Thanks in advance for any input.

So my symptoms are that the car drives fine - no issues - but the temp gauge tends to fluctuate between 3/8 and 5/8 of the gauge... for no apparent reason - I can't make it "climb" by just idling, or make it drop by going faster, or changing gears to change the RPMs... it's not "overheating" - i.e. climbing without stopping all the way to H. When I turn on the heater the gauge definitely drops down... turning on AC doesn't not cause the temp to keep climbing - I'm going to go verify the fans after work - but I'm pretty sure they come on with the AC - not sure if they came on with the fan temp switch.. I'll check that today.

Radiator is full, and overflow tank has coolant in it.

I read through the DIY overheating thread - but this is a bit odd since it doesn't "technicallly" overheat nor run totally cold....

I'm thinking partly sticking thermostat? or maybe a bad radiator cap? I dunno - hence I'm consulting you folks

Cheers.

 

It sounds like you have a good start on the diagnostics. Could also be a bad water temp sensor.

 

Are the temp changes real or perhaps a faulty gauge or sensor? I would rule this out before replacing any parts.

If gauge movements are abrupt (few seconds), then a faulty gauge or sensor is likely since coolant can't change temp rapidly. There are diagnostics to check the gauge movement in Honda shop manuals. Should be same for most years.

good luck

 

Thanks for the help so far! Here is some more info.

1. So I just drove home, 17 miles - temp was ok (where I am used to seeing it 3/8ths of the gauge) then part way - it moved up to just over the 1/2 mark - stayed there. This movement from 3/8 to 1/2 is not "sudden" - i.e. it does not just jump, but moves to that temp over 20-30 seconds.
2. I pulled into driveway - gauge was still at same 1/2 way mark (or so) - popped hood- fans are not on. Upper radiator hose is hot, lower one was markedly cooler - so I believe the thermostat is at least opening (perhaps finicky, but not sure yet).
3. I turn on AC - both fans kicked on, I turned off AC, fans turned off (only let AC run for a few seconds to make sure fans turned on) Gauge stayed in same spot.
4. I turned off car, and restarted - Gauge returned to 1/2 way mark (I shut down/restarted immediately - i.e the result was what I expected).
5. After a minute, gauge seemed to inch a bit over 1/2 way mark and then a few seconds later i hear a click (relay) and BOTH fans are on..
6. Gauge within 10-20 seconds returns to 3/8 position....

I am new to the Honda family - do both fans work in tandem always? or should the radiator fan have kicked in sooner?

Thank you again for all the input - I am definitely doing as much research as I can in the matter to try provide good info for you guys to help with as well as to try solve the problem myself. I do not have the factory manual - I have been trying to buy one forever for the 6th Gen - but Helm is always backordered. But I am going to keep looking

Cheers

 

Everything is normal except your temperature excursions over 1/2 mark. Both fans should run at all times on your model. A good cooling system control barely moves temp at any time. It may be your thermoswitch A, which controls temp w/ AC off is coming on late. It should engage about 195F. From your description the temp gauge or sensor don't seem likely to be the problem.

Earlier models had a single cooling fan run w/ keyswitch OFF to reduce heat soak runup in cylinder head temp, but I think they stopped that w/ your model or earlier perhaps.

However, a faulty thermoswitch A would not explain why the temp is moving up while driving. My experience is that temp is controlled well by modest air flow from forward movement and cooling fans don't come on until you're driving slow or stopped.

You could have a thermostat that is sticking sometimes slightly closed, causing warmup, then perhaps opening quickly and cooling to returning temp to normal.

A thermostat is relatively inexpensive, and starting w/ this component may be a good bet to fix your problem. OEM Accord thermostat is best IMO.

good luck

 

I agree on changing the thermostat. Ony go to the dealership for one. They are around $15 and open at the proper temperature for your car.

 

Texashonda and PAhonda - thanks for the feedback. I'm going to do a full cooling system flush this weekend as well as look at replacing the thermostat.

I do have a question about the thermoswitch for the fans (Thermoswitch A that Texashonda refers to) - will that only kick in once the thermostat is completely open - or should it close anytime the temp reaches 195 deg F (assuming factory part is still in there)?

I agree with you Texashonda - that on a moderate 70deg day going 60mph on the highway - there should be sufficient air cooling that the fans should not be needed - and also - that the needle should mostly stay "fixed" on a cooling system that is operating correctly. That has been my experience thus far on other vehicles I have owned... hence my concern and post Thanks for all the feedback so far.

Related to this - what's the best way to "measure" the actual temperature of the coolant? i.e. so I can get an idea of what the actual temp is when I'm seeing the gauge above 1/2 way...

 

Thermoswitch A is a simple mechanical thermal switch designed to close contacts at 195F and enable fans. It has nothing to do w/ thermostat, another component. It's located on the thermostat housing on earlier models. Flush the cooling system w/ lots of fresh water to clear the flush chemical before adding new coolant. I never pull the engine block drain plug because its' difficult to access.

Best way to measure the coolant temp is to use an IR temp gauge and "shoot" the thermostat housing. This is accurate to w/i a few degrees. They are relatively inexpensive on ebay or other sources.

If you've maintained the cooling system, the flush is unlikely to do any good, but won't hurt.

good luck

 

TexasHonda - so here is perhaps more of theoretical question.

The temp sending unit is measuring the coolant as it exits the engine toward the radiator - while the fan thermistor is in the thermostat housing which is on the inlet to the engine cooling path. So if my gauge showing a hotter than normal temp - perhaps due to restricted coolant flow from a sticky thermostat - why wouldn't the thermistor trip the fans on sooner (since hotter coolant on exit from engine would mean hotter coolant on inlet too (this assumes that the radiator cools the coolant by a fixed amount regardless of temp of coolant into the radiator and also that the coolant path through the engine always adds a "relatively constant" gain in temp, i.e. if you push in 180 deg coolant on inlet side, you get 190 on exit, 200 on inlet, would give 210)...

I'm not sure how best to phrase it - but basically, let's say the radiator is able to cool the coolant by 10 degrees, if my car is running at 210 instead of at 200 (deg F) (because of a partially closed thermostat), the coolant going back into the block in the first case would be at 200 deg - so the fans should have already switched on right to compensate for the fact that the engine is running hotter, right?

Like even on my highway scenario, where the temp gauge climbs above 1/2 way mark even while driving 60mph - I would expect my fans to have switched on... regardless of thermostat state...

Also - thanks for that pointer to those IR temp sensors - I will definitely get one (soon I hope) to add to my toolkit! A tool I never knew existed. I Can use this on the exit side of the coolant from the block to see how hot it is there as well right? as well as on the inlet side, as you suggest to see when the fans do trip on.

This is a time when a phone call would make a world of difference I hope that somewhere in the above rambling, my hidden point is clear

 

There are several possibilities for your problem and it is not possible to definitively identify the problem from available information. You could have stuck thermostat, dirty or partially blocked radiator, defective coolant temp sensor, or defective thermoswitch A (not likely, but possible). It is possible, but not likely that a combination of problems is causing your symptoms.

You could not detect your fans coming on at 60 mph w/o a tell-tale light inside the cabin. Too much extraneous noise.

When you have multiple possibilities it's usually best to proceed from the most likely or perhaps least expensive to implement. Replacing thermostat is inexpensive and has high probability of fixing your problem.

good luck