Overheating troubleshooting

9002 Views 24 Replies 6 Participants Last post by Charles, Oct 16, 2005

Charles

Discussion Starter · Oct 12, 2005

Problem:
Car overheats when idling after driving awhile in hot weather. Never on the highway.

History:

Car was in a front end collision and repaired in 2004. New condensor, radiator (replaced with all metal dual core), and fans (Spal). Because of the extra thickness of the radiator and the Kamikazi header, the fan in front of the header is thinner than the other one. Original coolant was Honda but shop later used Prestone.

Diagnosis:

I think there are multiple issues.

1) Both fans come on with AC. Will still overheat if revved at 2500 - 3500 for a few minutes even with the new cool weather here (75F). Does not appear to overheat at idle with AC on but not sure.

2) Neither fan will come on without AC.

3) If AC is on and radiator fan is pulled from fuse box under hood, only one fan cuts off.

4) Coolant is flowing through the radiator. Thermostat seems fine and is less than 2 years old.

5) Have not tested fan relay yet. No voltmeter.

Possible issues:

1) Bad fan relay.

2) Improper coolant.

3) Bad wiring. Wiring looks ghetto. Stupid shop could have wired incorrectly.

4) System not bled. On a ZC, it looks like a pain to get to. What do you guys use -- a ratchet extension?

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1 - 20 of 25 Posts

jfrolang

· #2 · Oct 12, 2005

I'm not really a cooling system expert, but one thing that grabbed my attention was this right here:

Charles said:
If AC is on and radiator fan is pulled from fuse box under hood, only one fan cuts off.

Which fan goes off? I'm guessing radiator fan of course since that's what the fuse is for, but you also said the wiring could be wrong.

Charles

Discussion Starter · #3 · Oct 12, 2005

The one in front of the header.

stick

· #4 · Oct 12, 2005

As far as I know, both fans are supposed to go on when A/C is on. It sounds like you have a bad thermoswitch on the back of the block. It's never turning the Rad fan on when the coolant is getting too hot. You might want to test that as a starting point.

Charles

Discussion Starter · #5 · Oct 12, 2005

Both fans do come on with the AC. Neither comes on without the AC on.

Does the thermoswitch directly turn on the fan or does it flip the relay on the passenger side near the from.

stick

· #6 · Oct 12, 2005

I think it sents a signal to the ECU and the ECU turns the Rad fan on. The relays that are mounted up by the headlights are for the A/C system only.

bittles110

· #7 · Oct 12, 2005

stickershop said:
As far as I know, both fans are supposed to go on when A/C is on. It sounds like you have a bad thermoswitch on the back of the block. It's never turning the Rad fan on when the coolant is getting too hot. You might want to test that as a starting point.

I concur. When I turn my A/C on, both fans come on, no matter what the temp. With A/C off however, the radiator fan (and possibly also the condenser fan) will kick on and off to keep temps down. Check the thermoswitch.

Charles

Discussion Starter · #8 · Oct 12, 2005

Which one is the AC fan? And could you check to see if both of yours come on with the thermoswitch or just one?

How much and what is the part number for a Thermoswitch?

bittles110

· #9 · Oct 12, 2005

The A/C fan is the one on the drivers side. I think it's a bit smaller than the stock radiator fan as well. I can't check it right now, I just got home and it'll have to cool. But once it does, I'll check for you.

As for the thermoswitch... I'm not sure. I doubt they would be more than ten bucks, and most auto parts stores should carry them.

Good luck!

Charles

Discussion Starter · #10 · Oct 12, 2005

If I yank the fuse in the fuse box, only the driver's side fan goes out. I guess I will look into replacing the thermoswitch. Thanks.

stick

· #11 · Oct 12, 2005

It's number 22 on this diagram (near the oil pressure switch). It turns the rad fan on and off at the designated temperature.

http://www.hondaautomotiveparts.com/aut ... CORD-CLAMP

According to the factory service manual, this switch makes a connection when the temperature exceeds 191-197 degress F. (88.5 - 91.5 celcius).

According to the electrical diagrams, the ECU has nothing to do with the operation of the Radiator Fan. (my previous post was incorrect in this respect).

The ECU has it's own temperature sensor below the distributor that allows it to adjust fuel maps according to operating temperature. There is also another temperature sending unit beside it for the dash temperature gauge. These two have nothing to do with the Rad fan circuit.

Charles

Discussion Starter · #12 · Oct 12, 2005

I have a ZC. Different?

stick

· #13 · Oct 12, 2005

Charles said:
I have a ZC. Different?

Hmmm... you'll have to check thezcr.com for that info. I would guess that it's the same part, but you better double check.

Charles

Discussion Starter · #14 · Oct 12, 2005

I have posted there as well.

bittles110

· #15 · Oct 13, 2005

The A/C fan comes on when the radiator fan comes on, even with the A/C off. I fired it up and let her sit for 10 minutes, waiting for the fan to some on. Even after a few minutes after the guage read a little below half, it took 5 minutes of idling at 70* ambient before it would come on. I dunno what that means to you, but there ya be.

stick

· #16 · Oct 13, 2005

Another thought...you said your car is overheating even when both of the fans are on. How's the waterpump? What's the coolant mixture ratio? (should be max 50/50 antifreeze and water). Is the car running rich? (could lead to overheating).

Charles

Discussion Starter · #17 · Oct 13, 2005

So it sounds like if one has AC, both fans come on if the AC is turned on or the temp rises sufficiently. Must be the thermoswitch. I will test it tomorrow.

Charles

Discussion Starter · #18 · Oct 15, 2005

I can't get to the dang thermoswitch. Well, I can get to it but I can't see it and can't unplug it. I figured I would take a paperclip to the plug and if the fans come on it would let me know the switch was bad.

So what is the plug like? I thought I felt a small tab but could not release it by pressing.

shorte

· #19 · Oct 15, 2005

It should have a black hood thing covering it, it's 2 seperate individule plugs.
above the oil filter, sorta.
It is a bitch if the black thing is in good cond.

Charles

Discussion Starter · #20 · Oct 15, 2005

The black hood thing has deteriorated and slides right back on the wires. So once that is pulled back it is just two blade connectors?

1 - 20 of 25 Posts

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