Note: Yesterday I created this same thread but for some reason it never got posted. So I'm trying again. If the other thread is awaiting mod approval or something it can be deleted thanks!

So as the title suggests I'm a new owner of an 8! I posted a couple weeks ago about possibly buying one and I decided to dive in. To get a few things out of the way, yes I've been reading through lots of the old topics here and they have provided me with tons of information. I haven't read or found them all yet so forgive me if I ask or say something that appears to be blatantly obvious. Secondly I do not have compression test numbers yet, I have a test scheduled with a local dealership next week. I know I broke the golden rule of buying an 8 by purchasing before having the test done. reasons that I decided to do this are 1) this is not my primary car so its not really an issue if I have to let it sit for long periods of time (2) the overall "appeared" condition of the car paired with the price I paid for it was an acceptable risk for me if the engine turns out to be a dud, and (3) the general availability of these cars in my area is pretty low. I am also approaching this car as something I'm going to work on by myself and focus on restoring back to original as much as I can. I'm not a master mechanic so I obviously won't attempt engine rebuilds on my own, but I'm willing to learn as much as I can and do as much as I can within my ability to do.

Now on to the good stuff! The car is a 2004 MT RX8 Touring. The odometer has a little over 100k on it. As far as I know it is the original engine. As far as actual driving and running of the car, everything seems good to my untrained RX8 driver senses. The car starts up fine whether its a cold or hot start. It has lots of power in the higher parts of the rev range (>5k) the whole way to redline. Temperature gauge climbs up to about dead center and stays there. In general just lots of fun to drive.

The first of my questions comes from some readings that I am getting in the Torque app that I've hooked up to a bluetooth OBD2 adapter. Torque reports the following sensor "Catalyst Temperature (Bank 1,Sensor 1)" as having a "temperature" of ~450C immediately after starting the car. After letting the car idle for a few minutes the reading jumps up to ~750C. Are these readings correct or is Torque simply getting the sensor data wrong? The numbers just seem to be too high to be accurate. I do not know the state of the catalytic converter. I've done the "visual" check but after taking the car for a ~20 minute spirited drive the catalytic converter looks fine.

 

Those temperatures sound fine to me. My EGT runs as high as 1750F with a known good cat when the car is running hard. It averages about 1700F on the track and about 200F lower on the street. Rotary engines are well-known for producing high EGTs. Here is a graph from one 20 minute session on the track.



You will still want to make sure your cat is good, because if it isn't, it will kill your engine.

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Oh that's good to know then. Like I mentioned I'm still trying to get up to speed on everything and those numbers just seemed out of place.

There is a lot of general maintenance stuff I'm planning to do. By the looks of things a new set of plugs, coils, and wires is in order so i plan to tackle those after the compression test. Torque is also registering engine coolant at around 84C and engine temperature at around 220C after a ~20 minute drive. I've also noticed that the cooling fan will remain on after shutting the car off. I know this is normal and intended sometimes but it seems like its doing it all the time, at least after a normal driving session anyways. Should I be considering a radiator and coolant flush? or is this normal?

 

A coolant temperature of 84C is fine. What PID are you using to describe "engine temperature" of 220C?

The fans staying on is normal in hot weather if when you have been driving slowly for several miles or have been stuck in traffic.

The fans can weaken and decrease in speed with age. Yours could be weak, and that could be causing them to run more after turning the key off, because they are not providing enough cooling when driving slowly, stuck in traffic, etc.

 

Well where I live its barely Spring and the ambient outside temps are still in the mid to low 50's F. I haven't been driving it too slowly, with most of the speed limits for the roads I'm on are either 45-55MPH. So like you said maybe its just a weak fan.

I may have mis-spoke there I believe it was Engine Oil Temp. I'm not able to check it right now but how can I identify the PID in Torque? Sorry for being a bit dense. The bluetooth adapter is all I have for connecting to the OBD2 port. I can use another app if there is something better than Torque.

I'll look at it again this evening.

Thanks for the feedback.

 

So I apologize. I'm not sure where I was thinking I got that "engine temp" reading. Looking through the available sensors in Torque I don't have anything that would give me that number so I must have gotten some numbers mixed up.

Another thing to note, I took the car for a short ride to a gas station and back (~6-7 miles round trip) average speed of ~35mph. The cooling fan continued to run for around 3 minutes after turning the car off. Would flushing the radiator be a good thing to plan on doing soon? I don't know if it has ever been done.

