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Old 03-04-2011, 01:31 AM   #1
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Default Overheating 1.6L Stock not boosted

Let's get the basics out of the way. Used the search? Check.

Otherwise, sorry for the book... I just wanted to share all that I DO know about it.

Okay, so even though I'm not boosted there is enough knowledge here that I'd rather get feedback, and thoroughly abused/made fun of for any laziness and procrastination on my part... what's not to like? Now, more details that I could ever need on the issue.

Car History: 1991, does have the short nose but doesn't seem to have had an issue to date. Got it with about 165k miles 18 months ago. No knowledge of exact mileage of last waterpump timing change –previous owner gave the typical "not that long ago" kind of answer.

Last winter I picked up a hint of that familiar anti-freeze smell with the heat on. Never found leaks, never had any other issues other than that faint smell.

** side note, I had no planned on driving it with this stock 1.6L in it this long, so I didn't do what I should have... replace both.

Searches tell me that like most 1.6L, this is what my temp has always looked like.




A few weeks ago, I took advantage of a large parking parking lot and some rare Texas snow and ice. Lots of high revs, very little forward motion. Wasn't long before I decided to look down at a gauge other than the tach... time to shut it down, as the gauge looked a lot like this




The car seemed normal. Few days and a few degrees later, and my freeway drives of 70MPH looked like normal temps, but stoplights and low speeds were very different.




Did the typical checks, fan running, fluid wet and plentiful, cap on proper and appears to be working, no visible leaks.

As of today, 70-75 degrees, freeway temps:



As of today, 70-75 degrees, stoplights look like:




At lights when it's hot, revving (3k or so) for 8-10 seconds brings the temp down.




Same hot scenario, turning the heat on full blast drops the temp, as does running the A/C (get that second fan)




Doing both heat full with the A/C compressor on at freeway speed, brings me back down to 12 o'clock.

___________________________

My basic knowledge tells me that water is not circulating the system as well as it should. It's as full as it should be, although I don't know the original contents of the system, a 50/50 mix was added back in. The fact that the heater helps tells me the water is at least flowing some, and the A/C cooling what's in the radiator supports that as well. But if it's getting that hot in low rev conditions, and only slightly warm in higher rev conditions, am I right in assuming low circulation?

Beyond that, will a simple stuck thermostat condition (partial or whatever) give me this, or am I just looking at a faulty water pump at this point? I know that a replacement of the belt and water pump must be on the agenda, but as I've never done it AND I have that pesky short nose thing that I've been told is easy to screw up if I don't know any better... it's obvious why I'm looking for every solution between ignoring it and doing what has to be done.

Aaaaaand begin.
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Old 03-04-2011, 02:34 AM   #2
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My cousin's miata did the same thing a couple weeks ago. He replaced his thermostat and bam, problem taken care of

This seems very much like his issue, and since thermostats are cheap, go get one
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Old 03-04-2011, 02:55 AM   #3
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The OE thermostat is dual-temp. It might be that only the smaller secondary thermostat is opening.
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Old 03-04-2011, 05:30 AM   #4
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While you are changing the thermostat, flush the system real well and add a true 50/50 mix
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Old 03-04-2011, 12:43 PM   #5
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I read this first thing this morning and said, 'ah excellent... I'm not way off thinking a thermostat change could fix it'.

Drove in with slightly higher than the above illustrated temps, pulled into the parking garage with them even higher. Back into my space walked out to the front of the car to find a little drip-drip-drip trail leading the center front of the engine bay and a final saucer-sized puddle right under it.

Crap.


Anyone else thing my hope that it's a pressure caused leak related to a mostly closed (or more) thermostat is wishful thinking? I'm going to start peaking around with a flashlight at lunch, but I'm less than optimistic.

Thanks for reading all of that above, and giving me feedback guys.
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Old 03-04-2011, 12:50 PM   #6
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it could be anything. that fact that you are driving on it is silly.

my advice would be: find the leak and fix it.

If your cap is working correctly it should relive excess pressure before things explode.
If your fans were working correctly they'd cool the temps.
If your thermostat was working it would open to allow the coolant to flow into the rad.

If you have a leak somewhere, pressure cannot increase and you will overheat.
If your thermostat is broke, pressure AND temps will increase and eventually things will burst.
If your fans are dead, typically driving around at high speeds brings temps back down.

You can typically smell coolant before finding the leak...you are just skating on thin ice, that has cracked, and smells like poop.
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Old 03-04-2011, 12:51 PM   #7
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If it's the original radiator, all this excessive heat could have destroyed the plastic end tanks.
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Old 03-04-2011, 01:00 PM   #8
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Sounds like the cursed water plug: http://www.miata.net/garage/waterplug.html




Like Braineak said, stop driving it. If that needle moves at all past the 11:30 position it's too hot and something is wrong. There are some pictures on miata.net that show the temperatures and position of the needle. There is a ridiculous range, something like 160-220, before that thing even budges.
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Old 03-04-2011, 01:03 PM   #9
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it moves to 12 o clock around 215°F
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Old 03-04-2011, 01:09 PM   #10
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I can't find the pictures now, maybe I'm mistaken.

