Under standard driving conditions the cooling system operates normally but once I start to drive up any lengthy hill (say a kilometre or more) the car begins to overheat (temperature gauge goes from just above a quarter to 3/4) very quickly. If I turn the aircon off, the temperature slowly returns to normal even if still going uphill. If I drive the car without the aircon on, the car does not overheat regardless of operating on the flat or on hills. The problem has arisen since the weather in New Zealand has got hotter, although that might be co-incidence. (NZ is right hand drive, all distances are in kilometres and I think Accord in NZ = Acura in US).

Things I have noticed associated with the problem:
If I don't notice the temparture rise (as I said it happens quickly) my first indication is that the aircon looses its cooling effect like some sort of switch has recognised the need to automatically turn off aircon to help the engine cool itself.
If I turn the car off when it has overheated, the radiator fan comes on for several minutes after engine shutdown. I think this is what it should do to help cool the engine down.

Car Details:
Car: 1998 Honda Accord VTI-L 3.0 V6
VIN: 7A3CG1640WNVG 0066
ENG: J30A113385530
Mileage: 200,340 km

Things I have done so far:
When the problem occurs I have stopped the car, left the engine running, opened the bonnet and checked that both fans are working. No problems there, but of course I don't know if one or both fans momentarily did not work (causing overheat) then started again so that by the time I have stopped the car and checked under the bonnet that are happily spinning!. Due to the potential of expensive engine damage I am reluctant to continue to operate the car in the overheated condition just to just see if by chance the engine will cool again all by itself as a result of intermittent fan operation.
As explained above, the radiator fan also comes on after engine shutdown when the motor is overheated. In addition, I have noted the aircon fan starting with engine start (and aircon on). It seems the fans are both working as expected.
I have checked the coolant level at cold. Coolant is 50/50 antifreeze and has been relpaced recently. I can confirm the radiator is full to the neck and the header tank has fluid to the minimum mark. There are no leaks and the coolant level remained constant (no top ups required) before and after its replacement.
I have checked the radiator and condensor fins and there are no obvious signs of external blockage or damage that might affect cooling.
I have replaced the thermostat with an OEM part and have also replaced the water pump. I have noted the condition of the antifreeze which was very good and also the cleanliness of the internal passages at the water pump, thermstat and radiator filler neck entrances. There are no signs of any corrosion. I suppose there could still be an internal blockage but it seems unlikely given the shiny/clean nature of all the interanl passages I can see.

I have replaced the radiator cap with an OEM part.
I have replaced the fan control module and have also replaced the radiator and condensor fan relays.
The only items left to replace are the temperature control switches A and B and the engine coolant temperature (ECT) sensor although I think the ECT sensor is unlikley to be the culprit. I say this because the temperature gauge indications of engine overheating, seem to be supported by the fan going on after engine shutdown. The check engine light has not come on either which might be expected if the sensor was faulty. Am I wrong?

If the problem is with one of the temp control switches, which one is it likely to be? A or B and which one is A and which one is B. I don't want to replace more needless parts. Am I on the right track or is the overheating simply a sympton of something a miss in the aircon system? The engine remains at normal operating temparture without the aircon on so could this in fact be a problem with the aircon system for eg, might there be an internal blocakge in the condensor? Does refrigerant block condensor passages?

Any help would be most appreciated.

Regards

Terry

 

I guess that I have one question. Was the overheating the reason that you replaced the water pump/thermostat? Or did the car start to overheat once you replaced those items by changing the timing belt?

The A/C adds extra load to the system, so the fans run to help cool the engine.

One possibility is that air is trapped in the system. When you fill the radiator, open the air bleed nipple on top of the thermostat housing. Fill the radiator and allow all of the air to spit out. Close the valve when a steady stream of coolant comes out. Top off the radiator.

A clogged radiator could cause the problem. Try the radiator flush stuff that you can pick up at a parts store.

A faulty thermostat (although it is new) can be identified if one radiator hose is hot while the other one is significantly cooler.

 

Thanks PAhonda for your response Yea, I see where your coming from. Did I screw up the timing when I replaced the cam belt? I'm pretty sure I haven't as the problem existed before I stripped it down and the car's running like a charm now (notwithstanding the overheating problem).

So far as air trapped in the system is concerned, as I said the problem existed before I drained the coolant. Nevertheless, I am familiar with the procedure for ensuring trapped air is released although the funny thing is there does not appear to be any bleed air nipple fitted to the V6's like there is to the four cyl's? The Honda Care manual that came with car outlines the exact procedure you gave for the 4 cyl but is quiet with regards to the v6. ( The handbook covers both types). For the V6 it simply says to fill it up and squeeze the bottom radiator hose to expel air?

I received some other helpful advice to make sure there were no kinks in the radiator hoses. I am really only left with flushing (or replacing) the radiator and /or replacing the fan switches A and/or B. Can you tell me anything about those switches? What do they do, where are they located? I'm pretty sure one is near the thermostat but where is the other one and which one is which?


Regards

Terry

 

For the 4-cyl 1998 Accord, there is only one fan switch, no A & B switches. I imagine that part is the same for the V-6.