 

My car wouldn't even fully warm up in the 3.5 miles it took you to get to the gas station. However, a 3 minute runtime after shutdown doesn't seem like a big deal, although it is probably not normal behavior. Flushing the coolant is certainly not a bad idea--especially at your car's age, but I don't think old coolant is actually the problem.

The best thing you can do is use Torque to log temperature data and give us as much information about the conditions of the drive as possible to help us interperate the logs. You will find that people around here are more than willing to help but we need as much information as possible to figure out what is going on with any given car.

 

If you flush your system, jic you don't know, it requires FL-22 compliant coolant.

 

Yeah thanks Cajun, I saw that from the DIY posts about using FL-22.

Thanks for the suggestion on logging Dallas. I'll post some data most likely on Monday since I plan on using it for work that day. That should provide measurements of a what a typical day's driving would be.

 

So I'm bumping this back since I finally had some time to do a few things with the car and now I'm looking for some opinions on where to go next.

First off I had the compression test done and everything came back with acceptable numbers (took me awhile to get the conversions down, thanks foxed.ca!). However the tech did say my spark plugs were in desperate need of changing. I had assumed they were bad and I have a new set of plugs, coils, and wires coming this week.

The issue I am having is cooling. The engine coolant temperatures seem to be on the high side. My average coolant temp hovers between 100C-108C. The gauge in the dash is obviously junk so the numbers I'm referencing are from Torque. I have two spreadsheets with log data from torque that track coolant temp, ambient air temp, RPMs and my GPS speed. I'm willing to post them if it would help diagnosing the issue.

The gauge in the dash never moves from center during normal driving, but if I where to do some full throttle acceleration causing the engine to stay in the +6k of the rev range I can get the gauge to move off center. The ECU will report temps of around 115C when this happens. Once I lay off the throttle the gauge goes back to center and the temp from the ECU will be around 104-106C

I have already done a coolant flush and refilled with FL-22 55/45. This didn't seem to have much effect. The coolant that was drained didn't appear to be severely dirty.

My question is where do I go from here? Thanks in advance!

 

See. I told you it isn't the coolant. :P

I agree that those temps are high. Some would say dangerously high.

Our cooling system is not really any different than any other modern cooling system, so the same troubleshooting steps apply. Some possibilities include obstructed radiator, dirty radiator, obstructed coolant hose, obstructed coolant passages, faulty thermostat, faulty water pump, cavitation, insufficient fan speed, insufficient pressure, air in the system, etc.

For reference, here is a chart showing how my OEM cooling system behaved on my Series 2 car on the track in hot June conditions. My coolant temp maxed out at 216F under heavy load and averaged around 212F (ignoring time spent in grid and warm-up and cool-down laps). Yours should not look worse than this when the car is moving faster than 50mph in the appropriate gear.



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Steve what are you using to create those graphs? Here are two charts i created from the log data I have from the two drives I did today. Chart 1 is my morning commute to work and chart 2 is the afternoon commute back. I apologize that they are so poor quality, google sheets has a long way to go before it can compare to Excel in that regard...

 

I recorded the data with either Torque or Harry's LT. I have a high resolution GPS that provides data at a rate of 10K, so other data looks blocky. The graphs were made with Excel.

What we really need to know is speed plotted against temperature, since you are posting daily driving data.

The morning chart looks perfectly fine, but I assume temps are chilly in PA in the morning (as confirmed by the IAT data), so that is to be expected. The afternoon data is hard to read without knowing the ambient temp and how fast you were driving. Judging by the IATs, it looks like you were in traffic. The coolant temps look to be nice and consistent, but consistently too high. I'm suspecting fans based on that chart, but also thermostat based on what you have previously posted.

 

I've attached 3 different CSV files with the data from the charts. They have Device Time, GPS Speed (converted to MPH), Engine Coolant Temp, IAT, and RPMs. The RPM readings don't seem to be completely accurate all the time. I suspect my bluetooth OBD2 adapter just can't keep up. I've attached 3 files because my drive home today was on a different set of roads (the distance was about the same and the actual speeds and traffic patterns were very similar) than what I drove in on during the morning commute. I included data from a commute home on the same roads as the morning commute from the day before. Just so we can be comparing apples to apples.

If there is anything else I should be logging let me know and I'd be happy to make adjustments.

