Fahim Amjad

My rx8 slightly only overheats when i drive it hard,suppose if i redline it in every gear on highway for 6-7kms,then the heat needle slightly goes past the middle or centre point,and if i slow down,within 2-3 seconds the needle gets to normal/middle of the temp gauge.
ambient temp was 31c outside at night.

Loki

iTrader: (1)

Do you have the plastic engine undertray, especially the part under the radiator? Really need that for effective cooling at speed.

Fahim Amjad

Any pic?
i bought rx8 used,dnt know how the tray looks.

Fahim Amjad

previous owner used to run the car with water only,and i saw the water was rusty,so i changed the water with fl22 coolant,drained all the water,and poured 8L coolant inside radiator and block.

Loki

iTrader: (1)

Can you see the ground through the radiator opening in the front bumper? If so, you're missing the undertray and air is going under the car instead of through the radiator.

It looks like that:

Fahim Amjad

i have this thing!

Fahim Amjad

so what can be the problem?
need help.

UnknownJinX

If there is rust in the cooling system, might be a good idea to flush the system a few times. There could be a clog somewhere.

I have even see cases where water pump impeller is rusted away, but I am not gonna jump to conclusions yet.

Fahim Amjad

this were the condition of pipe,and pipe connector,
pipe connector is changed,and pipe is cleaned before adding coolant.

Loki

iTrader: (1)

There might be chunks of that pipe blocking parts of the radiator. This isn't going to be fun, unfortunately.
Unknown is right, I would take the water pump off and see what condition it's in. Using undistilled water allows electricity to conduct through the coolant and erode dissimilar metals the same way a battery does. Brass, aluminium, iron, etc.

Actually, before you do anything else, either have a compression test done, or check your coolant for exhaust gases (its a chemical test that any mechanic can do). All this corrosion could have damaged the water seals in the engine, which is why things get hot when you run it hard.

Fahim Amjad

Slight overheat,and comes to normal within couple of seconds if i stop redlining. Compression tested few months ago,was 105psi in three cylinders,and 100psi in other cylinder.

Loki

iTrader: (1)

This car doesn't have cylinders, it has 2 rotors. There should be either 2 compression numbers, or 6 (if it was done with a proper rotary comp tester). RPM is also important

Another thing to check is the internal condition of the catalytic converter. Just in case.

UnknownJinX

At this point, it's good to read up on these cars using the links in my signature.

As Loki said, these compression numbers are pointless without 3 of them on each rotor, cranking RPM and elevation. It should be something you did before purchasing the car(unless you spending under a grand for the car), but yeah, worthwhile to check it out and see what you are up against.

The fact that someone would use water(and undistilled water at that) as the coolant is very concerning.

Fahim Amjad

Here’s the test report.

Fahim Amjad

btw this a 2004 model car,with AT transmission,still now using the cat tht came with the car from factory.

Loki

iTrader: (1)

Oh nice, you had a real compression check. Not everyone does, unfortunately. The results aren't amazing, but you have time to make a plan.

I think the recommendations still stand:
- examine water pump
- examine inside catalytic converter
- I'd still do an exhaust gas test on the coolant
- something else you could do is as a quick test is start the car COLD, remove the coolant cap, and let it come up to temperature. See if the coolant in the overflow bottle bubbles. It should not.

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Fahim Amjad

as i mentioned before,car slightly overheats if i redline it continuously for 30-40mins at 30-35c ambient temp.
and comes to normal temp within 3-4sec if i slow down to 40-50kph.
so i think if its waterpump,then it would have overheated more easily.

Loki

iTrader: (1)

True. I didn't catch that it took 30-40 minutes to get to that point. For comparison, I think I got the needle to move once on a hot (30+) track day after 20-30 minutes on a relatively slow 2nd-3rd gear track. I'd still check everything out since the previous owner clearly didn't follow proper maintenance, but if you want to do what you're doing and not overheat, you can upgrade the radiator. I'm not sure what options there are for an auto, but there is a CSF model that's a great upgrade for manual RX8s. The rads are different.

Fahim Amjad

so is it normal for a rx8 to get slight hotter than normal with such driving and ambient temp?

Loki

iTrader: (1)

"Normal", sure everything has limits. Desirable? absolutely not.

Fahim Amjad

then what should i do now?
can a thermostat which only opens half when car reaches operating temp,cause this thing to happen?

Loki

iTrader: (1)

If your thermostat isn't fully opening you would probably overheat a lot more. You have several suggestions above on what to do next. Combination of making sure the cooling system components are working as expected and upgrading to support your needs. I wouldn't take too many trips past the half way mark on the temp gauge.

Fahim Amjad

bt brother,as u said to test for gas in cooling system,which means u r doubting the water seals,if the water is problem,then water level in reservoir tank would have getting lower more often.
after removing all the water from cooling system and pouring coolant in it,i have driven 60-70km without any coolant loss.