Earlier Accords, one fan switch was responsible for switching the fan while the engine is running. The other switch was responsible for the fan running after you turn off the engine.

 

Assuming you are correct, the car is overheating w/ cooling fans functioning. This doesn't leave a lot of causes, and all seem unlikely:

1) partial radiator blockage (use an IR temp gun to look for cool spots in radiator (no flow). May require releasing radiator from restraints to access radiator for temp shoots.

2) Faulty thermostat- unlikely, but you only have unlikely causes. Replace thermostat or remove and check for opening in a pan of boiling water.

3) Faulty Engine Coolant Temp Sensor - it could be off enough to show high temp when none exists. OEM manual necessary to check calibration, or replace sensor.

4) Possible faulty Thermoswitch A - Thermoswitch A should come on enabling cooling fans about 195F (assuming V6 is same as IL4). A bad switch might not come on until temps are high, causing slight overheat. Check thermoswitch by holding in heated water to see if contacts close near correct temp. They should close shorty before water begins to boil or use temp gauge.

5) Internal coolant passage blockage - Remove thermostat and flush both ways and check for flow.

6) Internal upper/lower radiator hose defect (loose flap of hose liner) causing blockage of hose. Remove hoses and inspect. I've heard of this but never seen it.

7) Worn/corroded water pump not circulating adequate coolant - Tough to check w/o removing water pump. Very unlikely w/ good coolant service. I think this would be my last check. Hopefully, something else will turn up. It might be possible to run engine, release a hose, and dump cooling flow into a bucket to check for flow rate. Replenish w/ new tap water. I don't know what spec flow rate is req'd.

good luck

 

Thanks JimBlake and Texas Honda.

I think your number one suggestion (partial radiator blockage) might be the culprit. While I had indicated in my thread that I had checked for external blockages, I had only done so by looking down through the small gap between the condensor and the radiatior (you can't even get your fingers down there). I looked for obvious blockage such as a piece of newspaper, plastic bag or a collection of leaves etc. Everything seemed ok. But I have now taken a real close look and noticed dark patches on about 30-40 percent of the radiator. I think there may be some insects etc in those areas and will take the radiator out this weekend to confirm. I'll let you know how I get on but it quietly hopeful a solution is at hand!

Thanks guys and fingers crossed!

Regards

Terry

 

We're talking about blockage inside the water passages of the radiator. But obstructed air flow is another problem that you can check out (rule out).

If the water flow is obstructed by something like lime/scale buildup inside the radiator, then the water flow is small. Then the water has plenty of time to cool down in the radiator, so the bottom hose is cool. But the flow is too small to cool the engine.

Sometimes you can clean it out with radiator flush products, but sometimes it's accompanied by corrosion. Then it's just gonna start leaking when you clean out the scale.

 

I've cleaned radiator by releasing the upper radiator guides allowing the radiator w/ fans to be pushed rearward slightly while sitting in lower supports. This may allow an adequate look to check for radiator external blockage.

good luck

 

Thanks for your further suggestions guys.

I'm reasonably confident that the inner passages of the radiator are ok...well...as confident as you can be about something you can't see. I say this because replacement of the thermostat and the water pump and the subsequent dumping of the coolant gave me a great opportunity to look at portions of the internal coolant passages at points either end of the motor and at the top of the radiator. Those passages all looked like new and were all shiny. The coolant was clear and exhibited no signs of cloudiness, rust or suspended particles. Of course we can never rule out the possibility of blocked internal passages (perhaps through some mechanical failure of the radiator core?) but the evidence to date doesn't seem to support it. Having said that, if I don't reveal any significant blockage in the radiator fins this weekend I may be eating some humble pie while listening to a duet of 'we told you so' lol.

Thanks also for your suggesting about partially removing the radiator attachements and leaning it backwards. It won't hurt to do that and might be quite revealing. It'll give me an opportunity to take a proper look at the area so I can determine whether I need to take the job any further.

Thanks again and have a good weekend guys.

Regards

Terry

 

I APOLOGIZE for bringing this back from the dead but, i need help..i'm in the same situation here.

i'm a newbie to the forum seeking guidance.
Auto 97 accord SE with about 60k miles on the MOTOR.
recently this problem came up..
things i had mechanic did:
change t-stat, flush system, replace temp gauge sender unit <<temp gauge needle didn't move at all before..now it works fine..
EGR plate clean out to clear p1300 code
now on to the problem...

idle fine, temp is at 219 degree <<mechanic measure with his temp gun..found no problem but he DIDN'T DRIVE the car, will call him tomorrow..
car warm up good, drive for awhile, turn ON A/C and needle start climbing past 1/2 way mark but don't not peak out..turn OFF a/c and it go back to normal..

what else do i need to do? i've read through 13pages of search result for this and come up with nothing conclusive..some suggest faulty t-stat, check for faulty temp fan switch..clogged radiator..radiator were FLUSH when new t-stat replace, so not it..system got hot air so there's no air in the system..

so recap
Idle = ok
30mins drive with a/c on = overheat
a/c off = normal

no cel, mil, or anything like that..

thanks