Automotive conundrum: What happened?

The history:

My pickup (05 Dodge Dakota) has been virtually trouble free for the 10 years that I’ve owned it (bought it with 4k miles on it in 2006). No leaks, no issues other than routine maintenance. In particular, the coolant temperature gauge has consistently and faithfully read a little bit below the mid-point the entire time, once the engine’s warmed up. Maybe a hair higher in summer, and a hair lower in winter, but still pretty much in the same place.

I had the cooling system flushed and filled with long-life coolant in 2012. Haven’t seen any leaks, nor noticed any change in the behavior of the temp gauge.

The situation:

So I take my pickup into the fast oil change place by the office to get the oil changed last Wednesday. Goons at the place change the oil, and tell me that I’m low on coolant, and that they’re adding some to top it off. I think “Ok… I haven’t checked it in a while, maybe the overflow tank was a bit low. No big deal.” They also tell me that I might have a slight coolant leak, but that they couldn’t tell if it was that, or some that may have spilled when they were adding coolant. Again, not a huge deal.

After driving out, I notice the temp gauge ABOVE the halfway mark. This hasn’t happened in 10 years of driving it. So I drive it a while at different speeds, etc… and notice that it is fine while at highway speeds, but gets hottest (without actually overheating) while driving at low speeds, especially stop and go type traffic. I google that, and find out that’s indicative of low coolant (?).

I think “Low coolant? Didn’t they say they just topped it off?” I topped off the overflow tank at lunch time, because it was really, really low.

So I let it cool off after driving home (it got hotter, but not overheating hot), and the following morning I checked, and the overflow tank was still low AND the radiator was low as well. Weird. So I filled up the tank and the radiator and put a bottle of that Bar’s Leaks stuff in as well. That did the trick- temp needle is back where it belongs, and the levels are staying steady.

So the big question is- what happened? Did the oil change knuckleheads turn the radiator petcock by mistake and let out a bunch of coolant? Did the temp sensor or thermostat or something stick and then release? Were the knuckleheads not telling me something?

I find it really perplexing that I’d have a vehicle that would read fine on the temp gauge until those guys fiddled with it, and then suddenly it starts threatening to overheat, and then doing exactly what they supposedly did remedied the problem.

Anyone have any ideas or theories?

I have seen this problem on a friend’s car. It’s called “poking radiator with a screwdriver during cheap oil change.”

I’ve seen this problem and it’s called “minimum wage lackey at quick-oil-change place is instructed to check fluid levels but doesn’t know better than to open radiator cap on a hot engine.” A lot of coolant will spew out when this is done, and it’s not really possible to get the same amount back in until the engine cools down completely.

The level in the overflow tank may or may not have been low before the pressure cap was removed. If it was low, the vehicle may have developed a small leak, or it may have lost a little due to evaporation. The Bar’s Leaks may or may not have been needed, but it didn’t hurt to add it – it might even delay some future leakage.

ETA: In my observation, personnel at “low-price” chain operations are trained to sell, not to have good mechanical judgment. Unfortunately, even something as simple as an oil change can be screwed up by someone ignorant enough.

The coolant system is a closed system. If you are losing coolant it is either leaking out or burning off.

Some coolant leaks are easy to find, others not so much. The leak can occur in a hose, radiator or water pump. If the water pump is going out it will slowly leak out of a weep hole in the bottom of the pump. Hoses can fail from the inside, and look good on the outside. Radiators can develop seeping leaks along seams or hose connections. Coolant leaks are harder to trace than lubricant leaks due to coolants thinner viscosity and lighter color.

Getting underneath the car and trying to trace drips back to the source is difficult. I clean and dry everything then spray the suspected area with powdered foot spray. The leaking fluid will leave a trace in the powder and can be followed to the culprit.

Burning off coolant occurs when a head gasket fails. The coolant is under pressure in the system, and if a head gasket fails the coolant can be forced into the combustion chamber and burned off as the engine fires. Sometimes this can be seen as white steam exiting the exhaust pipe. If you’re losing coolant and find no trace of a leak, i’d suspect this.

Regardless, losing coolant can cause substantial damage if not repaired. Engines can quickly overheat and fail and the heads can be easily warped
If the hoses, both radiator and heater, are original they are eleven years old and ready for replacement anyways. The system can be pressure tested for head gasket leak downs by a mechanic. It is also much easier to trace a hose or radiator leak when the vehicle is on a lift. Repair this issue now and will be much cheaper than burning up an engine or being stranded on the side of a road.

