97 Accord 4 cyl. I had this problem once before and I replaced the thermo switch located on the lower radiator hose. If I have my facts correct, the switch on the lower hose housing controls the radiator fan (passenger side) while the engine is running, and the switch on the upper hose controls the fan when the engine is shut off. I have checked all fuses and checked the radiator fan relay. I've jumped the switch connector on the lower hose while the temp gauge shows almost 3/4 the way up, and both fans will turn on. What the heck gives? I've replaced the switch on the thermostat housing twice and no results. My thermostat IS functioning because my lower hose is cold then gets hot after warm up. Any ideas?

 

So you jump the switch with the car on and the fans come on....correct?

If so then there is something worng with a switch or sensor.

Do you have a way to verify the engine temp? Some meters have a temp probe, there are IFR temp readers you can buy - I think Harbor Freight has them for ~$30.

If the engine temp is above the "set point" of thermo a and the switch is not closing....then either the switch is bad (I know you said you replced it) or the coolant is not getting to the switch - air in the system.

 

try turning on the AC. it might be the fan relay if the AC doesn't make it turn on

 

poorman - Yes, I jump the connector on the thermostat housing and both fans come on with the key in the on position. I'm more than positive the engine temp is getting hot because the temp gauge got to 3/4 recently and I sprung a leak in my lower radiator hose. I have bled the cooling system several times according to my haynes manual and when I replaced thermoswitch a coolant came out so I know it's getting to the switch.

doctorbee - I have to keep my AC on because that's the only way my car won't overheat. It turns both fans on.

 

Ok, you may not like this but I'm wondering if you might have a head gasket issue?

Can you do a compression test and or leak down test?

 

Have never done one before but I guess I could buy a compression test kit from autozone right? Is it hard to do?

 

I put my old P1E ECU from a honda odyssey back in because I have the F22B6 engine. Now the fans both cut on when the temperature gauge shows slightly above half. It doesn't go up past that point though. I'm thinking that maybe the gauge is giving an incorrect reading and maybe it's actually sitting at normal? That would be the coolant temp sending unit correct? Located under the distributor?

 

The temp sender for the gauge is the "single" pin one under the dist. It can be tested as well before replacing.

 

Now I slapped my original ECU for my car back in, and I bled the system properly according to the haynes manual. I let the car idle for nearly 15 minutes before I capped off the radiator, but my fans never came on. I then drove down the freeway and came back and parked for 5 minutes. The temp gauge creeped up and right when it hit halfway the fans came on. They came on at least 4 times and the gauge never went past 1/2. Is that normal during the summertime? It was only about 85 degrees outside. Is it possible that my temperature sender is a little off?

P.S. I also want to add that if I keep my AC on the heat gauge stays at about 1/3. It never gets to halfway.

 

That's about normal. The temperature gauge isn't the most accurate instrument...

When you're driving there's plenty of air moving through the radiator. The temperature gauge will settle into it's "normal" position which is about 30% or 40% of the scale for most cars.

When you idle with the car stopped, the temperature gauge will rise noticably above normal before the fans come on. So 50% or 60% is about right. If it's not a real hot day, sometimes I've had to cover up the grille in order to get hot enough for the fans to run.

When you switch on the AC, that causes both fans to run, regardless of the coolant temperature. So that alone will keep the coolant temperature down.