coolant overflow leak question
 

hello guys, so i'm shopping for an FD and the owner told me the only problem with his car is that when he shuts it off, the coolant flows out the overflow tank onto the ground. now he told me it's because he put in a koyo radiator but he hasnt replaced the stock thermostat so he's telling me that by putting in a lower temperature thermostat its going to fix this problem. does this sound plausible? now i'm no expert in rotaries so i need your help to see if he's bullshiting me or what. :icon_tup:

The overflow is there to collect any coolant that is displaced as the engine comes to tempature and the cap opens up. When the cap opens up it allows coolant to flow into the overflow.

When the car cools back down the coolant should be getting sucked back into the engine by vacuum. If his overflow keeps filling up and never gets sucked back into the engine he could have a pinhole, or leak in the overflow hose.

He should replace the hose and see if it corrects the problem.


The stock thermostat is the only one you should use.

i had that issue with my car and the culprit was a broken overflow tank! I replaced that and put in a new stock thermostat and it was fine!

Have the car run and get hot! my car was overheating and that would cause the issue aswell. make sure its not running hot! if it runs hot and overheats he might be trying to sell you a car with a blown coolant seal!

As far as I know, there are three things that could cause this. It is (hopefully) either the ast pressure cap that has worn out (if the air separator tank (little black plastic tank by the battery is deleted, there should now be a pressure cap on the filler neck which would be the thing to check instead) or a pinhole or crack in the line that goes from the mentionned tank (refered to on here as AST for air separator tank) to the overflow itself.

The very last cause, which i doubt it is, would be blown coolant seals. However, this being the case, the car would have a lot of sweet smelling, white smoke coming out the exhaust and it would be constantly overheating.

I know you said you were overheating but that is more likely just air pockets (from air in your coolant - if coolant is leaking, there must be something occupying the volume of the missing coolant - air. With a lower specific heat capacity, if an air pocket builds around the thermostat it will read a much higher temperature even though you may not be over heating. HOwever, you have to be very very careful with these air pockets. With less coolant, the cooling system is obviously far less efficient making the car very prone to overheating and coolant seal failure meaning a whole engine rebuild.

I guess one last thing as mentionned is that there could actually be a crack in the overflow tank itself.

To check the tank you'll have to jack the car up, remove the passenger side wheel (assuming its a usdm car) and then squeeze in there. I think there is 3 bolts holding it on, and then the top part with the line that goes to the ast just pops off. This would be a good time to replace the coolant line from the ast to the overflow tank. Unfortunately i don't have any ideas how to be certain the overflow doesn't have a crack and it could be quite costly for a new oem one. But if you took it out, filled it with water and let it sit over night and theres a pool around it in the morning, that likely has something to do with the issue.

It might seem like alot do do while buying a car and the seller may not entirely approve but its the only way to know for sure. And coolant leaks are not something to take lightly.

Let me know if you have any questions:nod:

Not to put you off but my car did the same thing, I tried to find the problem to no avail. Ended up pulling the motor and the coolant seal had blown out. I would make sure the problem is stopped if it is one of the above posts first, so you don't end up with a stuffed motor.

Nothing about the radiator should cause the overflow tank to overflow. And nothing about the t-stat would fix it.

As mentioned above, when coolant is heated by the engine it expands into the overflow. After shut down and as things cool a natural vacuum SHOULD form to pull the coolant back in. If that natural vacuum is lost for any reason..leaking hose(s), bad cap, engine coolant seal...coolant is stranded in the bottle and eventually it overflows.
It could be something as simple as replacing a cap or as complicated and expensive as rebuilding the engine. Either he's really stupid or he's bullshitting you.

Other signs of coolant seal failure are stumbling idle on COLD start-up, steam (white smoke) in exhaust, smell of coolant in exhaust on cold start and spiking temps due to air pockets in the system.

thanks everyone, i really appreciate your insight. i'll definitly check the things mentionned, i really hope its not a blown seal.

i'm gonna buy 2 new caps (rad and ast) and head out to see and test the car tomorrow. just a question though. which needs the pressure cap (with the spring on bottom) and which doesnt? i believe AST has the regular cap and the radiator filler neck uses the pressure cap. am i right?

bad motor, don't buy it.

The AST has the spring loaded cap.. The filler neck (not on the radiator) has no spring. How many miles on the engine?

60k miles on the engine.

With 60K on the engine, there is a very good chance that the coolant seals are bad. If they are bad, its time for a rebuild. Even if they are not bad right now, its likely they will fail in the not too distant future. A rebuilt engine will cost several thousand dollars, maybe more if the turbos are in bad shape too.

If there is a rotary specialty shop in your area, I would have them look at the car.

IMO, the current owner knows the coolant seals are done which is why it's for sale. Rarely does an owner put his/her FD up for sale which is spewing coolant out of the overflow tank and not know what's going on.

My experiance in buying my FD is similar to yours. I did all the research suggested by this forum before checking out mine. I was told by the owner there's a little smoke when the car starts and there was, but it didn't seem like an excesive amount at the time.

Well...after a while things started getting worse. My car started having the overflow tank spill problem like you're describing. The previous owner had replaced the overflow tank, which should have told me something to begin with. I replaced both caps but it didn't do anything.

To make a long story short, my car is just about done getting rebuilt. If you decide to buy that car, be prepared to drop some cash on a rebuild. Your luck might be better then mine, but the symptoms your describing ended up with a rebuild for me.

i'm just back from checking the car. the symptoms are exactly as i described. the guy arrived, shut the car off and i started seeing coolant leaking under the overflow tank, but the strange part is that it was spewing from somewhere i couldnt see, it wasnt from the top. i also heard coolant boiling but the car doesnt overheat. another thing i wanna add is that once the coolant stopped dripping, the overflow was still filled to the max.

im gonna ask him to reduce the price by at least 2k to cover the cost of rebuilding.

Mine leaked from the connection going to the AST, not the filler cap. And mine made all those same sounds and was still full.

You don't have the experience to do the rebuild yourself and there are alot of things that are smart to replace and upgrade during the rebuild. Not to mention the down-time and inconvenience. And in all likelyhood he lied to you about the cause of the coolant on the ground.
Ask him to reduce the price by at least 3.5k or look for another car.

2K won't cover the cost of a rebuild.

$1k would barely cover the cost of new apex seals, coolant seals, oil rings, bearings and gaskets. And that price is likely to go up as things are found that need to be replaced. If you don't plan on putting a ton of new parts in the car during the rebuild, you probably need to set aside $4k.

I would skip on this FD unless it's got something you can't pass on i.e: pristine interior, perfect paint/body work, R1/R2, etc. Or if your plans were to rip the engine apart immediately...Just my $0.02

+1

i see it quite often when new owners bring their car in within weeks of buying it, now needing a new motor because the previous owner covered it up in one way or another.