I've been having an ongoing battle with my coolant buzzer coming on and then going off once the car reaches normal operating temps. The temp needle has NEVER gone past half way.

Originally the AST was eliminated by the previous owner. I just installed an aluminum AST to eliminate the "air in system" possibility of my problem. I also replaced all hoses that run to and from the AST with new ones. There are no coolant leaks.

When the engine is running with the filler cap off there is no sign of the bubbles that would indicate a bad engine seal. Compression is 90psi in each chamber and the plugs look fine. Every now and then there is some white smoke at startup, but it does not smell like coolant.

I am pretty sure that the problem is that coolant is not being sucked back into the system from the overflow tank - which would explain why the level is fine once the car is warmed up and the coolant has expanded.

Once the car cools off and I remove the filler cap there is a suction effect, which makes me think that the problem is with flow from the AST to the coolant system. If there was a problem with an engine seal, I don't think that there would be a vacuum in the coolant system after sitting for a few hours.

Could bad caps be causing this problem? Right now there are 3 in the system, all of which are spring loaded (one on the radiator (I think, I've never seen it), one installed on the filler neck for the AST elimination, and one on the AST).

Right now I am thinking that it may be a problem with the overflow tank itself, perhaps something in the bottom of it that covers the straw up and prevents the coolant from being sucked back into the system. Has anyone had a problem like this? What do you guys think?

Thanks,
-Charlie

 

my buzzer used to go off on occasion and there was adequate coolant in the system. i had rebuilt my entire cooling system with new radiator, hoses, clamps, ast, water pump, and thermostat but had minor leaks somewhere. after a few months, a couple of the hose clamps required tightening because of seapage and a hose going to the top of the overflow/fill reservoir needed to be re-seated. finally got all leaks taken care of and still the buzzer would go off occasionally and then stop. the problem i was having was due to a poor internal connection in the sensor due to corrosion. jiggled the wire and it stopped buzzing. took me a while to isolate this problem. 1. check your sensor.
2. also, have you "burped" your system?
3. another thing - dont rely on the stock temp gauge. get a gauge that works in a linear mode with a numbered readout (0-250degree for example).

chuck

 

Chuck,

Thanks for the response. To answer your questions...

1. I have replaced the sensor (the old one was leaking around the edges) - I don't think there is a problem with the sensor because I have to add coolant to top off the level, so there is actually a problem with the level.

2. Yes, this problem has been going on for months and I have been topping it off all along with no luck. I just installed the AST in hopes that if there was some giant air bubble causing it, it would fix the problem. But no dice.

3. I've thought about getting a better temp gauge but I'm not sure what is involved in installation, is it as simple as splicing into the wire going to the existing one?

-----

Is it possible for a pressure relief cap to go bad so that it doesn't leak under pressure, but leaks air into the system under a vacuum?

Thanks,
-Charlie

 

In a word, yes. If the outer seal is bad, it will do that. The inner seal holds the pressure, but the outer needs to seal tightly to draw the coolant back. However, if the coolant doesn't get drawn back, the O-F tank would gradually overfill if you continued to add coolant.

The other possibility, as you have mentioned, would be a complete blockage of the line. If the line were completely blocked, then coolant would leak out somewhere between the cap and the blockage. In this case, you might see the coolant hoses collapsing under vacuum when the car cools off.

If the O-F tank is not overfilling, and there are absolutely no external leaks, you could still possibly have a marginal coolant seal that only lets a small amount of coolant into the combustion chambers while you are running.

On the subject of coolant gauge wiring, no, you can't depend on the original sender being compatible with an aftermarket gauge.

 

There are plenty of threads about aftermarket water temp gauge install. The way I would do it today is the throttle body coolant line install.

Very easy to do.

 

The cap on the filler neck should not be spring loaded. That cap may be keeping coolant from getting to the AST.

To remove the air from your system, remove the throttle body coolant line. Fill the AST until full, and wait to see if it goes down. Fill more as needed. Cap the AST, and fill at the filler neck. Keep an eye on the TB coolant line during this. If coolant starts to come out, reattach it. When you are done, be sure to clamp the TB line.

This should eliminate ALMOST all of the air in the system. Test with your new filler neck cap.

 

Adam C, right on - I didn't notice he said the filler neck cap was ALSO spring loaded.

 

I had a problem that sounds similar to your mysterious antifreeze loss. In my case the radiator-end hose clamp on the upper radiator hose developed a small leak a long time after I replaced all the hoses. It took at least 2-3 months for it to show up and because it had been so long I suspected all kinds of bad things before I finally stumbled on the the cause.

