This is a bit of a double post so I apologize -- just trying to isolate this issue.

I recently installed a new rebuild and had some trouble initially getting it started. It now starts but is behaving, from what I can tell, as if it has a coolant seal leak.

On the very first drive, the coolant overflow tank line snagged on a belt and pulled out of the nipple on the overflow tank. The car subsequently lost about 3 liters of coolant and overheated to about 125C.

Given that the overheating happened on the maiden voyage, it is not clear if the symptoms I am seeing now are the result of the overheating, or of something else:

1. Car starts fine cold
2. Car starts fine hot
3. Car struggles to start when "warm" (about 20+ minutes after shutting down)
3a. 10% throttle will often start it
3b. A squirt of starting fluid will start it
3c. Idle is low and erratic/lumpy for 5-15 seconds after starting when warm
4. Good compression when cold, not tested hot
5. No white smoke, but some blue smoke on cold startup
6. Coolant does not appear to be disappearing, although I've only put about 150 miles on the new engine
7. After the most recent drive, I parked it, went inside, came back 10 minutes later, and coolant was spilling onto the ground from the overflow tank.

Debating whether I should bother with a cooling system pressure test or just call it and start pulling the motor out.

 

A brand new motor with that minor amount of overheat for a limited time and I doubt you have a coolant seal failure. I would look at the external parts of the system, though - make sure that line to the overflow is 100%, fill the system with the Lisle funnel, good radiator cap, good thermostat.

New motors can sometimes be a bitch to start warm. It's also possible your tune or injectors have something up with them, I know you had those stuck injectors in there for a while.

Dale

 

I will check the overflow line. I did fill the system with a Lisle funnel and let it idle for about 20 minutes (filled with TB coolant line disconnected until it started spilling out, then connected it and continued filling). Radiator cap is about 18 months old... Thermostat is new OEM but I know sometimes those can be problematic so perhaps I will replace that.

As you mention, injectors are brand new (OEM primaries & Bosch 2200 secondaries). The problem persists all the same with OEM ECU installed.

What could cause the overflow tank to spill out like that after the car is shut down? I never understood that. A stuck thermostat?

 

Most times it's a pinhole in the line from the radiator cap neck to the overflow tank. As the coolant warms up in the engine, it expands and the excess goes into the overflow tank. As it cools, the excess is sucked back in. If you have a pinhole in that line, the system sucks air in and the coolant stays in the tank. A few drive cycles and you've shoved a ton of coolant into the overflow tank and it barfs it up.

That line has to be rock solid. 6mm silicone vacuum line does fine FYI. Also a bad radiator cap can do something similar.

Dale

 

No idea if a "radiator cap" is AST or filler neck or deleted AST. I've had one fail in a seldomly used FD in a short time period.

Thermostat is an easy test and you'd be foolish to discard to swap in another for a hail mary.

Pressure test kits, or maybe a tee-kay, if you're afraid to drive the car, aren't hugely expensive and might deliver peace of mind. I'd certainly try that first before pulling the engine and potentially having to spend another $500+ on gaskets and seals that are potentially fine.

Your fill method is how I get rid of the low spot at the back of the engine, so that should be good, if the rad isn't in a weird and wonderful position and the hoses are solid to the squeeze, I think the bleed should be good.

 

Will definitely check and replace that.

AST delete -- the car did sit for ~6 months without use. Will try replacing that, too...

What is a tee-kay?

Radiator is in standard position and hoses are OEM ~2 years old, seem fine to me. I did find that mice had stashed acorns in the hoses while the motor was out... flushed it out real good with a hose then distilled water.

 

I'm betting the overflow after shutdown is a bad radiator cap or a bad seat (corroded, etc.) for the radiator cap seal. Engine hot spots will cause coolant pressure to build after shutdown, and if either of the above are bad it'll spew coolant.

 

I actually noticed that coolant temp, as read via OEM sensor/PFC, will rise from about 87-89C at idle to as much as 105C after the engine is shut down.

 

My car (stock, 16k miles) recently started puking coolant from the overflow after shutting down as well. Curious to see where this goes.

 

Why do you imagine that is?

I did read another thread where somebody had very similar symptoms to me (minus the coolant escaping the overflow tank) and they said it just went away eventually...

 

New motors are still breaking in and building compression. Rotary engines have less compression when hot by nature, and a motor that is still building compression can be a bit tricky to start when hot.

@c0rbin9 you need to do a test to see if you are getting combustion in the coolant, it's well documented on the forum. That's the bad thing with cars that sit, the coolant turns corrosive if you don't change it regularly and it can either corrode out the walls around the coolant seals leading to a failure or the seal itself goes. But, do the same troubleshooting I've already covered in this thread. Also the coolant overflow tank has a dip stick with a Full mark - that is the MAX you want. If you fill it over that it will puke out even with a healthy system. Remember, the system naturally pushes coolant into the overflow and pulls it back as the car cools. If you have too much to start with in the overflow tank it has nowhere to go but the ground.

Coolant temp when the car is off doesn't mean anything. The cooling system isn't moving and it will heat soak. Temps should come down almost immediately after startup with the water pump cycling it through the system again.

Another good question is do you have the stock AST or is it eliminated. If so how is all that plumbed in. I would take pictures and post. I've seen people get REALLY confused with doing an AST delete or even hooking up an AST in general.

Dale

 

A second what @DaleClark is saying... we need to see your AST setup. If you've deleted it, your system has a single radiator cap. Might be worth checking / replacing the cap with a proper one. The factory "cap" isn't pressurized/sprung. The pressurized/sprung cap is on the AST. Obviously, you can tell if the cap has a spring / pressure rating on it. Make sure your single radiator cap on a deleted AST is pressurized type. If you still have your AST, the AST should receive the pressurized cap and the filler neck should have a non-pressurized cap. Running two pressurized caps will cause coolant to go haywire and overflow the tank. You'll get substantial coolant loss. Running a AST delete without a pressurized cap, you'll get the same.

 

My AST delete looks like this:

• 93 thermostat housing
• Banzai billet aluminum filler neck
• 93 thermostat housing cap (no spring / KF01-15-205)
• Rubber hose from nipple on Banzai filler neck to overflow tank

I ran this setup before the rebuild, and never had coolant spilling out the overflow tank after shutoff, but did have coolant disappearing between drives.

 

You need the sprung cap. You're not pressurizing your coolant system.

 

So without the spring cap, does that mean any coolant expansion whatsoever goes into the overflow tank? And then, so long as the tank doesn't overflow, it gets sucked back in after shutdown? Whereas if you had, say, a 16psi spring cap it would only overflow after the system becomes sufficiently hot? Under what circumstances would the system become hot enough to start overflowing into the tank? A normal drive? Or something more substantial?

Can I put the OEM AST cap onto the filler neck?

 

Yep, that's your problem. You have to run a spring cap there.

The spring cap puts the system under pressure as it warms up. The cap is rated at, say, 14psi - that means the cooling system will be at that pressure. This also increases the boiling point of coolant. Remember, coolant boils at 100 deg. C/212 deg. F. With it under pressure it's much higher than that. Also without it under pressure you can have localized boiling.

So, yeah, just get the spring cap from your AST, install, and you are good.

Dale

 

Something like, hoover = a vacuum. It just a test for combustion products in the coolant, probably a different name over there?

You've got a simple fix at least. Just in case, I'd be making sure your coolant sensor is good and the buzzer is working in the car based on running around unaware of this issue previously.