Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Thermostat trouble

I put my 1993 Toyota Camry up for sale and have had a few interested buyers. We’ve been driving it ourselves plus the test drives, and everything goes well. We’re in Phoenix, AZ, and so the air conditioning is always on full blast.

Today a guy calls and wants to buy it, but he has no car and so I take it to him, about 1.5 miles away. He gets in the driver’s seat and pulls out of the parking lot: BAM! The thermostat shoots up! He of course declines to drive any further, so I wait 15 minutes and chat with him about anything other than cars, then drive it home. I stop twice on the 1.5 mile trip home because of the thermostat going through the roof.

However, on the third and last leg of my journey home, as the thermostat rises, all of a sudden it just stops, and immediately falls back down to normal, and just sits there, perfectly between the C and the H.

What gives? And when I resolve the issue, what is the best way to approach the buyer so he will want to look at it again?

Before you take the car to a mechanic and fall victim to problems stemming from miscommunication/misuse of terminology, I want to point out that the temperature gauge was “shooting up” during the test drive. The thermostat is internal to the engine’s cooling system, and while it certainly may be part of the problem, the thermostat is not what you observed.

That being said, I would first suspect the temperature sending unit (which is screwed into the engine block) as being the culprit here. Before a temperature sending unit stops functioning completely, it may give inconsistent readings, as may be the case here. If this is the case, the engine’s temperature may be normal, but the bad component may sometimes send the wrong information to the temperature gauge on your dashboard.

It is also possible that the sensors that activate the cooling fans on the radiator may be working inconsistently. In this type of situation, your engine may actually be running very hot until the sensors belatedly activate the cooling fans.

Other possibilities include a thermostat (the part that is internal to the engine’s cooling system) that is not opening promptly, thus causing high engine temperatures.

If the engine is really running hot, it can quickly cause major damage to the engine. As a result, you need to get this car to a mechanic a.s.a.p. before damage results. If you are lucky, you will only need a new temperature sending unit or new temperature sensors for the cooling fans, or a new thermostat. If you are not lucky, you may have warped the cylinder head or caused other types of damage to the engine from driving with a high engine temperature.

When the problem is resolved, show the repair invoice to this particular buyer so that he can see what the repair involved. Hopefully, he will still be interested in the car.

Replace the thermostat. I recommend a 160 degree one since you live in Phoenix. I used to live in Sierra Vista, AZ and ran them in both of my vehicles. They always managed to get to 200 degrees but not much more. Your thermostat is sticking. Time to replace it.

Assuming the problem is not caused by an temperature sender lead making an intermittent ground (and pegging the gauge out) then it’s likely the thermostat is acting up.

JMHO, but a thermostat is a maintenance item as far as I’m concerned. I think they should be replaced on a regular basis. (say every 3-4 years at most)
Many a head gasket, or even an engine, has been roasted due to a 5 dollar part. It’s best to head off a problem before it occurs.

If the engine really is overheating that bad then continuing to drive it home is a mistake. Overheating cooks engine oil, weakens head gaskets at the least, and can even seize piston rings in their ring lands or remove the ring temper. (hello oil burner)

While I agree that the tstat should be replaced, I respectfully disagree on using a 160 degree tstat. Sure, in the hot weather, you’ll be running well over 160 (and even over 200), but there will be many times when the outside temps will be cooler and the engine won’t run at the temps the computer and sensors are designed to run at.

OEM thermostat will be fine unless another issue is involved.

recommend a 160 degree one since you live in Phoenix.

A common error. It would seem that using a lower thermostat setting would help keep your car from overheating, but no.

It only means that your car will try to stay at 160? rather than the 195? or whatever the optimum temperature is. When the coolant temperature is over 195? either thermostat will be fully open and there is no difference to the car. However when car is operating normally the 195? thermostat will keep the engine at the design temperature. The 160? thermostat will keep the engine cooler than the design temperature causing additional wear, and reducing efficiency, reducing mileage.

Stick with the recommend thermostat for long efficient life.

If you car is over heating a lower temperature will not help it.

That sounds really good on paper, but I think I replaced my last thermostat in 1978, Yes it is great advice but 90% of cars with 100k have never had the thermostat replaced i would guess. It would be a good start to replace the thermostat and go go from there.

I used to replace the thermostat with every other coolant change, IOW every 4 years. The old ones always felt sticky working them by hand. Now that I have a car with ‘long life’ coolant I plan to change the coolant and thermostat every 5 years. It’s cheap insurance. I’ve seen failed thermostats in other peoples cars.