Erratic Coolant Temps, Befuddled
#1
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Hello Group, bet you've never seen an issue like this one!!!!
Been fighting erratic ECU temps for quite a while. Replaced the ECU temp sender, dealer part over a year ago, replaced any hoses that looked questionable, new cap, thermostat, coolant re-route w/ remote thermostat (949), flushed system and heater core, nice flow and no garbage. Holds pressure. Stock 1.6, 12lbs Boost, 177550 mi on the clock. Checked the High Flo CAT, can see all the way through. Where head meets the block front and rear, hot side is damp/wet and have seen tiny bubbles at those two points once. Do frequently have quite a bit of moisture out the tail pipe. Plugs have good color. No water in oil or vice versa. Temp Gauge never moves past a little before the 12 o'clock position. Leak down test good, runs absolutely beautiful when ECU temps hold steady.
Last straw chosen was a coolant flush. So after the flush, refilled, burped real good until good flow seen in radiator neck. While still runnin, put cap on, complete cool down, then highway test drive @ ++75 mph for an hour, temps held @ 88 and 90c steady, beautiful. Got off the highway, temps slowly start going berserk. 88, 106, 97, 88, 109, in a scan (fast) mode. Car becomes totally UN driveable. Park the car, no percolating heard, but I figure there must be air in the system even though I hear no percolating.
Next day, car is always fine through warm up (temps steady). Go to junk yard looking for radiator necks, (cause I think the remote thermostat is too far from the block), temps hold steady, and while I'm scroungin she'll cool off, and I can burp her again before heading home. Cap off, idle 30 min, no big burp, but some overflow until the thermo opened. Erratic all the way home (highway). Really got nasty once off the highway.
I'm lost??
Been fighting erratic ECU temps for quite a while. Replaced the ECU temp sender, dealer part over a year ago, replaced any hoses that looked questionable, new cap, thermostat, coolant re-route w/ remote thermostat (949), flushed system and heater core, nice flow and no garbage. Holds pressure. Stock 1.6, 12lbs Boost, 177550 mi on the clock. Checked the High Flo CAT, can see all the way through. Where head meets the block front and rear, hot side is damp/wet and have seen tiny bubbles at those two points once. Do frequently have quite a bit of moisture out the tail pipe. Plugs have good color. No water in oil or vice versa. Temp Gauge never moves past a little before the 12 o'clock position. Leak down test good, runs absolutely beautiful when ECU temps hold steady.
Last straw chosen was a coolant flush. So after the flush, refilled, burped real good until good flow seen in radiator neck. While still runnin, put cap on, complete cool down, then highway test drive @ ++75 mph for an hour, temps held @ 88 and 90c steady, beautiful. Got off the highway, temps slowly start going berserk. 88, 106, 97, 88, 109, in a scan (fast) mode. Car becomes totally UN driveable. Park the car, no percolating heard, but I figure there must be air in the system even though I hear no percolating.
Next day, car is always fine through warm up (temps steady). Go to junk yard looking for radiator necks, (cause I think the remote thermostat is too far from the block), temps hold steady, and while I'm scroungin she'll cool off, and I can burp her again before heading home. Cap off, idle 30 min, no big burp, but some overflow until the thermo opened. Erratic all the way home (highway). Really got nasty once off the highway.
I'm lost??
Last edited by yosimite; 03-24-2010 at 03:16 PM.
#2
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I'm sorry but I am having a hard time understanding what is exactly going on in your thread. But which coolant sensor did you replace? The one on the front or the rear of the motor?
Also, if you want to make sure you bleed the system properly, get a coolant fill bucket like this:
![](http://ww2.justanswer.com/uploads/FixUrNissan/2009-06-23_013256_fill_rad.jpg)
You basically keep the bucket filled with coolant and run the car until the thermostat opens. It is the highest point on the car, and it's filled with coolant so air is immediately replaced.
Also, if you want to make sure you bleed the system properly, get a coolant fill bucket like this:
![](http://ww2.justanswer.com/uploads/FixUrNissan/2009-06-23_013256_fill_rad.jpg)
You basically keep the bucket filled with coolant and run the car until the thermostat opens. It is the highest point on the car, and it's filled with coolant so air is immediately replaced.
#3
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Sorry, better than a couple years on and off messin with this issue. Problem is erratic ECU Temps. Which sensor replaced, rear ECU temp sensor. Also replaced little coolant plug at the rear of the head. I like that coolant bucket. I've been tryin to figure out how to do what it is designed to do. (controllin the over flow until the thermostat opens) So long story short, I suspected the head gasket, plugged cat, plugged heater core, on and on and on. Now I'm back to trapped air in the system. Not aware of, or ever heard of, or ever needed the burping bucket, so I'm off to get one. You definetly pegged what I was looking for!!!! Still kinda suspect the head gasket, but really want to eliminate all BS before taking that head off. Thanks.
#4
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Sorry, better than a couple years on and off messin with this issue. Problem is erratic ECU Temps. Which sensor replaced, rear ECU temp sensor. Also replaced little coolant plug at the rear of the head. I like that coolant bucket. I've been tryin to figure out how to do what it is designed to do. (controllin the over flow until the thermostat opens) So long story short, I suspected the head gasket, plugged cat, plugged heater core, on and on and on. Now I'm back to trapped air in the system. Not aware of, or ever heard of, or ever needed the burping bucket, so I'm off to get one. You definetly pegged what I was looking for!!!! Still kinda suspect the head gasket, but really want to eliminate all BS before taking that head off. Thanks.
