I'm having an issue when I bring the car past 70mph the coolant temp (oem) starts to creep towards 12. I usually let off the gas and stay at 65mph or less and it always drops back down to the normal position.

It does not happen when I drive it on roads or redlining, just when the mph exceed 70.

I have replaced the oem radiator around 20k ago due to the plasric cracking and had a coolant flush done during that time as well. However, this issue just started recently.

Always do an oil change every 3k.

 

I'd park the car till you get it fixed, you can blow a coolant seal before the needle moves at all, so when it's moving, you are in danger territory. It's not worth risking the engine.

You don't state the mileage, but I'm guessing you are getting up there. I'd start by flushing the coolant again, then pressure test the cooling system, then replacing the coolant bottle, cap, and thermostat, if no improvement, replace the radiator again, and replace the coolant lines too while you are at it. Mazmart has the best prices for OEM stuff, you can get it all for around $500-600.

 

I'm at 81,000.

Usually, only happens when it's around 75+ degrees out. At night or early morning it's fine.

I'll probably pressure test the cooling system when I have the belts and water pump replaced. On that note there is no noticeable coolant loss nor any white smoke or sweet smell.

 

There was foam sealing the sides and bottom of the OEM radiator. If you did not replace the foam, this exact problem will occur. does not necessarily need to be foam, but something to seal the sides and bottom and force the air through the radiator. Preferably a material that can withstand the temperatures under the hood and not easily combustible. An actual temperature gauge would be a smart investment as well. Had I not had one I probably would have cooked my engine. If the foam is present then look into the items RIWWP mentioned.

 

Good catch kevin, I forgot about the foam lining.

 

Where can I get that foam lining? I know any home hardware has them but will they stand up to the heat?

 

Air pressure is all they need to stand up to, you just need to prevent the air from having an easy path to flow around the radiator. Foam with one sticky side from whereever you get it from is usually used for replacement.

Some people use tin sheeting and fabricate more fixed shrouding.

 

Damn, I just took out that piece of foam under the radiator yesterday because it was torn apart Lol. Good thing I saw this before I decided to drive my car. I'll probably replace it with some garage liner and 3M tape tonight.

Posted From RX8Club.com Android App

 

Check out the $100 thread in my sig. One of the items talks about foam. I just used pipe insulation. Your goal is to keep the hot air from the engine bay from blowing back around the radiator and going through again.

 

Thanks I appreciate it. Your thread has been been very helpful and I've referred to it several times. I ended up using a weather seal foam strip with some 3M 90 adhesive spray. I was trying to find polyurethane foam similar to the OEM material, but no luck finding it at my local Lowe's and for some reason the nearest Home Depot is almost 40 minutes away. ad: I also inspected the foam on the sides and they seem to be holding up pretty well. Hopefully, the foam holds up during really windy conditions.

Posted From RX8Club.com Android App

 

wow been having this same issue, that crappy piece of foam is what it was wow..... cant believe that haha

 

Glad to help..

The airflow in the engine compartment for this car must be something to behold...

 

before checking the insulation you should check to make sure the undertray is still actually there.

8's are popping in here all the time with them missing the undertrays and it's the first thing i point out. it's also one of the most annoying things to see, being in the desert where temps hit over 115F. if you have the car serviced you should be sure it is always reinstalled, they are NOT cheap to replace.