Diinj27

The silver beast
HI all,
I have a 2005 RX8 6 port .I have the car for almost a year now. Car been driving fine engine temp 88C - 96C normal driving and under heavy load 103C Max. This week it overheat suddenly engine temp rise twice in seconds from 91C to 110C(100m distance) while cruising to my house. One time rise to 110C and back to 91C very quickly. All engine where monitor via OBD2 scanner. Some coolant spray from overflow tube.


Mileage 129000km ( 80200 miles)
Engine mineral oil 15w40 motul
new coils, plugs, plug wires, New coolant 6 months ago. New air filter oem, oil filter.
cold and hot start good
no exhaust smoke

from what I've read already on the forum for overheating could;
1- trap air in coolant system
(Ive bleed the system letting it idle with cap off)
2-bad water pump
( checked no leaking through weep hole)
3-Stuck close thermostat
( just been replaced 3 months back)
4-crack coolant hose
( no coolant dripping or pubble under the car )
5-engine coolant seal
( no white smoke form exhaust on start up or while driving)
6- or block radiator

Any advise please ?

dannobre

iTrader: (3)

Are the fans working correctly? Check coolant temp.sensor readings if you can to see if they make sense

Thermostat? Even if it's a new.one they can fail...

Water pump? Although it's not usually on and off again working. And they usually leak when they die

check the coolant overflow for lots of small bubbles... that could indicate a seal breach... although it will usually puke coolant.

Diinj27

With OBD2 monitoring - Fan low speed at 96C and fast speed at 102C. That said at low fan speed can hear slight noise. Is that normal ?

When temp rises I usually hold rev to 2000rpm to lower by 2-4 degrees. Is that also an indication I need a new water pump?

Some bubbles in coolant overflow but no white smoke.

dannobre

iTrader: (3)

The fans will be quite loud... especially on high

CaymanRotary

Could be a combination of the fans or a problem with the radiator. Definitely have a problem. Is it a stock system? I always upgrade the cooling system on these cars because Mazda did such a **** job making the one that came with the car. Radiator is complete trash.

wannawankel

IIRC I remember a "burping" procedure for the coolant system when there's a total coolant change (drain from radiator and block) and refill. My S2 manual says:
Refill the engine coolant into the coolant reserve tank up to the F mark.
8. Install the cooling system cap.
CAUTION:
If the water temperature gauge rises too high, stop the engine and decrease
the engine coolant temperature to prevent overheating. Then, verify the
malfunctioning part and repair or replace it.
9. Start the engine and warm up the engine by idling.
10. After the engine warms up, perform the following steps. At this time, be careful of the
engine coolant temperature to prevent overheating.
a. Run the engine at approx. 2,500 rpm for 5 min.
b. Run the engine at approx. 3,000 rpm for5 s, then return to idling.
c. Repeat step (2) several times.
11. Stop the engine, and inspect the engine coolant level after the engine coolant temperature
decreases. If it is low, repeat steps 7—10.
12. Inspect for engine coolant leakage

wannawankel

What do you upgrade in terms of cooling system?

Diinj27

On low speed sound like a worn bearing.

All stock system. Both fan work at temp. I feel they not as fast as it should be. Do fan slow down with time? For the radiator won't it overheat while driving as well if its clogged or only at idle ?

Thanks , I'll try this procedure and see 🤞
cooling system stock

Diinj27

update so far.
1- I've change the cooling fan with a new oem unit, as the previous one was making a bearing noise and I think it was running slower than it should
2- flushed clean the radiator and now running 90% water
3- Brace the undertray properly as it was sagging down and letting air escape under the car rather than directing it to the radiator

Results so far
Coolant temp 81C -91C instead of 98C-102C around town.
Under heavy acceleration up to 120 mph 93C max

CaymanRotary

Good stuff!! Always have an issue with the stock cooling system. Always second upgrade on any new 8 I add to my collection. First being the ignition system. Keep those two things happy and you'll never have a problem.

jcbrx8

Good recommendations, but "...never have a problem"? I'll take "...minimize problems."

CaymanRotary

As far as the engine goes, shouldnt have an issue anyways. Of course, nothing lasts forever but the engine will last a lot longer.

UnknownJinX

90% water? What's the other 10%?

Diinj27

90% water /10% coolant.
Running great now.