#6
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dustinb, as soon as I saw the item you passed along, I imediately thought, that tool is cool. Went down to the local NAPA, the associate was not familiar with it. He found two in stock. He and I were examining it like we just found a gold coin buried in the sand. So got the tool, let the car cycle at least five times, got air every time. I was suprised how many times it cycled and produced air. The third and subsequent cycles produced much smaller amounts though. The tool is effective. After the fifth cycle, buttoned her up and took her down the highway. Temps held steady, at 88c goin north, and 90c commin back south. Got off the highway, temps floated around a bit, but not near as bad, pre bucket. I think there is still air in there. Gotta make quick run to the left coast, so was not able to give it another go. Huge improvement. Bucket works perfectly!!!
Thanks again for the suggestion!!!
![Biggthumpup](https://www.miataturbo.net/images/smilies/biggthumpup.gif)
Last edited by yosimite; 03-24-2010 at 11:58 PM.
#7
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saboteur, Old coolant had a serious rust color to it. I'll find how quick new coolant turns color once I get back from a quick trip to the left coast and get to run her. Does not push coolant into the overflow tank. I've been suspecting the head gasket, but leak-down test showed all good. Cylinders 1-4, 14%, 15%, 15%, 10%. Appreciate your interest.
#10
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Got a chance to do another bleed of the coolant system. All fresh coolant after the flush. Coolant's getting a lot of a rusty substance really quick. No matter how many cycles the thermostat goes through, still get air burps. Not pushing coolant into the reservoir though or, maybe such a small amount I can't tell. So after letting her cycle at least ten times, took her out for a run, temps held steady for the first 30 miles or so, then the temps started going all over the place. I think I have, what you had...
#11
![Default](https://www.miataturbo.net/images/icons/icon1.gif)
Got a chance to do another bleed of the coolant system. All fresh coolant after the flush. Coolant's getting a lot of a rusty substance really quick. No matter how many cycles the thermostat goes through, still get air burps. Not pushing coolant into the reservoir though or, maybe such a small amount I can't tell. So after letting her cycle at least ten times, took her out for a run, temps held steady for the first 30 miles or so, then the temps started going all over the place. I think I have, what you had...
#15
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My cooling system runs backwards, so water enters the radiator from the bottom. I simply unplugged the radiator drain, and forced water from the filler neck. All kinds of crap came out of the radiator drain. Since your radiator is fed from the top, it may not work as well. You may need to pull the radiator flip it upside down, and force water from the bottom radiator hose. You do not want to try to force particles down the entire length of the fins. Do this over a surface that you can see what comes out. It would probably not hurt to pull the thermostat, and force water through the head, block, and then out the water pump while you are at it.
It seems like a lot of work, but it beats the hell out of pulling the head, only to discover that the problem still persists.
#18
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I'm thinking it's a very good chance that the temp sensor ground is going ape ****. After I did my reroute, my needle was going up and down and all over the place...very quickly. Turns out that the spacer used and the new gaskates were isolating the sensor from being grounded. Try taking a piece of wire and attaching it to whatever the sensors are screwed into and grounding them to the engine. I know you've mentioned it was there for awhile, but I'd still try grounding to either find or eliminate an issue.
#19
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I have the same reroute.
it is very difficult to get burping right. 2 ways of doing it right.
1. use a vacuum pump
2. lift the rear of the car up, run the engine, wait till you see a big bubble (radiator will go empty). add water. then you do the same with rear lowered, front raised.
it takes many many tries to do #2, I ended up with #1, 15 minutes and done.
op: do you have a heater ? if not, did you put in a restrictor ? did you drill a hole on the thermostat and oriented at 12
see here for other recommendations on reroute:
M Tuned Coolant ReRoute - MX-5 Miata Forum
it is very difficult to get burping right. 2 ways of doing it right.
1. use a vacuum pump
2. lift the rear of the car up, run the engine, wait till you see a big bubble (radiator will go empty). add water. then you do the same with rear lowered, front raised.
it takes many many tries to do #2, I ended up with #1, 15 minutes and done.
op: do you have a heater ? if not, did you put in a restrictor ? did you drill a hole on the thermostat and oriented at 12
see here for other recommendations on reroute:
M Tuned Coolant ReRoute - MX-5 Miata Forum
Last edited by bellwilliam; 03-30-2010 at 04:01 PM.
#20
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It does not matter if the radiator is new, the scale would be coming from the block. It will take more than one flush to get all that scale out of the block. I must have flushed my car ten times, and it still had some rusty water. For a long time I did not have any antifreeze in the car, and after a while, it caused me some headaches.
Cleaned them all, more than once.
I'm thinking it's a very good chance that the temp sensor ground is going ape ****. After I did my reroute, my needle was going up and down and all over the place...very quickly. Turns out that the spacer used and the new gaskates were isolating the sensor from being grounded. Try taking a piece of wire and attaching it to whatever the sensors are screwed into and grounding them to the engine. I know you've mentioned it was there for awhile, but I'd still try grounding to either find or eliminate an issue.