The case of the lost coolant
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From: new york
The case of the lost coolant
I have a 94 FD. I bought it about a year and 1/2 ago. Every now and then,(about every 600 miles) my coolant buzzer would come on. I would let it cool down and I would be missing about 1/2 a gallon of coolant. It has Gotten to the point that this happens every 50 miles. After many tests. it appears that the engine is building up pressure ( not over heating) and pushing the coolant out and into the overflow tank. I was wondering if this means a rebuild? (car runs great) Or a fixable problem other than engine rebuild? and if it means rebuild who is good in the north-east?
Thanks
Dave
Thanks
Dave
https://www.rx7club.com/showpost.php...6&postcount=51
https://www.rx7club.com/showthread.p...rflow+pressure
First, I'd replace the caps to cover the simple and easy stuff.
Rent an Autozone coolant pressure tester and try pressure testing the system and to test the caps.
Also do the champagne bubble test and/or have your coolant tested for combustion gases. (Champagne bubble test = remove the filler neck cap on a cold engine, insert a funnel or inverted 2-liter bottle full of water, and start the car. Let it get warm - once the thermostat opens, a steady stream of little bubbles suggest combustion gases leaking past a bad engine coolant seal).
Dave
https://www.rx7club.com/showthread.p...rflow+pressure
First, I'd replace the caps to cover the simple and easy stuff.
Rent an Autozone coolant pressure tester and try pressure testing the system and to test the caps.
Also do the champagne bubble test and/or have your coolant tested for combustion gases. (Champagne bubble test = remove the filler neck cap on a cold engine, insert a funnel or inverted 2-liter bottle full of water, and start the car. Let it get warm - once the thermostat opens, a steady stream of little bubbles suggest combustion gases leaking past a bad engine coolant seal).
Dave
Last edited by dgeesaman; Jul 18, 2005 at 09:30 AM.
Joined: Feb 2001
Posts: 4,000
Likes: 379
From: Aurora, Ontario, Canada
A friend of mine (Charr33) and myself have recently gone through this situation.
In both our cases it turned out to be the engine needing a rebuild.
Do the simple stuff first (check the caps.. etc.) but chances are good you'll need a rebuild.
Sucks to hear, but I think it's time... I have a 94 as well... 132k on the clock on the original engine...
Lates,
In both our cases it turned out to be the engine needing a rebuild.
Do the simple stuff first (check the caps.. etc.) but chances are good you'll need a rebuild.
Sucks to hear, but I think it's time... I have a 94 as well... 132k on the clock on the original engine...
Lates,
Here is one simple thing to try first: Sometimes the hose that runs from the neck of the AST to the reservoir tank does not seal properly at the AST nipple.
Normally, overflow coolant goes out of the AST to the res tank when the system is hot, but the coolant can't return when the engine cools down if the hose leaks and sucks in air instead of drawing coolant from the res tank. Inspect this hose to see if it leaks, and try putting a hose clamp on the hose at the AST nipple.
Normally, overflow coolant goes out of the AST to the res tank when the system is hot, but the coolant can't return when the engine cools down if the hose leaks and sucks in air instead of drawing coolant from the res tank. Inspect this hose to see if it leaks, and try putting a hose clamp on the hose at the AST nipple.
RX7 lover
Joined: Jun 2005
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From: UK
If you are not seeing coolant in the exhaust on cold starts (a white, sweet smelling plume), and the amount of extra coolant that shows up in the overflow tank approximately equals the amount you have to add to the top up the filler neck on the engine, there is nothing wrong with the engine. It is just a failure of the coolant return system (the pressure cap on the AST and the hose that runs from the neck of the AST to the overflow tank).
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Joined: Jun 2003
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From: Edmonton Alberta Canada
I post this again as there are so many who panic when coolant overflows or exits the engine.