Is there an easy way of telling if the thermostat is possibly bad? I'm suspecting not, other than taking it off and looking.

 

Welcome to the club man!

In your first few posts, you mentioned hour coolant temp was around 80 something. When you said the fans would stay on after shutdown, I knew it was way more than that.

The fans stay on for a 5 seconds after shutdown when the coolant temp is over 101C (213.8F). They'll stay on for longer only when the coolant temp is over 110C (or 230F), so your car goes over 110C when you turn it off. That is bad.

So we know it gets into the 110C range when you're stuck in traffic. If you're overheating ONLY at idle, it's definitely the fans, or the sealing around the radiator has been blown off. If you're overheating at speed too, then it could be a radiator/water pump issue. Here's a simple test to rule it out. How hot does it get when you're doing 60mph in 6th gear. I'm talking high speed, low rpm. To keep the engine as cool as possible. Drive at 60mph for about 2-3 minutes. Let us know the starting temp when you got to 60mph, and the final temp when you slowed down after 3 mins. Post the ambient temp too. Try it

Another thing you can do is seal around the radiator. It really works man. Trust me. You need to stuff foam around the radiator, so air doesn't leak around it. That's the top, bottom and sides. This stops hot air from the engine compartment from leaking around the edges of the radiator and coming back to the front, and getting sucked in again through the radiator. When 100C air gets sucked in through the radiator, your cooling capacity is greatly reduced. It also helps when you're traveling at speed. With the foam in place, air is forced to go THROUGH the radiator, and not around it. You want as much air to go through the radiator.

Good luck and keep us posted!

 

Ok I see that you've done what I told you to do in those log charts.

In the first chart, when the ambient temp is low, your car is fine. The second and third charts, when it's 30C outside, you're overheating.

Are you losing coolant? Have you checked for any leaks? Pressure test the cooling system.

 

I'd need to plot your data to get a picture of what's going on, but two things I noticed: Your fans don't seem to be bringing your coolant temperature down when you are stopped, and you are running hotter than you should at highway speed. Are you climbing a lot of hills?

Make sure you have properly de-aired the cooling system after your coolant flush.

You really don't ever want to see that dummy gauge move. I suggest you turn off A/C and decrease engine load when you see anything above 225 F.

 

Good point! Turn off the AC. It should help drop your coolant temps. You can turn on the heater if you wanna drop the temps even faster. The car's heater heats up the air using the cars coolant. So your coolant gets cooler lol.

 

A/C is not running in any of the data that I've posted. I understand that running the heater would cool the coolant down faster but I'm not going to be doing that in the summer months which is when I plan on using this car.

Jastreb, I de-aired the lines by having the front of the car elevated, leaving the coolant tank cap off and idling the engine for 10-20 minutes at least. I was also running the heater at full blast while doing this. Engine was definitely up to temp and I noticed gurgling or air coming out of the coolant tank. Not saying there still couldn't be air in the lines but I tried my best to get it out. I have not pressure tested the cooling system but I'm not sure how I could go about doing this.

I live in western PA so there are several hills I am climbing. They aren't necessarily huge or steep but its definitely elevation changes requiring more throttle. If I take it easy while driving and minimize sustained high RPMs, the coolant temp seems to stay within acceptable ranges (less than 103C). Thats provided I'm traveling at speeds greater than 45MPH. While driving in town the temp can rise to as much as 106-107C but will never really go over that.

I have data from my commute this morning which I never saw the temp go over 97C. The difference was the ambient temp this morning was only are 35F-45F. So rather cool. I'll post that data later as I can't do it at the moment.

 

I charted your speed vs. coolant temp. What we should see is some inverse relationship between the two. As your speed stabilizes above about 50mph, your temperature should decrease until you hit a stable cruising temp, which is governed by your thermostat. (This is not perfect, since revving the engine to increase speed also increases temp). That cruising temp should be somewhere around 180F. Mine is 179.6F. From there, it should increase and decrease with speed and RPM according to your inputs. Mine bounces around between 180 and 190F, but settles back down to 179.6F when I settle into cruising again. My temps never go above 200F when carrying any amount of speed except at the track, when I am pushing the car as hard as I possibly can. Your highway chart does not conform to what I consider to be normal behavior.

