Peaul

Hey guys, I posted a while ago about getting my aunt's 08' RX8, and I got it to run great until a couple days ago. I have a couple of questions about my car overheating.

The Symptoms:
My car only overheats when I'm stopped in traffic, and the temp gauge gets to 3/4ths of the way up, sometimes a little higher. When I'm driving, it doesn't heat up at all, and if it's already heated up it cools down a little. When I stop, no coolant appears to be leaking out of the bottom of the car, however sometimes the coolant starts to boil a little bit. The oil dipstick was not milky at all when I checked that, so I don't think any coolant was leaking into the oil.

What could be wrong with my cooling system? I know I'm probably losing pressure somewhere since the coolant starts to boil, but sometimes everything is fine and the car doesn't overheat at all. Could I have a faulty coolant cap? I'm trying to stay as cheap as possible but if something is seriously wrong I'll shell out the money to fix it, since this is my daily commute car. Is it even safe to drive it when the gauge is 3/4ths of the way up? This has only happened two or three times, and I always try to stop as soon as possible, so hopefully I'm not doing any serious damage.

Another note, my roommate drove my car 2 nights ago(don't worry I trust him) and he said the gauge didn't go up at all, even when idling for long periods of time. I just think it's weird that sometimes it runs fine, and sometimes it starts to get hot. Everything else is fine(oil, plugs, coils, etc.), it's just the heating I'm having troubles with. If anyone could help me that would be fantastic. Thanks! (BTW I've read the beginner thread and searched this website for answers, and I haven't found anything similar to my problem)

200.mph

iTrader: (9)

if the temp needle moves past the halfway point you are in serious trouble. its not an actual temp gauge, its a dummy gauge. are you low on coolant? i would suggest a leak down and pressure tests right away and not drive it until you have figured this out. overheating a rotary is very very bad. you could have easily blown a coolant seal already which requires a rebuilt to fix

Peaul

Alright, I knew I would probably have to get it pressure tested. I assume I can take it to a regular mechanic to do this? I live in a super crowded apartment and there are no rotary specialists anywhere near me. Also, would you happen to know how much a pressure test would cost?

200.mph

iTrader: (9)

probably about an hour worth of shop time ~$65. get a leak down test too. its a chemical test to see if you have combustion gases in your coolant. where are you located?

Peaul

I'm in College Station, Texas. Unfortunately I know nothing about the mechanics here, so I'll have to do some research.

UnknownJinX

I would advise against driving your car until you sort this out. You are lucky that you haven't warped the housings yet.

You might be able to borrow a cooling system pressure tester for free at an auto store. Some of these tools can also check the cap.

Loki

iTrader: (1)

Are the fans turning on? That would be one of the few things that would cause an overheat while stopped but not while moving.

If they're not, check the fuses, then the fans themselves for obstruction.

dannobre

iTrader: (3)

Fans....

Peaul

I'll have to double check, but I'm pretty sure the fans were turning on. If they are turning on, and my system is holding pressure with the tester, would the problem lie in the cap?

Loki

iTrader: (1)

The cap is cheap enough to replace just in case, but if you think about it, the cap and most of the cooling system acts the same whether you're stopped or moving. If you're only overheating while stationary, that's a sign that not enough air is going through your rad, or that not enough water is being moved around. The first is fans (check that both of them turn, at high speed). The second is water pump, but that would be an extremely unusual failure.

jakejm79

I see it being one of 2 things:
1. Lack of air flow through the radiator, either an Issue with the fan(s), either they aren't being triggered at the right temp or they aren't moving enough air (spinning too slow or broken deformed blades) or the radiator itself (blocked/dirty fins, etc) at higher speeds there is extra air volume that helps to off set this.
2. Inefficient coolant circulation, either due to a partial blockage or WP issue, maybe at the higher RPM of driving the WP is moving fast enough to mask the issue.

Have you tried running the heater when it starts to overheat, if that doesn't make a difference it could point more to #2 rather than #1, tho it isn't a definitive test.

Also just to correct some terminology in a previous post, a "leak down" test isn't what you want, that is a test for checking compression and obtaining where the lack of it is coming from and is generally reserved for traditional cylinder engines, its not really even feasible to do a leak down test on a rotary engine. You will want to ask for a combustion gas leak test aka coolant exhaust gas test.

04Green

iTrader: (1)

Fans - turn AC on, do fans come on?

Foam - need to make sure hot air does NOT get back around radiator from engine compartment. The Congrats Thread in my sig will tell you what to do.

Also, Check out https://www.rx8club.com/series-i-tro...o-i-do-258334/ for troubleshooting tips.

Peaul

Update:

Lots and lots of coolant come out of the overflow pipe when it gets hot(I'm pretty sure it was never this bad though). Obviously I have a pretty bad leak somewhere. However, my exhaust doesn't smell, there is no coolant on my oil dipstick, and I'm noticing zero performance issues when I revved it up, so I'm led to believe that there is no coolant leaking into the engine. Fans come on when they're supposed to, and I think they are running at full RPMs. Is my course of action to rent a pressure tester and try to locate the leak? I'm going to change my oil and double check that there is no coolant there.

200.mph

iTrader: (9)

might as well save your money for a new engine since you dont listen to us and keep driving your car without fixing the very serious overheating issue

Peaul

I wasn't driving it :/ I let it heat up for 5 minutes in my parking garage, said symptoms happened, shut it off immediately when the temp gauge moved off middle.

UnknownJinX

Renting the tool is free, so why not.

200.mph

iTrader: (9)

sounds like its not circulating. water pump, t stat or a blockage somewhere.

Loki

iTrader: (1)

Don't worry about the oil, if it's not milky, it's fine. There is no head gasket
If it came out of the overflow tube, sounds like the cap is not holding pressure. Perhaps try that first?

But yeah, none of this is a great sign. Get that pressure test done too.

Silly question, is the water pump belt on and intact?

200.mph

iTrader: (9)

no but there are coolant seals that can fail just like a head gasket which is why i also suggested a leak down test.

op if you remove the cap and start the car are there small bubbles in the coolant? you will probably need a flashlight to see in there

Peaul

I will check the water pump and coolant bubbles in 30 minutes. Thank you guys so much for the help, I really appreciate it.

Peaul

Alright, update #2:

No bubbles in the coolant, and it was swirling pretty good. Water pump belt seems to be on and functioning.

I'm going to get that pressure test done on Sunday. The radiator was pretty dirty down under so I'll be cleaning that out as well. I'll probably flush the coolant out, as I have no idea how old that coolant is anyways. If none of that works, I'll change the thermostat and pressure cap, if that doesn't work, I guess I'll start looking into a new radiator? Probably need a new one anyways.

NotAPreppie

If it's boiling out of the overflow tube then one of two things is happening:

1. Your cap isn't sealing properly. The cap has two seals which create a space between them. The overflow port sits in that space. The lower seal (on the spring-loaded section) is that cause in this failure mode. Take a clean, lint-free, damp cloth and wipe both mating surfaces thoroughly. It may just be a bit of dirt preventing a good seal. Most pressure testers will include an attachment to test the cap as well.
2. Coolant isn't flowing well enough and is boiling in localized hot spots. This would exceed the pressure rating of the cap and you'd get coolant puking out of it. Since you see coolant moving through the air separator tank, it's likely that the water pump is good. The problem could be a bad thermostat, radiator clogged with schmoo, pinched/collapsed hose, or something else. If you turn your HVAC temperature **** to the hottest setting and get hot air from the vents then I doubt it's the thermostat.