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-   -   Strange Overheating problem with my OHC (https://www.team-bhp.com/forum/technical-stuff/26532-strange-overheating-problem-my-ohc.html)

I have been experiencing a wierd overheating problem with my 99 OHC. When I am driving the car, the temp is normal, however, If i get stuck in a traffic jam, or slow moving traffic, the Temp gauge starts to go up quite fast.

It goes up near the red line (~1-2 mm below it) in say about 3 - 4 minutes. Once the car is in motion though, the needle gradually comes back to normal. The fan comes on normally when the temp is rising.

Now the interesting part. Even when the car is stationary, and the needle is nearing the red part of the Temp gauge, if i switch on the AC, the needle comes back to normal (~2 mm below the half way mark) within a couple of minutes and stays there. :confused:

I have had the car serviced + water washed with a high pressure hose and the radiator is not clogged, got the coolant changed a couple of weeks back. There is absolutely no problems of overheating when the car is in motion. Have undertaken quite a few long drives without any problems.

What do you reckon the problem could be.

I am not an expert by any means but since I faced exactly the same problem with my Mazda MX-6 in US, I can share the details of that. May be the problem is same here.

In my case, radiator fan was not working. When car is in motion, the fresh air helps cool the radiator. Also when I switched on the A/C, compressor fan helped cool radiator because it was located close to it.

My apologies if the above doesn't make sense here at all.

Radiator fan is not working, check fuse first, then move on to thermostat switch that switches the fan ON, and then the actual fan. Also since you mentioned washing just check all the wiring couplers are in tact and in place, might be a simple lose connection in one of them.

I dont remember if the OHC had 2 separate fans, when you switch ac on, the ac fan is cooling (if separate fans) or the signal from ac is switching on the single fan, then its fuse/wiring or thermostat switch for sure.

This is exactly what I had in mind to say from my experience with my old M800 a decade ago. So, dont worry. It does make sense. :)

Thanks a ton all, will get the fan checked.

As people have said, its the radiator fan.

Since you mention you got your car serviced and washed, its quite possible that its a loose connection or a faulty relay.

I would stand around while they try and fix your car (or even just go to a roadside mech and tell him to check it out first) just to make sure they dont try and charge you for a new fan or something when its just a blown relay.

cya
R

The OHC does have 2 fans & this seems to be the radiator fan problem. And like Rehaan mentioned, apart from the fuse & couplers, please remember to check the Relay too.

As pointed out by many, the radiator fan seems to be the first suspect.

Could this problem arise if the engine idling rpm without AC is too low? If I am not mistaken, the revs increase when the AC comes on. So when you switch on the AC, the idling rpm increases to the correct level and the problem disappears.

I am guessing that the coolant flow will be insufficient if the idling rpm is too low. What do the experts have to say on this theory?

More generally, apart from radiator fan malfunctioning, the problem could also be due to insufficient coolant flow when idling without AC. One reason, as I mentioned above, could be that the idling itelf is incorrectly set and the rpm is below normal. Secondly, I am wondering if the thermostat that controls the coolant flow could malfunction when the engine rpm goes down to a sufficiently low level (as in idling without AC) and fail to open enough, restricting the coolant flow. Could be a combination of these two problems.

Stupid question, when we switch on the AC, do Both the fans come on ?
I just started up the car, warmed it up and when it was idling switched on the a/c to figure out which was the AC fan. Both the fans came on simultaneously. Is that normal, or is there something wrong with the wiring.

This is normal and since we know that the fans are working you will need to check the thermostat switch which triggers the functioning of the first fan.

Any idea how much the thermostat switch would cost, should i need to replace it ?

I have no idea, but I don't think it should be very expensive.

You should be able to check if the radiator fan comes on when the temperature goes up upon idling after driving for some time. If so the thermostatic switch is doing its job.

There is also a thermostat (which is basically a valve) that controls the coolant flow by opening or closing depending on the coolant temperature. It seems to functioning well in your case while the car is running. I have no idea if there is any reason to suspect failure of the thermostat at idling rpm; could be possible, although I doubt it.

I think if the radiator fan is fine, you should take the car to an authorized Honda dealer and get it checked in detail. If the problem is with low coolant flow at idling speed without AC, a scan of the ECU and engine should reveal it.

Edit. Here is a link to a web forum discussing the same problem:

b16 overheating at idle - beyond.ca car forums community for automotive enthusiasts

Quoting a couple of posts from this link:

@ rks Thanks a ton buddy, really appreciate it.