You can be driving at 60 to 70mph in a reasonable gear, and your car does not cool down below 220F. So, you are ostensibly putting a lot of air through your radiator, and it is ineffective at cooling your engine. What your fans are doing is immaterial at this point, because moving air across your radiator is not working. Your cooling system has some other efficiency problem.



mobius1's cooling efficiency at highway speeds




mobius1's cooling efficiency in traffic




My guess is your thermostat is not opening completely. Thermostats are so inexpensive, they really aren't worth testing. If you really want to go crazy, you can buy a lower temperature thermostat that will start opening about 10F cooler and hold off heat soak longer.

I just noticed your car has 100K miles on it. A lot of people like to replace the water pump and thermostat as part of 100K maintenance. Also think about how much junk flies into a radiator that sits as low to the ground as ours. Your radiator and condenser are bound to have a lot of gunk stuck in them. A good cleaning would probably help. Also clean your oil coolers while you are down there.

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Steve I'm thinking you are correct, and it makes more sense the more I think about it. I'll take a look through the DIY threads on changing the thermostat/water pump. I've not done a water pump/thermostat change before so I'll have to see if its something I can handle on my own.

I'm guessing there is no real preference on which thermostat/water pump to go with? I know I've seen the one on Mazmart mentioned numerous times. Any others to consider? Far as I've been able to find so far an OEM thermostat runs for about $40-$50.

 

Quality thermostats can be had for as little as $10. Changing the thermostat is pretty easy with minimal loss of coolant. Do that first and check your results. (And clean your radiator and condensor!) The water pump is not terribly difficult, but you will need to drain the coolant from the radiator and engine block. Water pump failure usually involves coolant leakage. If you aren't leaking coolant, your water pump is doing its job for now. The question is, how long will it continue to do so?

 

I was definitely going to do the thermostat first before the water pump. I know it didn't really sound like that, I was just planning for a worse case scenario. I'll be cleaning out the radiator/condenser as well. This sounds like a nice weekend project, if I can find a local shop with a thermostat in stock.

On a completely different topic I noticed that you have a BHR Midpipe and an aftermarket cat does that combo keep you from getting CELs? I saw that BHR sells their Midpipe with a "catalyst" option but I haven't looked into what that means exactly. I unfortunately live in an area that has "visual" emissions testing. I have my heart set on a nice midpipe but I'm not sure which to get yet and I haven't researched how to get around the emissions testing.

 

The earliest water pumps had problems with creating cavitation. That was fixed at some point, but I'm not sure when. The information is on this forum somewhere. The Mazmart Remedy water pump supposedly fixed it early. They also have thermostats at OEM and lower temperatures. Mazmart is a top flight company, so you will be in good hands should you decide to deal with them.

The only midpipe worth having is the BHR, IMHO. The rest of them will fail or make your ears bleed. BHR's catalyst option should perform just fine on a street driven car. I track my car up to 15 times per year, so I need something very robust. I am trying an HJS motorsports cat. It works fine for now (no CEL and little stench), but I can tell the catalyst is suffering after only 1 1/2 track days. Hopefully it will hold up.

Whether to go with a cat or not is a personal decision. On one hand, rotary engines and cats are largely incompatible. The engine eventually clogs the cat, which then kills the rear rotor in the engine. Going catless solves that problem, gives you back a few HP, and saves you a few pounds of weight. On the other hand, the stench produced by rotaries is legendary. It permeates your hair and clothes. You wear it like cheap cologne. If you start the car in the garage, it permeates your house too. I went catless for 2 years, but recently had one welded in. I just couldn't stand it any longer, and no one would ride in my car more than once. It was nostalgic at first, since I grew up before cats were prevalent, but it got old quickly. Even my track friends were unimpressed with the smell.

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So I'm bumping this thread hopefully for the last time. I just wanted to give a big shout out and thanks to Steve here for helping me troubleshoot through my temperature issues. Along with everyone else that gave suggestions.

Long story short, I replaced the thermostat, cleaned my radiator and everything is running solid now. I'm maintaining coolant temperatures between 82C-88C which should be bang on the money. I've even replaced my plugs, wires, and coils while I was at it. So all in all things are running smooth.

My only hiccup in this whole process is I've seemed to have developed a low coolant light that will come on briefly and then go out again. I have been monitoring my temps with torque and everything is fine when this happens. I'm assuming its a failing sensor in the coolant tank but I thought I'd throw it out here in case anybody has suggestions on something I could do about it or check. I know the coolant levels are fine and there is nothing leaking from the car.