I bought a 1990 300zx twin turbo less than 2 weeks ago. Car runs great except that it has been losing coolant. Replaced the radiator cap and thought the problem was fixed. Here's what is happening. Please let me know if you have any ideas as to what could be causing it.

When the car is cold, I check the coolant level and it's low. So I add coolant then crank the car with the radiator cap off to let the coolant circulate. While the car is still cold, the antifreeze bubbles out.

Any ideas?

 

Check the coolant level at the overflow bottle only. Coolant level in the radiator should always have a headspace on a cold engine because it will expand and overflow to the overflow bottle. So don't open the radiator. just add to the overflow bottle.

Ok so if the level is low a couple days later, wait until the engine is cool because you will need to inspect every joint. Start at the lower hose and rub your fingers where the hose clamps to the pipe and see if your fingers get wet. Be sure to run your fingers UNDER the joint as coolant travels to the bottom. If there is coolant leaking there, tighten the clamp and go to the next joint in the system. Don't forget to check bypasses, heater lines, seals at the t-stat housing, and other sensors connected to coolant too. When you check the last one at the radiator inlet, get out a flashlight and look for greenish or whitish scale around the water pump and at the crimps on the radiator. Sometimes the leak looks greasy or oily. Start with a cleaning.

Here's the thing. When coolant is hot you cannot find a wet spot. It vaporizes and leaves that stain as it dries up. You only find wet coolant when the car is cold. Second, the stain or scale IS the coolant leak. Anywhere you find the scale you should be taking a second look at whether the leak is right there where the scale is or if it traveled to that spot say from a spill or dripping from a leak above the stain. I've seen them run down a hose from a joint several inches away, drip down and collect on the splash pan. It could be challenging to find the actual leak. I would start by cleaning any coolant stains first then searching for the leak causing any new stains.

Can you smell it? Use the nose...
Pinholes will shoot out steam and you will smell coolant but not see the leak. They are tough because you wont find a stain at the leak but you'll see it on the spot the team is hitting. That's why I said to start at one end and check everything to the other end. You'll find it.

 

It hasn't leaked that I can tell since the radiator cap was replaced. Problem is that the radiator is dry and we can't get the fluid to circulate. So we're filling the car up with as much fluid as possible cold, but when we crank it, it's not circulating so that we can add more to it, so it keeps overheating. I've been told it could be a busted head gasket. Any other ideas about what it could be??

 

First you say you "circulate" when cold. That should'nt happen when cold. In the second post you say you "cant circulate". That's correct for a cold engine only. Change out the t-stat if it is stick open or stuck closed. Theyre cheep enough and it will eliminate the guessing.

Also I am confused by the words "low" and "dry" in your two posts . Use the overflow bottle level. If you deleted your overflow bottle we'll talk about that next time. Stop opening the radiator cap and going by that level. It should have air space at the top when cold.

While checking for leaks, clean up the sticky and scaley spots, Any smoke coming out the tailpipe? Any water in the engine oil? Losing any oil? Check the belts?, Radiator cap fully closed? The radiator commonly leaks out the tank crimp right on top. Or at any brazed fittings like the neck and overflow tube. Everyone is surprised when they finally admit that crud in that little channel around the radiator tank is really a leak. I can see why because it is always dry. It dries as it comes out, flashing to steam and evaporating only to leave a little stain and the odor of ethylene glycol. You must clean first. When you smell it, it's leaking. And it only smells when the car is hot.

Check the drain plug. LOOKING from above, you may miss the wet spots! You must look underneath or feel below the joints because of the gravity of the situation. Dry off any wet joints with a shop rag and see if they come back. I'll guess everyone who pulled a radiator noticed that whitish-bluish-greenish residue around the bottom edge of the core-to-tank joint. Thats a leak. Buy a UV flashlight and you will see more than you care to. You must use the yellow spectacles in the kit to get the best resolution. Assume any sticky green or greasey spot is your leak and then tighten the joints around it. Then use the UV light to look for other nasty things like refrigerant leaks or coolant in the oil. Then look for rodent stains around the garage or inside the car I let the kids play with Hi-Liters writting stuff on their hands. Then lit 'em up with my Uv - good times. Doctor says they get their vision back pretty quick.

 

Ok. We'll check all that. Thanks for your help!!

 

How fast are you losing coolant? If the other stuff doesn't turn anything up, check your heater core, especially if the cabin smells funny. I also had a leak above my overflow bottle that I fixed with some liquid gasket. I think it was sloshing around when I would drive and it leaked out that way. Yeah, not nearly as thorough or helpful as Turbopuppy but just a few more things to consider.

 

Thanks! We keep uncovering issues with this car. Right now we're changing the water pump, installing a thermostat (found that it didn't have one) and found a majorly worn out timing belt that we're replacing. It appears that the issue is no longer with losing coolant but rather with getting the coolant to circulate.

 

"we keep uncovering issues with this car"

Sounds like mine, haha. 6 months before I bought it, they took it to a shop and pretty much gave them a blank check. Fixed a ton of stuff. Told me to get a coolant flush because the shop didn't have the machine and think about replacing the wiring harness. Coolant leaked a few places, my heater core rusted out from under itself, the engine rpm changes when you wiggle the wiring harness. Oh, and the clutch just went (albeit because of my choices for leisure activities). Thing's a total nightmare but worth every penny

 

Im having the same issue as Speedy1. I bought my 1990 z32 n/a 6 weeks ago and i have a handful of issues with it but my radiator coolant leaks intermittently when its warm. I can smell it very well from the cabin as i drive but when i stop and it cools down the coolant will sometimes leak like crazy or it won't leak at all. Ive checked every single line as it was warm and cold and no evidence of coolant. Any ideas?

 

Yeah! I'm thinking my car is possessed!! Ha!

 

My car is doing the exact same thing you're describing. I'm sure it'll be worth the money once fixed but I don't think I can afford any more sudden issues. Now we're talking engine swap. Suggestions would be greatly appreciated.

 

You know how the thermostat isolates the radiator until the system warms up, right? If its leaking like crazy when cold, it suggests that the water pump isn't working much harder after the thermostat opens the system up and the larger system volume is causing less pressure in the system overall. Poorly sealed areas would stop leaking because of reduced pressure. Either that or if the pump speeds up significantly when the system opens, a higher pressure near the pump outlet is caused, which could cause a leak. I have no idea how great the speed changes are for a water pump when the system opens (if it even changes at all) but a good way to test it is take the car for a spin and drive it like you stole it. I know the pump works according to engine RPM so a higher RPM should cause more leakage. You can try this warm and cold to try and figure out which side is doing it too. This could explain why it only leaks some of the time because you only rev the engine up some of the time. Also, if it leaks all the time, that means the leak could still be but is probably not on the radiator side of the system.

Again, smell in the cabin screams heater core or nearby it but if it was "leaking like crazy into the cabin", you'd know it.

Sorry, no more solutions. Just a few thoughts. Hopefully it can help you figure things out.

 

Update lol water pump was the issue started it the other day and it started leaking fluid almost immediately so fixed that and everything is good again. Now i just need to fix the oil leak

 

I feel like a bit of an idiot now, telling you to check either side of the water pump. Good to hear you got it fixed

 

Glad you fixed the coolant issues. It might have been a smart idea to pressure check the system in the beginning, it would have showed you exactly where the leak was.