Beauregard, I’m sure you’re a wonderful person and what you’ve posted is essentially correct, but it has nothing – NOTHING – to do with bump’s situation as he’s related it. His coolant loss was not from a leak of any kind, and there’s nothing to “repair now,” other than his choice of service facility. The amount of coolant loss he’s described, in the stated context, was dumped out when some idiot opened the pressure cap on a warmed-up engine.

Citation? Because otherwise, you’re castigating a knowledgeable contributor on the basis of your completely unsubstantiated speculation.

Please tell me you put the Bar’s Leak in the radiator when it was warm enough outside to not need you cars heater cuz ya don’t want Bars leak in your the heater core. That’s an expensive repair. Also, foot powder is good for finding leaks but baby powder might be a little cheaper and works in the same way. Good luck.

Phu Cat

Regardless of whether it actually was caused by an idiot opening the radiator cap on a hot engine, the amount of coolant loss in the time frame described by the OP appears to be more consistent with that speculation than with the situations brought up by Beauregard Porkypine.

I don’t know that it’s related to a leak, but the weird part is that a leak resulting in a slow loss of coolant should also be accompanied by a corresponding slow rise of the operating temperature. Or if nothing else, the temp gauge should have shown something other than the same rock-stable temperatures that it had shown for the decade leading up to it.

That’s what has me so baffled; not so much whether or not I have a leak, or how to fix it if I do. The fact that it was the same for so long, and then the oil change guys do something under the guise of adding coolant, and then it starts reading hot until I refill both the radiator and overflow tank, at which point it goes straight back to the same temp reading it’s had since I bought it.

I like **Gary T’s ** idea; that could explain it, if enough came out. I had to add about a gallon in total between the radiator and overflow tank of coolant/water mix.

And FWIW, there are NO drips or drops of any kind underneath from anything except A/C part condensation.

My long-term plan is to keep an eye on the coolant levels, and IF they actually change, then get it diagnosed and fixed.

Forty years of professional auto repair experience, having seen this very scenario twice, knowing that the totality of symptoms described and their sudden onset, along the lack of other symptoms, cannot be caused by normal leakage scenarios.

No, often the engine temperature and the gauge reading will not change gradually but will show normal until a tipping point is reached.

As I noted above, I’ve seen this exact thing before. There is nothing else that will cause the sudden loss of so great an amount of coolant (without leaving super-obvious evidence such as a burst hose), and there is no way it could have gradually become that low on coolant without symptoms showing up earlier.

Gary, I’m sure you’re a nice guy as well, but claiming to “Know” the totality of symptoms when they are merely described in a written post is over the top.
Do you know for a fact the operating temperature when the tech (goon) started working on the vehicle or are you assuming? You know for a fact this problem was caused by the cheapo oil change tech? It is an eleven-year-old vehicle. We were not told if the hoses have ever been changed or the radiator maintained. It is entirely possible that the overheating is completely unrelated to the oil change and are presenting themselves under coincidence.
I would be very surprised if in forty years in the repair business you have never been accused of creating a problem that is completely unrelated to what you worked on. I have seen this numerous times; i.e we change an exhaust system and the customer complains that the brakes now squeak and shudder. The fact is his brakes were shot when he came in for the exhaust work, but you would never convince the customer.

My point is, it is entirely possible that the cooling system in this eleven-year-old pickup may indeed have an undetected leak that presented itself coincidently with the oil change and should be repaired. In forty years of auto service you have surely seen coolant leaks that didn’t leave a puddle, right?

What’s wrong with presenting your idea as one solution of many possible without discounting everyone else’s as hogwash?

In closing, your theory is a possibility, but there are others.

Firestone is widely regarded as “If we can’t find a problem. we’ll make one” shop.

My cheapie oil change story: Stripped head in cartridge cover. Had to go to a machine shop for extraction.

I had a clutch problem. Took it to a very busy shop (usually means good work). I ask for a clutch adjustment.
“The clutch is worn out. Can’t be adjusted any further. Replace clutch for $1600”.
It is a hydraulic operated clutch. There was an air bubble in the hydraulic line.
Drain and re-fill clutch fluid. Clutch is fine.

You really do need to find an honest mechanic.

