I've seen a lot of articles on Coolant leaks, but I have yet to see one that resembles my issue, so here goes.
'87 FC, NA, 5sp.
As the engine warms up the engine some fluid will make its way into the tank. Nothing spectacular, never hits the top of the tank. All normal.
Now the problem. It doesn't return. As the engine cools, the fluid stays in the tank and the next time I start the car, I get the engine coolant alarm. So "air" is getting in to the system. When the engine is cool, removing the cap seems to release presure (fluid around the seal blows outward when the cap is removed, I would suspect a vacume situation would suck anything near the seal inward.)

Possibilities:
Rad cap, It's holding presure, and the return is easy enough to move by hand. Doesn't explain the air in the system when cool.

Seal, No billowing white smoke, I'm not loseing coolant, I can take what's in the bottle, return it to the system and I don't have to add any more. Also not getting air bubbles at the holding tank with the engine running, and when I turn the engine over with the cap off, I'm not geting excessive fluid pushed out of the filler.

The holding tank cap/straw is drawing air - If it was sucking air into the system, the system should be nutral when I remove the rad cap.

If I were loseing fluid I would understand, I'm gaining air w/o any odd fumes in the coolant system. Is there anything that would put presure/air into the system, but not lose presure during cooldown???
Thoughts? Ideas?

 

There are lots of threads about this, but they are relatively hard to search for due to the complexity of the issue.



You have a leak somewhere. This leak allows the cooling system to suck some air in instead of coolant back from the over-flow tank.

The solution to this problem can be very elusive. Here are some my suggestions:

The first place to start looking is the small tube between the rad neck and the overflow tank. Pressurize and listen. I used a blow gun with the rubber nozzle on my air compressor put against the overflow tank overflow tube. I set the pressure for ONLY 10 PSI at nozzle.

If that doesn't leak, then you may have a leak somewhere else. It is possible that a previous owner put in some Silver Seal, Barsleak, or some other 'hope-in-a-bottle' type crap. You can have a leak that holds pressure but does not hold vacuum. Try using a cooling system pressure test kit. That kit is available to 'rent' for free an many parts stores. This may or may not find the leak.

I found my finally in a tiny crack in the S5 thermostat neck. Other places include the seal of the thermostat neck to the waterpump housing, the seal of the waterpump housing to the block, the waterpump shaft seal. Look for telltale signs of water or coolant deposits running down the front of the engine. They will have some white crusty deposits, looking like dried up tears.

The solution to this problem can be very elusive. Be patient, systematically eliminate the possible leaks. Eventually you will solve this problem. Along the way, someone is going to tell you that you need to rebuild your engine. Don't listen to them.


Good luck!

 

Possible caues:
1. Tiny hole in return hose, or other leak somewhere in the cooling system keeping a vacuum from forming.
2. Clogged return hose. Remove and unclog it.
3. Too much coolant in the system already. Like if you have a different problem like #4 and you keep adding coolant to the radiator cap to stop the buzzer. Whenever topping off the radiator, drain the coolant reservoir to "Low" line to accept the excess from the radiator.
4. Too much air in the system. Air bubble hits the coolant sensor and you get a buzz. Try closing all caps and pulsing a hose to get the air to the top, them refill. This is a lousy method to remove air, btw. If this seems to help a lot and you're not just imagining it, get a Lisle funnel and do it right. Do a search for "Lisle" for more info.
5. Blown engine coolant seal forcing exhaust into the coolant (eep, better hope not). Look up a guide and carefully diagnose first before assuming something so bad. This is the "rebuild your engine" nonsense jackhild is talking about.

 

Thanks for the tips guys. Much to test and search....

Today I was able to perform the folowing test...
Once my engine cooled I took off the rad cap and put it back on. (nutralized pressure)
I used my air compressor to apply a small amount of presure to the spill line form the holding tank. The tank presureized, the lid to the tank didn't hold presure. (expected). but no fluid moved into the rad. (positive presure from the overflow side of the rad cap should simulate a vacume in the system.)
I removed the overflow line from the tank and applied about 25 lbs to the line. The rad cap didn't open. I removed the cap, flipped the center valve by and and put it back on, now the air flows in. Suspect the cap is bad.

