The car's temp gauge is right in the middle until it gets tested for emissions. Idling in drive with the brake on behind a line of cars in traffic or drive thru doesn't raise it.
Both hoses and the thermostat were replaced with Honda parts less than two years ago. The temp sender was replaced a couple of months before that. When I did the hoses, I should have taken the radiator to the shop for a flush but did not. It is (as far as I know) the original radiator. That's what I'm going to do today.
Any insights or suggestions would be appreciated.
I will post the follow up when I get it fixed.

 

Does the radiator fan come on when it gets hot?

Which temperature "sender" did you replace?

The one in the thermostat housing - THAT's the one responsible for switching the fan on while the engine is running.

 

Forgot to mention that both fans are coming on. I believe the temp sender was in the thermostat housing. I didn't do that repair.

 

So the temperature gauge should be at about 1/3 or 1/4 of the way up when the engine is at normal operating temperature.

You said your gauge is in the middle normally. Does the gauge go towards hot when you have the emissions tested? When does the gauge move towards hot under normal driving conditions?

 

Did you check the coolant level in the radiator? Proper mix of coolant and water in radiator?

 

This is the mystery to me. It has only overheated during emissions tests, so it won't pass. During normal driving the gauge is just a bit below the middle mark.
There is adequate coolant in the radiator and reservoir.
I don't know how to duplicate the circumstances that make it overheat without going to the inspection station.
Other than that, the car runs well and the check engine light has not come on.

 

How many miles are on the car? When did you have the timing belt replaced? Was the water pump replaced when the timing belt was replaced?

Some parts stores have a radiator pressure tester that you can rent. You pay for the tester and get a refund when you return it, so it is essentially free.

Your system should be able to hold around 15 psi. There are also adapters for the radiator cap. The cap should hold pressure until the max stamped on the cap (1.0 or 0.9 atm).

 

There are 201,000 miles on the car.

The timing belt, water pump, drive belts, seals and tensioners were replaced in February of 2010 when the car had 191,211 miles on it. At this time the distributor sub assembly was replaced with a 1993 rebuilt unit along with the temp sender. This work was done by a reputable independent shop.

I took the radiator to a radiator shop and had it flushed and tested and was told it is not leaking and should be fine. They did not test the cap but I might replace it with a new one just to be safe. When I removed the radiator, I noticed the bottom hose clamp was just a bit off the hose edge so I was pretty vigilant when I reassembled it. I was also careful to bleed the air out as I refilled it because I had neglected to do that after I (yes, me not the good shop) replaced the hoses and thermostat in April 2010.

After I carefully put things back together today, I started the car while it was still on the stands to look for leaks. There were none. Both hoses got hot so I'm assuming the thermostat opened. But the car didn't get hot enough to turn the fans on. They only came on when the A/C was turned on. The gauge needle stayed a bit below the middle line the whole time.

 

My best suggestion is to call the emissions place to find out what they do to test the car and run those tests.

Ask how long and what rpm do they do the tests and try them in your driveway. The fans should turn on definitely after the needle reaches the half way point.

 

In California, there are two types of emission tests. One is with a dynamometer. However, for that test, large cooling fans are used if the ambient temperature of 72 degrees or higher. Page 5 of the following for California emission test. I regularly see those large cooling fans at the smog test shops in California.

smogcheck.ca.gov/80_BARResources/ftp/pdfdocs/Smog_Check_Procedures.pdf

I'm not sure how Texas does their testing (I see your location says Texas) and whether they also use cooling fans, which may help in your case if the overheating has only occurred during the emission test.