SEARCHED: positive coolant pressure when car is dead cold-what's wrong?
 

I've searched for the past couple days and found nothing so I'm starting a new thread.

I have positive pressure in the coolant system when the car is dead cold. The car has been slowly losing coolant since I took it out of storage a couple months ago. I first noticed the positive pressure a couple days ago when I opened the filler cap (on the water pump housing) and coolant blasted out with such pressure that it blew the cap a good 10 feet away. I topped the coolant off, sealed it up, took a shower, went for a short drive and parked it. I opened it again this morning, after letting it sit 3 days since the last drive, and the same thing happened. The water temp the first time was 23c. I didn't check the temp the second time but the car was stone cold.

I have checked for air bubbling up, indicating an O-ring problem, and haven't seen any. I did notice that after idling the car for 2 minutes without the filler cap the coolant level rose approximately 1 inch and started overflowing. I know the coolant expands as it heats up but it was well below operating temp. The ast was replaced with another stock unit last summer. All visible coolant hoses (rad and ast) appear to be fine, but I'm not sure about the condition of the lower hose. The AST is mounted upright but slightly below the top of the radiator, which is also mounted upright to make room for my FMIC.


Somehow additional air or liquid is getting into the system and is not able to get back out. What's going on here? Is the ast too low? Is air getting sucked into the system when the water pump cavitates?

it needs a motor soon

mike

Is it true that coolant taste's sweet?

Where did you come up with that one?

Is it true that coolant taste's sweet?

Since the AST pressure cap is suppose to vent pressure over its' designed value and also allow backwards vacuum flow, then it must be either defective, or a hoses is pluged. This also applies if you got rid of the AST with the FC type system.

Have you modified the stock cooling system?

I have a PWR radiator mounted upright. The AST is mounted behind the radiator at about the same height, but not above it. I'm not really sure this matters but I thought I'd mention it.

check your rad caps, or running pressure.

AST suppose to be higher than any other parts slightly.
I think the correct working order of it is to have it filled with half full coolant. If its lower than radiator, it may cause problem since it will be full of coolant, thus not releasing any air out...
Its a kind of pressure relief when the air pressure gets too high...

hmm.....I'll see what I can do.

enough pressure in the system to blow off the rad cap 10FT that is not a good thing. any white smoke out the exhaust ?

I think that cewrx7r1 is on the right track with fautly caps and/or hoses. If it is staying THAT pressurized for 3 days without filling up the combustion chamber with coolant, i wouldn't suspect a blown o-ring.

Burning coolant smells sweet but I don't know about tasting sweet...Taste it and let us know :D

:bigthumb: good luck!

Tastes sweet for animals. :D

I'm stumped on this one though. Why would cold coolant have pressure?

I'll help you fix it (go for a joy ride in it). :D

when i first got my car. i said it can't be coolant seals. its gotta be these stupid rad caps.......... yeah it wasn't the rad caps ;)

Thanks for the vote of confidence Vosko;) In law there is a saying "plan for the worst hope for the best. Also applies to RX7 ownership.

Couple things to consider though:
-If it were the o-rings wouldn't the coolant flow INTO the motor rather than air flowing out when everything is cold? I've never heard of it going the other way around. I can't think of a senerio that would cause this to happen.
-no bubbles in the filler kneck when the T stat is closed.
-no white smoke on startup.

1. when they are just starting to go, it will pressureize the cooling system.
2-3. it might not be that bad yet

mike

I was in that situation once. :(

Update: Today I tried to raise the ast by first removing the rubber tab connecting the bottom of it to the frame cross member. As I pulled coolant started squirting out of the line that goes from the bottom of the AST to the radiator. Apparently a sharp seam on the cross member punctured the line. This may have been caused by vibration ect OR I may have done it as I was trying to remove the tank. I'm hoping for the former since the later would rule it out as a possible cause of my problem. That would certainly account for a loss of coolant, but still doesn't explain the high pressure. I'm going to work it through in my mind and hopefully I can come up with something.

just keep an eye on it and if starts overheating shut it down. i drove my car with blown coolant seals for almost 6 months. i carried atleast 3 gallons of water and a few quarts of oil at all times. oh yeah my oil seals went too. man those were the good ol days :D

it seems like there are lots of coolant problems..what do you guys to do "fix" or prevent the problems? mod the system

Replace all coolant hoses. Replace radiator. Replace/remove AST. Replace thermostat. Get better temp reading equipment than stock. Perform some variation of fan mod.

And THEN replace the engine! :)

I spoke to Dave at KDR. He suspects a coolant seal on the combustion side of the block. He said one way to check is by looking at the spark plugs with a magnifying glass to see if there are "little white hairs." That is apparently what coolant looks like on the plugs. Does anybody have more information on this test? -when should I do it? should I let the car sit, start it then check? That seems like the most logical time since the coolant would have a chance to leak into the chamber(s) but wouldn't be completely burned off.

I redid the Champaign bubble test yesterday using the sprite bottle. There were no bubbles present from cold to 82c. To be thorough I decided to watch it cool since my system seems to be pressurized even when the car is cold. I noticed a couple large bubbles during the first 10 minutes. Not sure if that's relevant. Has anybody done this test with a healthy motor?

What other tests can I preform?
-standing pressure test: that seems kinda pointless since my system is able to hold + pressure for days at a time.
-smog sniffer test: is there is a point to doing this if I don't have any bubbles?
-tail pipe test????: is there a precise way to check for coolant in the exhaust besides checking for an odor? I don't trust my nose enough to use it as the basis for writing a $3000 check :p

I know a lot of this stuff has been covered in other threads, but there is not much detailed info. I'm looking for specific instructions.

^