I removed the bleader bolt from the rad, re-attached the overflow line to the tank and applied presure to the spill line. I was able to fill the top of the rad and put the bolt back in. Question about the bleeder bolt. The rubber is craked in several places. I'm not seeing any coolant coming out when the system is running, but could this be a poblem spot? I might as well replace it.

I let the engine cool down for a few hours. Turned it back on w/ the rad cap off and watched the fluid flow. It looks like the thermostat is stuck open. At start up (not warmed up) with at 1k+ rpm the fluid is running below neck, when the rpm drops the coolant pushes out the top of the neck. Makes me wonder if the impeller on the water pump isn't having issues as well.

After about 2 hours of running the engine I did notice some vapor coming up from the front. It didn't smell like anything. (which bugs me more then if it did smell like coolant). I don't see any white calcifications on the engine, but below the water pump looks like it has been wet. I suspect a water pump replacement might be in order. If I'm going to pull the front of the engine apart, is there anything else that should be pulled/updated/replaced while I'm there?

 

I just had this, turned out one of my housings was cracked around the spark plug holes :o

 

Damn, and I bet a tube of JB Weld isn't going to fix it. My wife is already unnerved that I baught a project car, she'll flip if it even looks like it's going to turn into a money pit.

 

Last night I head out to AutoZone to "borrow" a coolant system presure tester. Get home, open the box, test the rad cap... It's a POS, doesn't hold a lbs of presure. (that's an easy replacement. This morning I go out to test the rest of the system. search the box.... WTF, they don't have an adaptor to fit our tiny filler neck (Actully, their tester only first ONE size filler, but has adaptors to test 4 different sized caps.. WHY????). I figure they should have an adaptor back at the store to make it fit. Nope, went to another store, nope.


My question to all of you gurus, where do I find a presure tester for my FC?

 

Presumably your new rad cap will stop this from happening because it is decidedly not "normal".
There shouldn't be enough pressure to overcome the cap during warmup- or even normal running.

 

That would make the $8 cap the best investment I've ever made!

 

I just rented a pressure tester today at Advance Auto Parts for my car. It's a big kit with a gazillion adapters so they wanted to hold somewhere around $150 to rent it (which is the retail price of the kit). The guy let me just leave a card with them instead of doing the whole charge and refund deal. It came in a big black case and I think I used the #9 adapter, but that is completely off the top of my head and could be wrong. It fit like a glove though (I have a Fluidyne rad)

 

The only kit two different Auto Zone's on the west side of Indy would rent me was an $80 set that only had two adaptors. Each for testing rad caps. The ONLY connector they had to connect to the collant system was the one at the end of the presure pump. Looks like al AZ's are not* created equal. I will have to call around to see if any of the other local shops has a different kit.

Thanks!

 

Advanced is definetly the place to go for the tester. #9 is the right adaptor for the system test. 13 lbs / .9 bars. It's ~$187 to rent the tester. The kit I picked up is missing a rubber O-ring to test the rad cap, but when you consider a cap is only ~$7, if you question it, replace it.

 

Update - My presure tests went well - for a cold system. Held 1 bar for over an hour. (yes, I went a little higer then the cap is rated for.) I only found one leak, lower rad hose, the OEM spring clamp wasn't holding tight enough. Replaced w/ hose clamp.

Now I should give you guys a little background on another issue I belive is related. (you may have seen the following information posted in another thread) -
My cat was replaced by prior owner w/ some POS to improve horse power. Unfortunatly it clogged. The clogging resulted in massive backpresure and heat build up. Untill I get the replacement cats, I've been drilling small holes in the existing unit to release presure. This has resulted in improved HP, RPM, and a cooler runing engine. I suspect when I replace the cat I will see substantial improvement.
When I took the car out for a run last night it ran much cooler then prior runs. After about 20 min I pulled into the driveway, let her continue to idel at about 1800 rpm to keep the fan spinning. After about 2 min of sitting still the coolant alarm went off, so I shut down the engine immediately and poped the hood. The area around the lower coolant hose is dry (where I repalced the clamp) and the area around the water pump is dry. There is no smell of anti-freeze, and the holding tank is just above the high mark. but there is vapor/smoke or some sort coming up from what apears to be the underside of the front/ passenger side of the engine.. I can not poinpoint an exact source.

