Is there a cheaper alternative to the "name brand" (NOT Mazdaspeed or other $40 JDM brand) 16 lb radiator caps? I am puking coolant into my overflow while on track.

Also, does the filler cap on the filler neck ever need to be replaced? Mine is just a cap, not a radiator type cap. There is a rubber seal on it, and it is not leaking, but it is not confidence inspiring either.

 

If you are boiling that much coolant, first I'd look at improving my cooling system for sure.

What kind of radiator are you using? It sounds like you aren't disapating enough heat and causing your coolant to boil. I would be wary of using a 16lb rad cap, as that puts quite a bit of stress on seals.

I don't run on the track, but speaking from general automotive experience.

 

It is not boiling over and overheating. The water is just expanding and venting into the overflow. When it cools back down there is an air bubble in the upper radiator hose. It does not overheat even with with this air bubble in the system, but the low coolant light may come on. I just have to pour the excess from the overflow back into the upper hose, and it is fine again. It is not consuming any coolant.

It does not do this on the street, only on track. The radiator and water pump are both pretty new. also the radiator cap is new. All the factory air ducting, undertrays, and fan shroud are still on the car.

Do the fill caps on the engine wear out and/or bleed off pressure?

 

your stock one may have just gone bad and isn't holding at 13lbs and letting coolant by too soon.

i had the same problem and i just replaced the cap and it went away.

and the filler cap only needs to be replaced if it is leaking

 

Simple fix: add enough coolant/water to the overflow so that when it's cold the end of the vent tube is JUST under the surface - then when it heats up the level will rise, and when it cools down it will pull the coolant back into the system instead of air.

 

I already do that.. it never sucks back in.

 

Well filler cap is not leaking, and the radiator cap is new. It was doing this with the old one, so I replaced it. New one does the same thing.

 

umm i gota rad cap from autozone...lol

 

A 16 lb one? I can get a 13 lb one anywhere.

 

it was either 15 or 16. i'll chek and find out for sure.

 

Is the point of the 16lb cap to prevent the coolant from moving into the overflow? That won't work.

You need to pressure test your cooling system.

If the coolant does not return to the system from the overflow tank, you have a leak. Air is being drawn back instead of the coolant.

The leak could be anywhere, but most likely places are any fittings you recently removed and replaced. Also, the hose from the rad neck to the overflow can leak air back in. Heater hose connections, water-pump seal, even a leaking heater core can be the culprit.

Pressure up to around 30 psi with the pressure test. The pressure test will find the problem, unless it is in the overflow tube.

Or, you could just switch to Evans Cooling NPG+ and convert to a no pressure system.

 

That was my thought but there is no leak that I have seen, which is why I suspect it is the filler cap. I will take it and get is pressure tested. I still want the higher pressure cap though.

 

There is a leak. You just haven't done enough to find it.

The higher pressure cap won't do anything for you. The increased pressure might find your leak. Ok, it will raise the boiling point of your cooling system a few degrees, but boiling point is not your issue. Your issue seems to be coolant return.

If you want high boiling points, switch to Evans Cooling. Your boiling point will be 375*f. You can pop out the little check valve in the center of the radiator cap to create a 'no-pressure-cap'. Your system will now likely NEVER boil and the coolant will ALWAYS return from the expansion tank.

Summer of 2008 while driving on the Central Expressway in Dallas on a 100*+ day, I broke a fan belt. It took out all of my belts. I heard it pop and slap. I watched the needle go strait to the top of the gauge. There was no shoulder, heavy traffic and the Forest Lane exit was about a half mile away. I drove to the exit and parked in a parking lot. The needle on my S5 had been PEGGED for most of that drive. I let it cool for awhile and rolled the only viable but damaged belt belt back on. The air pump belt. Found an Orielly's Auto on my GPS. Half way to the Orielly's, that belt turned it's last and broke. I drove the rest of the way, certain that the engine was toast. I bought new belts and installed with borrowed tools.

https://www.rx7club.com/showpost.php...35&postcount=6

No problems, no damage, no boiling. Nothing spewed out over the overflow. Literally *no* consequences (other than buying a homeless guy a bunch of hamburgers to keep the other homeless people away while I worked on the car). Evan's Coolant saved my engine that day.

Evans Coolant NPG+ is about an 85% Propylene Glycol and 15% Ethylene Glycol mixture. You can 'try it out' by adding 85% Prestone No-Tox and 15% regular Prestone to your system. Completely drain the radiator, the bottom of the block etc. to remove all traces of your old coolant. You want ZERO WATER at all in the mixture. Don't run this homemade mix for very long. The anti-corrosion additives are not designed to be used in the absence of water.

If that trial works out, buy some Evans Coolant NPG+ .

 

Sorry to ask this in your thread OP, but the Prestone No-Tox you are talking about it's the animal safe prestone correct? I see using this mixture is not safe for long periods, but I am assuming the Evans Coolant is safe for everyday use correct?

 

I think your problem is with Coolant cavitation in the waterpump and not the cooling system's cap..
have you thought about an Underdrive pulley system to Slow down the Pump?

 

Yes, I wrote No-Tox but actually it's Lo-Tox.

The 'home made' mix is safe to use for an evaluation period, couple of months?


Evan's NPG+ is the correct stuff for everyday use. It is considered a 'lifetime' coolant by Evan's. It is what I use. There are quite a few FD guys using it as well.

 

you can get a 16lb cap by going to kragen or autozone and asking for a radiator cap for an FD, most aftermarket suppliers have it listed as a 16lb cap because the aftermarket ones don't hold at 13lbs very well in a rotary engine environment.

 

i don't recommend a 16lb cap as it puts more stress on the coolant seals of the engine.

there's something wrong with your cooling system, fix the problem instead of putting a bandaid on.

 

I got a pressure testing kit today. Hopefully one of the 8 attachments fit my radiator.

I have no need to go NPG+ You are kind of stuck if you ever have a problem on the road or track and don't carry extra. I have used it before in another car and was not impressed for the extra money.

Also, I don't have a overheating problem, I have leak or component problem. Presumably, when I replace the faulty component, I will no longer have this problem.