1990 Honda Accord Overheating

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Hi folks,
My old Honda Accord got overheating trouble recently. Here is my finding: 1. It got overheating on the local right off freeway or a long drive at
local. 2. The radiator fan start up right after the engine is shutdown. It fail to start even the temperature gauge goes high and the engine is running. 3. Didn't pay attention to condenser fan.
My doubts: 1. Radiator fan switch is bad. But it did start after the engine is shutdown. 2. ECM sensor is bad. But I have no idea what this thing is and where it is located.
Anyone has similar problem?
Thanks
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For the record, how old's the thermostat? Is it an OEM thermostat?
www.autozone.com has a free online manual for your car. The CRX and Concerto factory service manuals at http://www.honda.co.uk/car/owner/workshop.html should have some exact instructions for testing various switches and sensors.

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Hello, I suggest that you change the thermostat and check for any leaks while the engine is running. You should also buy a repair manual for your Accord. The manual should help you to locate the parts that you mentioned. If you have never before changed a thermostat, take the car to a mechanic. If possible, watch the mechanic in order to learn how to do it. Jason
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Ivan wrote:

Short the fan's thermos witch. The fan should come on. If it doesn't, check the wiring. If it comes on, leave it shorted and see if the temperature remains normal. If it does, replace the switch. If it doesn't, there might not be any coolant running by that switch. That might be caused by a bad thermostat.
Remco
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I have some new findings now and I am more confused. 1. For switch B, which is the condense fan switch according to repair manual. This switch is closer to the front compared with switch A. No fans come up running with the engine turned on even I short it. With engine turned off, it automatically turns on the radiator fan (passenger side) when engine is hot or I short it. 2. For switch A, which is the radiator fan switch. This switch is closer to the fire wall compared with switch B. With engine turned off, no fans come up even I short it. With engine turned on, both fans come up if I short it. With engine and A/C turned on, both fans turned on or off automatically.
Is it possible that the two fans has been mistakenly switched due to installation error? I mean the radiator fan should come up when I shorted with engine on.
Thanks for all replies. The conditions are: the thermostat should be fine because the upper hose is hot. I just flushed the radiator and carefully refill with a mixture of water and coolant. And of course, the radiator is kind of dirty. I also noticed that if both fans comes up, the temperature gauge goes down really fast.
Any other diagnose ideas?
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Ivan wrote:

When you say switch A and B, do you mean relay? As far as I know, the condensor fan does not have a switch, but is controlled by a signal from the ECM. When that signal is true, both fans should run. I think there's usually a diode pack that takes care of making sure both turn on.
When the engine cooland temperature switch (the switch, not the relay) closes, it closes the contact on the radiator fan relay should close and the radiator fan should run. Have you located the coolant switch?
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Remco wrote:

Sorry about confusing the issue - forget what I just said. I found the schematic to your car at autozone.com and it has two temperature sensors A and B - that must be what you are talking about.
I'd measure the voltage across both switches and see what happens when the car warms up. They should both go from around 12V(cold) to zero (hot). If you see 12V but never zero, I'd replace that particular switch. If you never see 12V, check resistance across the switch. If it isn't shorted, you may have an issue with that fan control module or the wiring. If it is shorted, those fans should be on..
Report back with your findings. I'll bookmark the schematic. Remco
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The manual is not quite correct. Switch B is simply a secondary fan switch. It comes on at a higher engine coolant temperature, and its power feed is controlled by the timer unit.

That switch gets its power from the ignition switch. If the ignition is off, it won't have power.

Do they come on *before* the engine temperature gauge starts to climb?

The thermostat would be fine if the LOWER hose was hot! This isn't a 1976 Dodge. The thermostat is in the LOWER hose. The LOWER hose will not get hot until the thermostat opens. And neither will the bottom of the rad.
How even is the temperature of the radiator core with the engine starting to overheat?

Inside or outside?
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Hi TeGGeR,
Thanks for your clarification. So I have to take the timer unit into consideration when I diagnose the problem. Here is the answer to some of your question: 1. Do they come on *before* the engine temperature gauge starts to climb? A> It definitely come on before the gauge reach the normal operation temperature. I'll test to see if it come on when it is cold started. 2. Inside or outside? A> Both Inside and outside, I used a power washer cleaned the outside, but the inside still looks bad.
Question to you: Where is the timer unit located or is it the ECM? How is it supposed to work?
Thanks, Ivan
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Hi TeGGeR,
One more answer to your question: I noticed that both upper and lower hoses are hot. When the engine starts, the radiator and upper hose get hot a whole lot faster than the lower hose. I also noticed that the old upper hose get swollen really big before I replaced it. The new upper hose has the tendency to become swollen. Thanks for your analysis.
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Ohhhh, that's not good... If the upper hose is swollen, then you've got excessive pressure in there. How old is the rad cap? Have you tried replacing it?
Sounds like you probably have nothing wrong with your timer unit, but more mundane problems with a dirty system or bad thermostat.
If you still want to find the timer, it's here: http://www.tegger.com/hondafaq/misc/89-91_Accord_underdash_relays.pdf
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The cap is a new one and I am in the process to replace the radiator. The problem is I rarely saw the coolant flow to the reserve bottle. Let's suppose that the system is dirty and flow really slow, the coolant still still need to flow to the bottle if it is really hot. I'll see if replacing the radiator make any sense or not. I'll post the result here.
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Replace the thermostat first.
Check my other reply (to Jim Yanik).
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excessive pressure in the cooling system could also be a bad cylinder head gasket.
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>>

Correct. And at that point you'd see the reservoir level climb up high, then not drop back down again, and the rad level would decline at the same time.
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That doesn't make a lot of sense to me - I would think the cap would still bypass the pressure - but it is widely reported so somehow it must be true.
Mike
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I asked a garage to replace the thermostat when they replaced the broken water pump (I mean it was broken and water leaked out through the hole). If they really did it, my thermostat is only two months old. The garage guys just can't figure out the problem and asked me replace everything except the engine.
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Ivan wrote:

OEM Honda is recommended. Maybe they put in an aftermarket thermostat?
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When I checked thermostats at PepBoys,all they had was 180 degF ones,and my Integra GSR uses a 195 degF TS. I bought one from the Acura dealership.
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The thermostat they replaced got to be an aftermarket one. The radiator running in this car is also a aftermarket product. I am thinking to get all these corrected.
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