Out of curiosity, is there a kit to auto-bleed a system of air? I know several cars w/ auto vents to remove the air, but I have not seen a retrofit / kit that could be adapted for other cars.

 

And the saga goes on. I can drive my car about 10 min before the temp goes balistic. I stop, the coolant alarm starts to scream. The over flow tank is full, and I can hear boiling. I've recently replaced the rad cap with one ofthe quick release levered caps. When I gingerly pull the lever, I can tell only air is pushing into the overflow tank.

SO, I've got a few possibilities in mind, but want to get some oppinions on my cheapest option....
Water pump. What are the chances the seal is bad in such a way to allow it to draw air in and not let coolant out? I MUCH prefer this problem over a crack or warp in the houseing.

 

try going to napa and get a block test kit. basically this can test to see if you have exhaust in your coolant. i was stuck where you were earlier in the spring. turned out it was my coolant seals..good luck

 

There is another potential leak location that can be hard to spot...the heater core.
Worth checking out if all else fails.

 

I'll check this one out, thanks!!!!!


I thought about that. I've had the floor cover off to get to the ECU and everything has been dry. If it's the core, I'm not seeing where it's dripping, and on high heat there is no smell of anti-freeze from the vents.

 

Hey TM, do you have to buy one of those block testers or can you rent them as well? I have a problem with my 88 vert over heating when going up hill and I suspect the coolant seals because I ATF'd the engine to get her unseized.

 

Make sure you have the hose routed the correct way to the reservoir. If you had it running to the wrong port on the resevoir it would push coolant in but not suck it back out.

Seems stupid, but I made that mistake once before.

 

you can take it to a shop and have the coolant tested for hydrocarbons.


After the car gets hot and is pushing the coolant into the reservoir, if you let the car sit for a minute or two do you have a hard time getting it to start back up until you relieve the pressure on the radiator?

I had these same issues. car held pressure, replaced the thermostat, hose to the overflow, cap, yet still would get pushed into overflow. took it to a shop, they ran the hydrocarbon test and within 10 seconds I knew.. coolant seal had failed me.

 

[QUOTE=Unsupa;10101318]After the car gets hot and is pushing the coolant into the reservoir, if you let the car sit for a minute or two do you have a hard time getting it to start back up until you relieve the pressure on the radiator?
QUOTE]

The car typically starts right up.
I'm replaceing the water pump in a few hours. If that doesn't solve the problem, the car will need to find a new home. The wife is tired of it being in the garage/driveway and not being used.

 

i hate to tell u but it is a money pit

 

Recently I have gone through everything on my FC for the exact same issue, it turned out it required me going to Mazda and getting an OEM thermostat. Sure enough when I took the old one out it was one of those stant thermostats. It is still running a little on the warm side but I am sourcing a underbelly pan and fan/fan clutch/fan shroud as I got one of those FC's that had the coolant system replaced with aftermarket everything and a terrible e-fan. Hope all goes well and you will get to keep it.

~Spike~

 

I'm doing fairly well.. only $600 in parts over the past year. The water pump is the last non-cosmetic part I'm buying for it. The problems this poor car is having are all* related to the prior owner having replaced the cats. Had I known the aftermarket cats were such POS, I would have started by replaceing them and would have saved myself a LOT of hassle. I stil had to replace the water pump, but would have saved a lot of time making other adjustments trying to overcome the ill effects of a cloged cat.

 

before you buy another pump try taking the thermo out take it inside get a pan fill it with water boil said water and put the thermo in the water. it should open