I did find this graph though which seems even more drastic than I was thinking:



At any rate, if my gauge hits 215 I'm looking for a place to pull over. I blew a headgasket once and don't intend to repeat that performance.
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Old 03-04-2011, 01:12 PM   #11
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the 1.6L CLT gauge reacts differently/better.
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Old 03-04-2011, 02:05 PM   #12
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Is there a solid test for the cap? I don't know that it was working to begin with since in the history part of the OP I mentioned that when it overheated while playing on the ice, it popped the reservoir hose off and shot all of the steam out there. That to me, indicates that pressure was allowed to build up possibly more than it should have in the beginning... any truth to that?

The fans I've verified to be working throughout the process, regardless of the fact that any time I were to speed up the temps would go down. Electric fans are pretty much pass/fail, correct?

I've been able to smell coolant ever so slightly for 35k miles, and have never found a leak, or had an overheating issue... so that early indicator wasn't much help in this case. The car will have to be driven home today regardless... I'm going to make sure the system has fluid in it, get it to operating temp and see if I can identify a point of origin for the leak. I'll also check the radiator hoses for pressure/heat to see if it seems like flow is weak.

___

So, is the water pump on this car pretty much work/not work? Or is there a point where some internal pieces get worn to the point that they are less effective and cause circulation issues? Replacement needs to be in the future, but at 202k miles, I'd like to be putting more into it than a belt and a water pump.
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Old 03-04-2011, 02:09 PM   #13
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a new cap is $5 at autozone. that's how you check it
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Old 03-04-2011, 02:14 PM   #14
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Easy enough. I thought I read in another thread that the failure rate on random aftermarket caps was so random, that it may not provide a good test. —Maybe that was a different part.
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Old 03-04-2011, 03:59 PM   #15
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New cap, old results. At least I know it's not likely the cap. If I keep the heat and A/C running the system didn't crawl much about 12 under any circumstances that I threw at it. I was evaluating the system right after the cap in stoplight conditions, and it was solid at just over the 11 mark, but then suddenly made it's move and took off to 1 before the A/C and heat brought me back down to 12. 30-40MPH with stoplights at 12, Freeway 65MPH under 12. I suppose whatever the issue is, it's not a total failure for the part in question.

No leaks the whole time I was out, I'm sure the conditions could be recreated if it got very hot, but I don't know where it came from. Suppose it's possible that that reservoir overflowed and that was the results of the drain tube, but I highly doubt it, as the leak stopped the moment the engine stopped.

Bought the thermostat while at Autozone, I'll evaluate again after I put it on tomorrow.
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Old 03-04-2011, 04:04 PM   #16
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that's because running the heater allows all the heat that's building up in the coolant escape through the heat exchanger and through your vents onto your pretty face...

thermostat would be the next step, but if you had a puddle this morning fluid is obviously able to leak somewhere....you should the idle until the fans come on and really take very close look at anywhere coolant can leak. a simple pinhole leak might not show itself until you are under rpms, and can cause your issue...squeeze the hoses.

dont let it sit too long and overheat and kill your head gasket...
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Old 03-04-2011, 04:09 PM   #17
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Ah, I probably should have elaborated there. It sat while I looked around (with both of those items on) for 10-12 minutes and didn't budge above 12. I poked around, checked the top hose looked around the front of the motor and anywhere I could touch/see without getting my office clothes screwed and didn't see any evidence of the leak. I could not check the bottom hose however.

I knew why the heater worked... that's what actually led me to start doing it. I kept bringing it up, because I'm not aware of the route, and if limited flow would net me as much heat dissipation as it's supposed to when I run the heater. –But it [heater] is getting plenty warm.

The system is full of coolant/water (mix jug in the car), so I'll just take it home, jump on the thermostat in the AM and start evaluating again.


Thanks and everyone else who's given feedback.
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Old 03-04-2011, 07:56 PM   #18
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As I drive home... Noticing that the main fan is only operating with the Aux fan; on at the same time and off at the same time. The gauge is at 11-12... Shouldnt the main fan be staying on?
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Old 03-04-2011, 08:54 PM   #19
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I believe the main fan should always be spinning when the engine is running.

Last edited by Braineack; 03-04-2011 at 10:11 PM.
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Old 03-04-2011, 10:11 PM   #20
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no noob. the main fan turns on at 196*F. or when the a/c is on.
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