, she said she didn’t know anything about the dipstick – she just figured she needed to add oil until she could see through the filler cap hole that it was full.

But there are some drivers who are car-conscious enough to check and change the oil regularly, and they’ll even check the rest of their fluids, but too many don’t ever think of replacing the coolant or doing anything else to the cooling system until it springs a leak or an overheating episode happens. Oil changes happen regularly. Coolant changes every sixty thousand miles tend to be forgotten.  It’s sort of like the transmission – some folks don’t consider doing anything to it until it starts giving problems.  And a neglected cooling system tends to develop a few problems that can’t be easily dealt with, and some of the fallout from such lassitude is more or less permanent. Flakes of rust shred water pump seals, heater cores, and radiator fins, and used-up coolant stops protecting the metal parts. I’ve repaired overheating problems in some cases by just replacing old coolant.

From our side of the service aisle, it’s a foregone that cooling system service makes a LOT of difference, and it’s a great (and necessary upsell) on vehicles that are in need. Checking the vehicle’s maintenance record and schedule is a legitimate practice too (if there is one).  If you follow the manufacturer recommendations at the intervals they publish, it pays off in the long run for the customer as well as the shop.  It’s a win-win, but you must sell it!

Plastic Parts That Fail

To save weight, car manufacturers have been making lots things out of plastic for decades now, and many of these plastic parts carry hot coolant, which, in many cases has been a tremendous repair boon for those of us who wrench for a living. How many shops could fill the back of a pickup with plastic coolant-carrying parts we’ve replaced over the past six months?

Awhile back, a lady came to me with a high mileage Honda Accord and asked what I would do to reduce the likelihood of mileage-related unscheduled maintenance.  One of the several things I suggested to her was that we replace the radiator and the coolant along with it. Why? Well, most of us have seen more than a few engines destroyed because of an old radiator that cracked on the highway, dumped the coolant, and led to a meltdown. Then there are those radiators that leak from the rubber seal between the core and the tanks.  That happens even on lower mileage platforms, and sometimes it happens with replacement radiators if they’re cheapies.

And there are those crummy plastic elbows GM used to pipe coolant through the belt tensioner on turn-of-the century 3.8L platforms, but good metal replacements are now available for those.  And there are also the plastic intake manifolds that like to split and plastic-and-silicone manifold gaskets that die every day and start dumping coolant everywhere.  Most of us have also replaced leaking plastic thermostat housings on Ford Explorers and those annoying plastic 2.7L water outlets (the one that comes with the ECT sensor in it).

If you put a heater core in a mid-2000s Nissan Pathfinder, you may find that under hood heater hose manifold and pipe assembly brittle to the point of dreadful fragility, and since it includes an electric water pump, it’s about 250 bucks.

The point is that there’s nothing wrong with upselling items like this to protect a customer from catastrophic breakdowns. Again, changing failure-prone plastic parts on familiar platforms that are high mileage helps protect the customer from later loss. Simply servicing the cooling system might not totally prevent plastic part failures, so on a failure prone part that doesn’t cost a lot and isn’t hard to change, selling one is a good idea, even if it’s the plastic intake manifold on a Lincoln or a Crown Victoria. Those like to leak in various places as well. But be careful to buy good parts. We’ve had to replace radiators a second time because the first replacement part started leaking at the tank/core joints after only a few thousand miles.

We replaced one plastic radiator on a 2005 Caravan (it seems like we work on a lot of those) that wound up with a percolating coolant issue after we replaced the radiator, and it turned out that the neck of the radiator was built just a bit out of spec – even with the right radiator cap installed there was almost no spring tension applied, and so the coolant wasn’t under pressure, and it would be boiling whenever she stopped the vehicle. You could remove the cap with a thumb and a forefinger.  The radiator cap’s bottom seal didn’t even have a signature mark where it had been pressed against that inside lip. Experimentally, I took another new cap I had, removed the gasket, and worked it onto the new radiator cap, stacking the gaskets to apply more pressure, and the percolation stopped.  The radiator still had to be replaced with another one.


The Cap Debate


Certainly one of the more interesting issues I’ve run into more than once over the past several years is in regard to brand new radiator caps with dangly vent valves.  If I pull a radiator cap off an older system and see a dangling vent valve, I’m replacing it. But when the new Stant cap comes with a dangly valve, I get sort of bothered, and I make the parts guy find one with the same part number that has a tight vent valve. And he always can, it seems. When he combs his inventory, some of the same part number caps will have dangly valves and some won’t. That in and of itself is troubling, but Stant calls these danglies “partial pressure” caps.

In a “partial pressure” cap, the vent valve is free-hanging by design – there is no spring to close it, just a small weight to make it dangle. It is supposed to close only when system pressure rises high enough to cause coolant flow volume that can overcome the weight of the valve and push it shut. Thus, in these systems, the cooling system isn’t pressurized until it gets hot enough to put sudden pressure on the cap. At that point, the sudden pressure/flow that hits the cap is supposed to push the vent valve closed and then pressure increases in the cooling system. Why do this? Well, they say the system doesn’t need to be under pressure until it becomes necessary to raise the boiling point of the coolant. Supposedly, this is easier on the solder joints and other “weaker” places where building pressure can cause leaks, and I’m not a college-trained engineer, but my question would be that if those joints can’t take the pressure early on, will they even be able to handle the pressure after it rises?  This is a peculiar strategy to me.

This debate may not be worth having, but I don’t like replacing one dangly vented cap with another one, if you know what I mean.       Caps are cheap, though, and replacing the cap is typically a good idea.

Most of today’s cooling surge-tank type systems don’t have that kind of radiator cap anyway, but there are multiplied thousands of vehicles on the road that do.

