Overheating shutdown

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Overheating shutdown

Post  mghalpin on Wed Jul 16, 2014 7:54 am

I took my 2001 NB to Limerock yesterday for an AutoX event and in each of the first two runs (these runs are continuous laps for 10 minutes or so...) the car overheated and then stalled. Once stalled the fans would not work. Checked fuses.... all fine and once the car cooled down, fans came on and car started. Coolant level is fine and recently flushed and replaced. I also noticed a light on the dash I had never seen before. Looks like a car with a key overlaid on it. It's on the right side of the display opposite the cruise indicator.

I assume something is monitoring overheating and shutting down to prevent damage. That seems a good idea;-) But I am surprised that the fans would not still work to help cool down the engine.

Any thoughts on whats happening?

Thanks!
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Re: Overheating shutdown

Post  mike.s on Wed Jul 16, 2014 5:19 pm

Light with a key sounds like an immobilizer warning light to me.

Stalling when hot is usually associated with CAM sensor from what I've read. But. overheating is the very first thing that i would look at. How do you know it's "overheating"? Have you looked at temperature through OBD2? Did your temp gauge move up?

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Re: Overheating shutdown

Post  mghalpin on Thu Jul 17, 2014 1:29 pm

The temp gauge had moved right of center, but was not pegged. I don't see any log in OBC that indicated high temp. The OBC II code I see is PO340 which looks to be a CAM sensor as you suggested.
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Re: Overheating shutdown

Post  mike.s on Thu Jul 17, 2014 6:04 pm

I would chase teh overheating issue befere anything else. Specifically, the fake temp gauge in NB moving at all is a clear indication that the car is really overheating.

I don't say that you'll see an overheating code in OBD2. Instead, what you can do is connect some ELM327-like device to OBD2 port and look at actual engine temperature with something like TorquePro, ScanMaster, etc on your Android device.

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Re: Overheating shutdown

Post  mghalpin on Mon Jul 28, 2014 7:17 am

Thanks Mike. I flushed the coolant and replaced the cap then connected an OBD II device to Torque on my Android as you suggested. The fan fires consistently at 204 degrees which seems to be according to spec for the connection between the thermostat and the fan. It's hard to replicate the stress of continuos laps that first produced the issue, but under typical AutoX conditions all looks good. Maybe Rob would consider letting us run all timed laps continuously at the next event so I can really test ;-)
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Re: Overheating shutdown

Post  mike.s on Mon Jul 28, 2014 2:00 pm

Third gear at highway speed for about 10 minutes should replicate it pretty well, I'd think.

One strong suggestion - use OEM replacement cap, not aftermarket, if you haven't already.

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Re: Overheating shutdown

Post  mghalpin on Mon Jul 28, 2014 4:54 pm

That test was successful in producing the shutdown. I ran the car at 6000 rpm for 8 miles and while the temp was elevated, it was stable at 223. Then loss of power and the fan shut off. I waited about 10 mins, temp was down to 215 and it restarted with the fan running . the error code is the 340 power train cam position sensor error.
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Re: Overheating shutdown

Post  mike.s on Tue Jul 29, 2014 1:05 pm

Cam position sensor is a very common failure on NBs. The sensor gets overhated and either the connections fail inside or things physically move. If I'm not mistaken, it's a Hall effect sensor. If so, it relies on a gap between the magnet and the cam and if that gap changes... assorted failure modes lead to a lot of fun.

You can buy a can of compressed air and blow it on teh cam sensor if and when it shuts down next time. If teh car restarts and runs after that, you got your answer. Based on what I've read lately, it's just better and easier to spend $50 on new sensor and 2 minutes to put it in - truly one of the easiest parts to replace on a Miata.

What still concerns me is overheating. Cam position sensor will be affected by overheating. But not the other way around, I don't think.

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the end of the story....?

Post  mghalpin on Thu Oct 23, 2014 3:48 pm

well hopefully.... so after several additional incidents including a failed ride up Mt Washington (nice road to over heat on;-)) I swapped out the radiator, thermostat, cap, hoses... everything but the water pump and voila! no more overheating. I think in the end the radiator was the culprit as the flow through it seemed to be restricted.

Thanks for your help Mike!
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