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Mysterious high temperature issue... Overheating? Or bad sensor?
2007, Series 1, 6 speed.
Hello all,
First time writing so be gentle,
I've been a member for a while and have found many useful bits of info, ideas and fixes for my RX8 during this time, so a big thanks to all who contribute to this site ( even if some info is incorrect) we can all learn from each other. OK, that's enough butter.... I've been having some trouble diagnosing a 'overhaeting' issue. Temp guage moved while I was driving spirited, (felt my stomach sink a little) immediately slowed down and temp guage returned to normal position. Did some checks at home the next day:
No leaks, anywhere.
Coolant level full. No spray.
Thermostat changed to Mishimoto. Opens fully a few degrees cooler than OEM.
Bled cooling system properly. (No air bubbles) Even removed coolant hose from throttle body while nose was elevated to make sure.
Started up, checked for leaks. None.
Checked hoses for stiffness: Squishy when cold, firm when hot, as it should be.
Both radiator fans are also working properly.
Topped up coolant.
Reved up for about 2-3 mins at 3K. Still no leaks.
Redline it a couple times. No change on temp guage. Both radiator fans on.
Shutdown engine, fans stay on for about 5-7 mins as they normally do.
I was feeling pretty good until I took a easy drive that evening and saw the temp guage move up again. Even driving chill.
Anyone have any insights into this? Maybe a similar problem?
I have extensively searched the forums, but haven't found anyone who has had a problem like this.
Thanks in advance, and I apologioze if this has been solved and I just couldn't find the thread.
How many miles on your radiator ? At 100k, anything original in the cooling system is really suspect and failure prone. It represents the biggest threat to your engine.
Last edited by gwilliams6; 05-26-2018 at 07:10 PM.
How many miles on your radiator ? At 100k, anything original in the cooling system is really suspect and failure prone. It represents the biggest threat to your engine.
The car has 84K on the odometer and I changed the radiator to a KoyoRad about one year ago after my OEM radiator sprung a leak.
And, are you sure BOTH fans are on? Just one can do more harm than good.
And, there are a few cooling things in the congrats thread that I suggest looking at.
Driving chill, lol. Nothing over 50MPH and nothing over 5K RPM. Yeah I'm sure both fans are engaging. I removed the airbox and the guard to see for myself during some tests. But with the engine bay put back together I rely on the noise it makes, it's noticeably louder when both are engaged.
Thanks for the link, I'll check it out.
There are some pads around the OEM radiator that make sure the air will be forced through the radiator, not around it.
When you replaced the OEM one, did you make sure the new Koyo has some kind of padding around it to make sure the air only flows through the radiator?
Interesting theory. No I did not add any padding around the radiator. I know some people use expanding foam and other like matrerials for that, but I have been running the Koyorad for a little over a year with no overtemp issues until now. Maybe it is worth a look, it never overheats while revving, only while under load (dirving). Seriously... I revved the pants off her and temp gauge didnt budge. Drove for ten minutes and the needle shifted up.
I'm going to have my mechanic come by asap and plug into the comp. to see if it's trying to tell me something.
Things to consider...
- jammed thermostat (even though you replaced it, there could be a foreign object obstructing it)
- compromised water seal such that exhaust gases enter the cooling circuit. Test coolant for exhaust gases (there's a simple chemical test, any parts store can help you)
- cooling circuit is unable to pressurize. Cracked overflow tank (a crack elsewhere would produce a leak you would notice) or failed rad cap
- actually bad sensor, but that's pretty rare. They're simple devices.
Things to consider...
- jammed thermostat (even though you replaced it, there could be a foreign object obstructing it)
- compromised water seal such that exhaust gases enter the cooling circuit. Test coolant for exhaust gases (there's a simple chemical test, any parts store can help you)
- cooling circuit is unable to pressurize. Cracked overflow tank (a crack elsewhere would produce a leak you would notice) or failed rad cap
- actually bad sensor, but that's pretty rare. They're simple devices.
What coolant are you using?
All great suggestions, thank you.
Jammed thermostat - Could be. I did a basic check while idling, on the stiffness of the hoses while cold and they were soft, then again when hot (fans on) and they were solid which would indicate the thermostat opening and allowing coolant flow. Right? I mean, I'm not a professional but that does make sense.
Compromised water seal - I will have to look into this.
Cooling circuit unable to pressurize - Rad cap did look a little worn so I replaced it 3 days ago. Cracked overflow tank, it's not impossible but I have no visible leaks anywhere nor am I losing coolant. It's at the same level its been at since the thermostat install.
Bad sensor - I was thinking about this recently, because this new thermostat does open a few degrees cooler that the OEM one maybe the ECU is a bit confused and isn't sure how to handle it?
I used a Prestone coolant and water mix. 50/50 (or thereabouts)
I know Prestone guarantees compatibility with all makes/models, but the general wisdom around here is to use Mazda FL22 only. Something about 2-EHA, which FL22 doesn't have, being corrosive to rotary coolant seals.
I have the same thermostat as you and nothing freaks out. There is nothing the computer can do to react to a low temperature anyway.