My best story:
Young guy figures he’s ready to have is own shop.
It is 4:30. His uniform is still stiff from ironing. No business that day, so he’s chatting with his buddies, being the important guy.
I offer the then-standard $80 to get a Check Engine code read.
“Well, it’s too close to closing time - come back tomorrow”.

I noticed the ‘low rent’ shop had a new sign a couple of months later. But he sure showed me who was too important to work when he could be the ‘big man’ to is buds.
Idiot.
It was an intake air temp sensor. a $50 part that shops wanted $200 part and labor.
Took me about 45 minutes to install a new one with quick-disconnect splices.

Thank you. I try to not be disagreeable when I disagree.

Of course we weren’t there, so we only know what the OP has told us. If he tells us wrong or omits something critical, it’s pretty much a garbage-in/garbage-out situation. Nevertheless, I find the OP’s narration plausible, and based on the assumption that it’s accurate, I think I can draw some firm conclusions.

I absolutely understand coincidence – if it never occurred, we wouldn’t have a word for it. In this case, however, the “evidence” we have doesn’t support it, and I believe that in the light of that evidence other proposed explanations don’t make sense. Let’s look at this:

For the sake of illustration, let’s assume the pressure cap was not removed. The vehicle was driven to the shop with no symptoms, then after leaving the shop it ran hot. Presumably, ongoing coolant loss just happened to reach the point where a symptom occurred during that short time frame.

Note that later, after the addition of a significant amount of coolant, the symptoms disappeared. This eliminates other possible causes such as the thermostat, radiator fan, blown head gasket, etc. Low coolant was clearly the cause of the problem.

Yet at the shop they added coolant. If they didn’t open the pressure cap, they added it to the overflow jar. But the OP found the level in the jar quite low, showing that the coolant they added was taken into the radiator. So how is it possible that the shop put in MORE coolant but the vehicle ended up with LESS coolant, as evidenced by its running hot? It isn’t, and this story just doesn’t make sense.

What the evidence at hand tells us is that the vehicle, with no detectable coolant leaks and no malfunctioning cooling system parts, lost a bunch of coolant between the time it was pulled into the shop and the time the OP noticed it running hot, shortly after leaving the shop. The only plausible explanation for this is that someone removed the pressure cap and a lot coolant spewed out. Reinforcing this notion is the fact that this has been known to happen, when poorly trained entry-level service personnel – who are typically employed by quick-lube shops – are entrusted to perform procedures they don’t fully understand.

If there’s a good case to be made for an alternative explanation that accounts for all the facts as we know them here, I’d love to hear it. For this particular series of events, though, I don’t believe one exists.

There’s your problem. Stay out of those places, right, Rick?

Gary, maybe the symptoms disappeared. Maybe not, though.

A slow leak may take a while to present noticeable low fluid. I’ve seen hairline cracks in the bottom of the overflow reservoir that only leak under pressure (engine running). I’ve seen plastic elbow fitting on the overflow hose seep and leak only under pressure. I’ve seen water pumps on the way out only leak while the engine is running. I’ve seen head gasket leaks that drain off fluid slowly through the combustion chamber. None of these really leave telltale coolant puddles when parked.
There are lots of ways to slowly lose fluid until something like an overflow tank lets loose all at once (usually in a stop and go traffic jam…).

My point is, while your theory is certainly well thought out and plausible, The OP would do well to have his system checked out to make sure nothing is going on.
A system checkup, including a pressure leak down test for the head gasket, by a qualified mechanic, would be less than $200 around here. That’s money well spent on an eleven-year-old truck, with the alternative being a fried engine.

I do hope Gary’s theory is right and all is now fixed. But Coolant issues should be taken seriously, and I would still recommend having some check-up work done.

Gary T almost has to be right on this. That’s the only way you could instantly lose enough coolant to cause an overheat without seeing steam or a visible leak.

My credentials are being a degreed mechanical engineer, general gearhead and engine design fanatic, and have done most of my own automotive repairs for 40 years.

Your stop leak was probably a good idea. Dakota’s are known for failed heater cores and the whole dash structure has to be removed to fix it. My '97 Dakota had a slow drip into the passenger floor area and Bars Leaks pelletized formula has sealed it for 8 months now.

And never go to a quickie oil change, they disassemble stuff, put it back wrong, lose parts…even Walmart is better.