Like charliegt I never had any appearent problem or overheating while driving, I couldn't find any evidence of antifreeze under the car after being parked overnight, and there wasn't a lot of white-smoke at startup. But about once every week or so the low level alarm would go off and each time when this occured the collant level in the engine was indeed low. However, in my case the overflow tank level would be low, too.

On my car I had previously added two additional openings in the bottom on the stock air box for less restriction (which by the way works great http://www.rx7.org/Robinette/coldair.htm ) and the small amount of leaking antifreeze was being sucked back in to the intake; hence the lack of evidence.

Obviously this turned out to be a super easy fix; reposition clamp and tighten more securely, and then replace the the paper filter element which was by now about 25% saturated with antifreeze. Part of it was still wet after several days of setting!

 

How many miles since last rebuild?

 

I would suspect the AST cap and the filler neck cap. Be sure they are new(about 7 bucks each) and that they are both rated for the same pressure. IE, don't have a 13lbs filler cap and a 9 lb AST cap etc.
Art

 

Ive had a handful of coolant problems in the past... this is what i would do..

check your ast output hoses to make sure they are not kinked.. any kinking and you will lose coolant from your overflow tank

run the car at like 2000rpm while you fill up coolant and then check carefully with a flashlight for any small leaks, make sure that your hose clamps are tight after you installed your new hoses (especially turbo coolant hoses)

if you still lose coolant, then replace your radiator cap

chris

 

Hi charlie,
I have exactly the same problem on my 98 FD,I've replaced radiator caps with brand new ones but still no fix and like yours no external leaks and cant explain why coolant from reservoir cant get sucked back inwhen theres vac when you take the cap off.Tried sucking on reservoir hose (got that DESPERATE)doesnt seem to have any blockage.Just about driving me mad!!!If you find a FIX please PM me and you can stay with me for free if you ever holiday in New Zealand.

cromwell

 

get a pressure tester, pump it up and start looking.

 

 

on my car when filling with throttle body coolant hose disconnected, water will come out of the throttle body coolant nipple before it comes out of the hose, do you guys cap the throttle body coolant nipple when filling with the hose disconnected?

 

Alright guys, thanks for all of the help. I was going to wait a few days to post this but since this thread got bumped back up I might as well post an update.

It appears that the problem MAY be solved. I don't want to jump the gun, but I haven't had to add any coolant over the past 3 days and no buzzer. When I check the level sometimes it is right at the top of the AST and sometimes about half way down - which makes me wonder if it is fixed or not - but since the system apparantly seems to be sucking enough coolant back in to prevent the buzzer I'm optomistic.

I think that installing the AST fixed the problem (possibly because air in the system was the problem, or maybe because the spring cap on the filler neck wasn't working properly) and that I just needed to top it off once or twice to get the system filled up again - since when I installed the AST I replaced all of the hoses that go to it, most of the coolant drained out when I disconnected the one that goes to the bottom of the radiator.

As far as leaks go, I've found and fixed the following over the past 2 years :

- The upper radiator hose developed a slit from the airbox pressing down against the edge of the fluidyne radiator that I have.
- The hose clamp that holds the upper radiator hose to the thermostat housing cracked and was letting coolant leak out.
- The crappy coolant level sensor corroded enough to let coolant seep out around it, had to replace it with a new one.
- The screw-style hose clamp that I used to replace the spring loaded one in part 2 needed to be re-tightened.

At this point there are no leaks that I know of. Also, there seems to be vacuum in the system when I remove a cap after cool down to check the level.

The line running to the overflow tank seems to flow freely, when I blew in the end of the hose I heard bubbles - however when I sucked I got a mouthful of cooland and didn't continue, so I haven't ruled out the possibilty of something in the overflow tank getting pulled to the little straw that retreives coolant and preventing it from being sucked out.

I'll post an update once I have more time to drive it and make sure the buzzer is gone for good.

Thanks again to everyone who helped out,
-Charlie

 

I spoke too soon. Checked the level this morning and it was near the bottom of the AST - and overflow tank was nearly full... I am pretty certain that the problem is either a bad cap or a hose clamp. I plan on going over all the hose clamps again with a wrench, and replacing the spring loaded cap on the filler neck with a normal non-relief cap. I'm also thinking about taking out the overflow tank and checking it for anything that may be clogging the return straw.

-Charlie