Coolant Flush Help
 

So I'm doing a full overhaul of my car. Ran into an issue flushing the coolant.

I drop all coolant from rad, block, and overflow tank, flush them out with a hose, then rinse with distilled water. Button everything back up, fill the system with distilled water and go to burp it with a lisle funnel.

Start the car, turn the heat on setting 1. Funnel is about 1/3 full, some bubbles coming out, everything looks normal. I notice the temp raising much slower than normal, hanging at around 40c. Eventually it starts rising, and at around 70c begins to rise VERY fast. Things at the funnel are still fine at this point, just more bubbles.

Once the temp gets to around 90c it starts slowing down. Not sure what it would have gotten to, because at this point I look up and see water and steam gushing out of the funnel. Shut the car off and came here. Cooling system had no issues prior to this. Thoughts?

Sounds like you had an air pocket behind the thermostat. An air pocket won't register temp well on a temp gauge so that explains the low temps. When the thermostat finally opened it shot out steam and air.

The thermostat should have a jiggle pin at the 12 o'clock position to allow air to escape when the car is warming up. You may want to check out that thermostat. Some new ones don't have a jiggle pin, if so drill a small hole at the 12 o'clock position.

I just found that Aisin, who makes a ton of OEM Japanese parts, has a thermostat for the RX-7 -

That would be a good way to go or the OEM thermostat. NEVER use a parts store thermostat, I've seen a ton of those fail prematurely.

Dale

Someone correct me if I am wrong, but I don't think you can keep the lisle funnel connected once the water reaches temperature. I also left my funnel connected too long the first time because I didn't think about it.

Nope, you can leave it hooked up while the car warms up - that's most of what makes it so awesome, is it gives a place for air to go and keeps filling up the coolant as air comes out.

A large trapped air bubble just has no hope, though.

Dale

Ah, good to know. I must have just had some air bubbles in there. It always made a mess if I left it on there for longer than 10 minutes or so. Just a coincident I guess, it makes sense the air would come out when the thermostat opens up.

Just went to burp it again with barely any water in the funnel. Temps rose at a normal pace this time. Got to 83c which is normal operating temp. After about 4 mins though, it rose to nearly 100c, and the water in the funnel was nearly overflowing.

Would an air pocket cause the high temps too?

When I'm doing a coolant bleed, I find that running the AC fans to keep the coolant temp just above thermostat opening temperature is enough to get the bubbles out without the funnel spewing coolant everywhere. Remember without the pressure of the cap, coolant will boil below 100c.

It's normal at a certain point for the coolant level to rise in the funnel once it's good and hot. Really, after the thermostat opens and most of the air bubbles are out just shut the car off and let it cool down with the funnel attached. Once it's cool remove the funnel and cap it up. Drive it some and top it off over the next few days/heat cycles. The topping off should just be a TINY bit of coolant typically.

Dale

Welp, I feel pretty dumb. First time doing this with the lisle funnel. I thought you could leave it and the car on indefinitely. Thanks for the help guys.