Much Ado About Coolant

With all due respect, we’ve seen more problems with Dex-Cool than any other coolant. That orange liquid loves to turn to orange mud on systems that haven’t been serviced according to the book, and it’s very difficult to get that junk out of a system once it’s there. We’ve used all manner of methods (including “CLR”) to try and get rid of that stuff, but it usually takes repeated services over time to make it happen.

We worked on one 2006 Impala that, when you removed the filler cap, had what looked like modeling clay clogging the filler neck.  We flushed and flushed that one and eventually replaced the radiator before we finally got it clean enough to be trouble-free.  Green coolant went back in, and we finally got just about all of that stuff out, but periodically some of it will break loose and make an appearance when we’re servicing that one.

On my personal vehicles, I follow the maintenance guide on everything from oil changes to coolant exchanges.  I have a 2007 Taurus and a 2007 F150, both of which use Motorcraft Gold, and when I replaced it in both vehicles at the required interval, the coolant I was pushing out looked as good as what I was putting in. Personally, I like the Motorcraft gold coolant best of all, but Ford has moved on to other formulas and colors now.

We presently use a Robinair coolant exchanger that works well, and before I exchange the coolant on a nasty one I like to push about fifteen quarts of water through before shoving the coolant in, but it works best when you remove the thermostat instead of letting the pressure push it open, and replace the ‘stat when you’re done.

A P0128 code basically means the engine is running a bit cooler than the PCM is programmed to accept.  The P0125 code usually means a thermostat is needed, but on some Toyota platforms it can mean the O2 sensor heater isn’t working and closed loop isn’t happening soon enough or at all, and you may not get an O2 heater code. If you’re working on a Camry that seems to be running warm enough but still throws a P0125, look at the O2 heater. The problem is that some new thermostats open too soon. I sometimes had to replace one two or three times when I was at the Ford dealer to get one that would get warm enough.

It’s a no-brainer that old coolant needs to be captured during service and stored for disposal – we have a Safety Kleen bumblebee out behind the shop where we dump our tired old coolant and they come around to pump it out when they take our used engine oil and our drum of used oil filters.

Without doing a lot of internet research, I’ll say that, in my experience, that mix-with-anything coolant the parts stores sell has worked well for us in most cases, but I may get my ears combed down with emails for saying that.  If the system is clean and regularly serviced, coolant is coolant, for the most part, in my opinion. There are exceptions. I try to get the right coolant for those exotic Asian and European cars whenever I can.

Using distilled water is optimum when doing the 50/50 mix thing; sometimes tap water will create problems, but most shops use it anyway with few issues.

Hoses and Stuff


Anywhere there has been oil seepage that attacks a rubber coolant hose, those hoses tend to get soft, flabby, and unreliable.  And don’t we all love those OEM spring clamps that can be so annoying, especially when one of the ears snaps off on one that feeds the heater core and those connections are ‘way down there almost out of reach?  Be careful of hoses that are dissolving from the inside out, because they’ll look good right up until they spring a pinhole leak.  You can usually squeeze the hoses with a practiced hand and catch this early, though.

Speaking of heater core connections, be careful of replacement plastic quick-connects that don’t fit right – sometimes they’re too tight to fit properly on the heater core pipes, and on some late 90s-early 00s F150s they’re totally out of sight under the cowl when you shove them on there, so you can’t tell if the plastic retainer has passed the pipe rib or not.  You might think they’re on all the way because you can’t pull them back off, but that’s because they’re a tiny bit too small to fit right. And then when the engine gets warm they inevitably blow off in those cases, and that’s bad news.  If you can’t get a good replacement quick-connect in short order and the customer is waiting, it might be a good idea to dump the plastic quick connect, shove the rubber hose past that lock lip and put a screw clamp on there.

Unserviced cooling systems (or systems that have been filled for awhile with nothing but water) may have cavitated water pump reaction services and partially dissolved impellers, so if you know the cooling system is full and you don’t have good heat, check for good flow. If the impeller is plastic with an aluminum hub, sometimes those get loose on the shaft and cause similar issues. To check for flow, we pull the hoses off the heater core and put a clear hose from the local hardware store between the inlet and outlet heater core hoses to see what’s going on. It’s a neat way to find bad water pumps and clogged passages, because you can watch the flow happen. You can connect a water hose to the heater core and check for flow through as well while you’re at it.

Pressure testing is a good thing to do, but you need a really good pressure tester, and I despise those that have the stupid one-size-fitz-all rubber cone, because they tend to blow out and make a mess. I want a set that has a cap to fit most every system.

Bleeding the cooling system is an all-important task – always turn on the heater – if it was working before but it isn’t working after the fill, you may need to do extraordinary things to get the air out.  On a 2005 Pathfinder we just finished, (heater core, heater pipe manifold, etc.), we had to jack the front of it up at a very steep angle and add coolant to get all the air out. Initially, one of these will seem full and won’t usually be overheating, but we had no cabin heat until we raised the front of it and poured in another half-gallon of coolant. Watch for that.  Nissan Quest is similar – raise it up in the front, put a funnel full of coolant mix on the radiator neck, and slap the throttle a few times. On the ones with old fashioned radiator caps, I use a doctored cap with the spring and seat removed so that it seals only around the top of the neck, and as the engine heats up, that lets the system drink from the degas bottle and get rid of its air very easily, but you have to keep an eye on the coolant level in the degas bottle.

Vehicles with the thermostat in the lower hose are obviously easier to bleed than those that have it in the upper hose, because the block tends to fill through the open top hose. I first saw that setup on VW Rabbits and some of the old 2.8L Ford V6s back in the day, but it’s everywhere now.  On some platforms I like to fill the block through a heater hose, which bypasses the thermostat. Always check for shop manual procedures on unfamiliar platforms. R.W.M.

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