Think of the engine as a coolant pump to and from the overflow bottle. When the engine warms up the coolant expands and forces its' way past the cap with the spring, through the overflow tube into the overflow bottle. When the engine cools down it creates a vacuum, which sucks coolant back from the overflow bottle.
This works fine until one of your coolant caps develops a vacuum leak at the rubber seal. Then all that happens is some percentage of the coolant in the engine is pumped into the overflow bottle and remains there, leaving the engine a little low. This allows the pressure to drop after shutdown (because air is compressible), which in turn allows the coolant to boil after shutdown. The metal in the engine holds a lot of heat when the engine is running, and this is ok as long as there is coolant flow to carry it away. Once the flow stops, the coolant will heat up more than normal, and if the pressure is low enough, it will boil.
The classic event run is you notice the engine coolant level is way down (checking when cold, of course) when you look in the water pump fill tube. You pour in more water. It gets pumped into the overflow bottle (to stay as you have a vacuum leak and can't get it back to the engine). You are now nervous, and check the level in the engine every day (morning when the car is cold), and fill it. Soon (two to three days) the overflow bottle is full to the top and leaks out where the filler tube (removeable) joins the bottle. You see the puddle and panic.
It happened to me. Solution - replace both caps (they were old), replace all small coolant hoses to/from overflow bottle (they are not designed for pressure use as there is no pressure in this part of the system, so they are thin and can be collapsed under suction - stopping the coolant from returning to the engine. I replaced them with suitable pressure coolant hose routed so it would not kink (it's thicker so care must be taken when routing it - it will not bend as well).
You may have an engine problem, but this is where you should start as others have said. Hope this solves your problem.
Think of the engine as a coolant pump to and from the overflow bottle. When the engine warms up the coolant expands and forces its' way past the cap with the spring, through the overflow tube into the overflow bottle. When the engine cools down it creates a vacuum, which sucks coolant back from the overflow bottle.
This works fine until one of your coolant caps develops a vacuum leak at the rubber seal. Then all that happens is some percentage of the coolant in the engine is pumped into the overflow bottle and remains there, leaving the engine a little low. This allows the pressure to drop after shutdown (because air is compressible), which in turn allows the coolant to boil after shutdown. The metal in the engine holds a lot of heat when the engine is running, and this is ok as long as there is coolant flow to carry it away. Once the flow stops, the coolant will heat up more than normal, and if the pressure is low enough, it will boil.
The classic event run is you notice the engine coolant level is way down (checking when cold, of course) when you look in the water pump fill tube. You pour in more water. It gets pumped into the overflow bottle (to stay as you have a vacuum leak and can't get it back to the engine). You are now nervous, and check the level in the engine every day (morning when the car is cold), and fill it. Soon (two to three days) the overflow bottle is full to the top and leaks out where the filler tube (removeable) joins the bottle. You see the puddle and panic.
It happened to me. Solution - replace both caps (they were old), replace all small coolant hoses to/from overflow bottle (they are not designed for pressure use as there is no pressure in this part of the system, so they are thin and can be collapsed under suction - stopping the coolant from returning to the engine. I replaced them with suitable pressure coolant hose routed so it would not kink (it's thicker so care must be taken when routing it - it will not bend as well).
You may have an engine problem, but this is where you should start as others have said. Hope this solves your problem.
Originally Posted by Retserof
Here is one simple thing to try first: Sometimes the hose that runs from the neck of the AST to the reservoir tank does not seal properly at the AST nipple.
Normally, overflow coolant goes out of the AST to the res tank when the system is hot, but the coolant can't return when the engine cools down if the hose leaks and sucks in air instead of drawing coolant from the res tank. Inspect this hose to see if it leaks, and try putting a hose clamp on the hose at the AST nipple.
Normally, overflow coolant goes out of the AST to the res tank when the system is hot, but the coolant can't return when the engine cools down if the hose leaks and sucks in air instead of drawing coolant from the res tank. Inspect this hose to see if it leaks, and try putting a hose clamp on the hose at the AST nipple.
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