The soft/hard hose thing is a decent indicationthe system has pressure, but not whether the thermostat is fully open.
Does your car still have the plastic undertray under the engine and rad? You need that, it's an active part of directing air to the rad. People have overheated without it.
One simple test of the sensor would be another thermometer. An infrared one if you have it, but anything that goes to 100C will do. The block should be close to the reported water temp if the car is idling stationary.
Is the rebuild a Mazda one? There were issues with their process long ago where extra sealant would be left behind and work loose in the water stream, and eventually end up jamming something important. There hasn't been a case reported here in ages,. ut you never know. Anyone can make a mistake.
BTW, the needle moves around 230F. You're going to eant to minimize the time you spend near there, these engines don't survive that temperature well.
I know Prestone guarantees compatibility with all makes/models, but the general wisdom around here is to use Mazda FL22 only. Something about 2-EHA, which FL22 doesn't have, being corrosive to rotary coolant seals.
I have the same thermostat as you and nothing freaks out. There is nothing the computer can do to react to a low temperature anyway.
The soft/hard hose thing is a decent indicationthe system has pressure, but not whether the thermostat is fully open.
Does your car still have the plastic undertray under the engine and rad? You need that, it's an active part of directing air to the rad. People have overheated without it.
One simple test of the sensor would be another thermometer. An infrared one if you have it, but anything that goes to 100C will do. The block should be close to the reported water temp if the car is idling stationary.
Is the rebuild a Mazda one? There were issues with their process long ago where extra sealant would be left behind and work loose in the water stream, and eventually end up jamming something important. There hasn't been a case reported here in ages,. ut you never know. Anyone can make a mistake.
BTW, the needle moves around 230F. You're going to eant to minimize the time you spend near there, these engines don't survive that temperature well.
Loki,
Thank you for your reply. I will look for that coolant at my dealership. I live in Barbados and it's sometimes difficult to find speciality products like that.
I have not removed the plastic undertray.
The car is still on it's original engine.
I'll look into the thermometer reading idea, thats a good way to rule out certain theories.
I'm compiling all of these great ideas and hopefully have my mechanic come by soon so we can go through them and get to the bottom of this. I miss my braps
The foam may be a biggie. What you are missing is air flow through the radiator. I do NOT recommend expanding foam. What I use is pipe foam, for a 1" or 1.5" pipe. It is fairly rigid and can be wedged or taped in place to fill the large gaps. What happens if this is not done is the air just flows around the radiator. The fans cut off at 20 something mph, the shroud is in the way, the battery tray is in the way and heat shield for the air box is in the way. By far the easiest way for air to get by is around the radiator.
You can put the foam in from the bottom, with the undertray out.
Any easy way to check the temperature is to use a thermocouple or a infrared temperature meter. They are easy to find online or some stores. That way you can verify the sensor is working.
Have the coolant cap checked for pressure leaks. A loss in pressure in the coolant system will result in a dramatic lowering of the boiling point of the coolant. Unfortunately our system runs at high pressure to elevate the boiling point and any losses in pressure result in a boiling point depression.
The foam may be a biggie. What you are missing is air flow through the radiator. I do NOT recommend expanding foam. What I use is pipe foam, for a 1" or 1.5" pipe. It is fairly rigid and can be wedged or taped in place to fill the large gaps. What happens if this is not done is the air just flows around the radiator. The fans cut off at 20 something mph, the shroud is in the way, the battery tray is in the way and heat shield for the air box is in the way. By far the easiest way for air to get by is around the radiator.
You can put the foam in from the bottom, with the undertray out.
That sounds like a great diea (even if you're not having overheating issues) I'll definitely look into that as soon as I get a day off work.
Have the coolant cap checked for pressure leaks. A loss in pressure in the coolant system will result in a dramatic lowering of the boiling point of the coolant. Unfortunately our system runs at high pressure to elevate the boiling point and any losses in pressure result in a boiling point depression.
Very useful information. Thank you. I did have the system pressure checked Two days ago and the system was sound. I completely re did the thermostat install and cooling system flush last night just to make sure there weren't any missed steps by myself or any kind of blockage in the lines. I also used roughly 60/40 distilled water & water wetter instead of coolant & water. Got an OBDII scanner tool as well so I could monitor the temperature in real time. Pleased to say that after 30 mins of idling and about 5 mins at 3K RPM the temp did not go above 212F. Secondary fan came on @ 210F with no airflow into the radiator and intake air temp @ 90F. I did not get a chance to drive test last night, but I will shortly.
So after many, many tests. My mechanic and I have come to the conclusion that the water jacket seal must be compromised as there is no other explanation that supports the 'type' of overheating issue I am having. I have exhausted all other theories. I've learned a lot through this experience tho so at least I got something out of it. Good news is, I had planned on having my engine rebuilt & street ported in July anyway so I already have all the new parts including Atkins Rotary new water jacket seal which they claim to be able to handle upto 150 deg. over the stock seal, so thats a plus. Now, if after the rebuild, its still overheating then we can have more discussions lol.
Just wanted to say thanks to everyone who had any form of input in this thread as all information was useful in some way. Great community. Great cars.
So after many, many tests. My mechanic and I have come to the conclusion that the water jacket seal must be compromised as there is no other explanation that supports the 'type' of overheating issue I am having. I have exhausted all other theories. I've learned a lot through this experience tho so at least I got something out of it. Good news is, I had planned on having my engine rebuilt & street ported in July anyway so I already have all the new parts including Atkins Rotary new water jacket seal which they claim to be able to handle upto 150 deg. over the stock seal, so thats a plus. Now, if after the rebuild, its still overheating then we can have more discussions lol.
Just wanted to say thanks to everyone who had any form of input in this thread as all information was useful in some way. Great community. Great cars.
KR.
Douglas S.
Wait Have you tested the coolant for exhaust gases?
Here's the thing: if the problem is in the engine, you rebuild it, everyone is happy. If the problem is outside of the engine, you rebuild the engine only to come back here with the same problem. So before you pull the engine, try to conclusively prove the source of the problem.
If the pressure check does not show a problem, it is not seal related.. Read Loki Post above again. It would suck if an external problem hosed your new build.
Did you try the foam around the radiator? Also, is the undertray tight against the frame rail? If you are not losing water I have a hard time thinking you have a water leak. But, airflow could be a problem.
And, Ultra-gauge. It will let you know exactly what is happening, what situation makes the temp go up, and what makes it go down.
And, check the CAT. Just pull the bolts at the front and look inside.
If the pressure check does not show a problem, it is not seal related.. Read Loki Post above again. It would suck if an external problem hosed your new build.
Did you try the foam around the radiator? Also, is the undertray tight against the frame rail? If you are not losing water I have a hard time thinking you have a water leak. But, airflow could be a problem.
And, Ultra-gauge. It will let you know exactly what is happening, what situation makes the temp go up, and what makes it go down.
And, check the CAT. Just pull the bolts at the front and look inside.
Pressure guage did not show a problem when tested, however I have been driving a short distance to and from work for the past 3 days and the coolant level has reduced without any visible signs of leaking. During my drives I do not allow the temp to go above 220F and through out this entire issue I've been having, I have never let the engine reach a 'critical' overheating temp. I've always stopped and allowed to cool as soon as the guage moved or if moitoring on OBDII as soon as it gets to 230F.
I cannot find the chemical test here in my country unfortunately (most shops have never even heard of it) and there is too much red tape to ship here.
Yes I have placed pipe foam around the radiator to channel more air into it.
I definatley do not have and external coolant leak.
Gutting the CAT was one of the first mods I made to the car, about 3 years ago.
Having the engine under any load causes the heat to go up exponentially. She will idle and rev all day long without much change in temp, but as soon as you start shifting above 4/5K temps rocket up. Or driving casually up an incline. I've actually based my routes around the steep hills so that I don't have any issues lol.
Thermostat could still be an issue. Pressure goes both ways. If it is not working, entire system will be pressurized so hard and soft hoses does not help.
Also, if you put the heat on high, does the temp drop? This adds more cooling to the system. If it does, then you are likely short cooling capacity. Again, that points to thermostat. I would suggest pulling the thermostat and tossing it a pan on the stove to test. See when it opens (meat thermometer will do the trick). You could also try a test with the thermostat out. This is not a long term option, but would give you data. If it stays cool, thermostat. But, it can still run hot with thermostat out if flow is too high (water does not spend much of any time in the radiator).
...and the coolant level has reduced without any visible signs of leaking.
If your coolant level is continuously doing down, and you do not have external leaks, and you do not have white smoke in your exhaust, you are either boiling it or you still have air in the system that is slowly bleeding out. My money is on the latter. When I replaced my radiator a few years ago, I carried a jug of distilled water in the car for about a week and topped off the level every time I shut the car off. Even though I followed the burping procedure in my garage, I did not get all the air out of the system in one shot.
Thermostat could still be an issue. Pressure goes both ways. If it is not working, entire system will be pressurized so hard and soft hoses does not help.
Also, if you put the heat on high, does the temp drop?
No. Turning on the heat does not lower the temp.
I did do the thermostat check (not with a thermometer) just to make sure the mechanism was working. I even checked the old one I replaced and that one is working as well.
If your coolant level is continuously doing down, and you do not have external leaks, and you do not have white smoke in your exhaust, you are either boiling it or you still have air in the system that is slowly bleeding out. My money is on the latter. When I replaced my radiator a few years ago, I carried a jug of distilled water in the car for about a week and topped off the level every time I shut the car off. Even though I followed the burping procedure in my garage, I did not get all the air out of the system in one shot.
Yeah you might be onto something there.
I drove the car all day yesterday and my temperature didnt go above 220F because I was mostly in traffic and driving slowly. Short shifting under 3K. I did one hard pull on the homestraight to my house and temp went from 212F to 232F very quickly. I could smell that sweet coolant smell but still no leaks and no white smoke. Coolant level was slightly lower this morning.
05-26-2018, 06:15 PM
Mysterious high temperature issue... Overheating? Or bad sensor?
Have you tested the coolant for exhaust gases?