Air in Cooling System

Recently purchased a 300 TT. 111,000k's and counting.

Let me say right up front - I know very little about these engines, but enough about engines in general.

This issue has just begun; I'm getting a constant flow of air into my cooling system. Mechanic says it's not from a cylinder (blown head gasket) since his "tests" show there is no combustion fumes in it. Have replaced the radiator, it was leaking anyway. As far as we know, there is no water "escaping" from the system.

So here's a few querky points about this issue:

When pressure tested - it doesn't rise OR fall :s Pumped the little test thingy up to 25 (psi?) and it didn't move while engine was running, or not running. This would sugget that there are no leaks into or out of the cooling system.

However, when radiator cap is off, I get a constant stream of tiny bubbes, not in a terrible hurry, forming at the fill. Sticking my finger in there reveals that they are quite hot, which would suggest they are coming from somewhere even hotter

Have parked her on a hill with the heater full crank to be sure to cycle water through there as well. Same stream of bubbles, no sudden increase or drop as the heater valves open. Heat inside was as expected, not too low; ie: heater is working.

When I drive her normally - well, the way she should be driven she gets about 20k's before I lose enough water to cause the temperature to rise and thus steam is produced and I lose water completely and have to stop.

My suspicions are - Turbos. But this is where I need some knowledgable people to correct me or confirm... Since the manual tells me that these Turbos are water cooled, this would suggest there is a gasket between the engine block and the Turbos allowing water to circulate around them. IF there was a crack in a Turbo, or a gasket related to the mounting of the Turbos - would this be the cause of my constant stream of hot bubbles?

My reasoning for this suspicion: I am running stock Turbos, and from what I am told these are set to about 7psi. So this would naturally balance out when the radiator is running as per normal, and perhaps a tiny amount of water gets into the "leaky" Turbo, but get's vapourised - hence no real noticable performance issue. However, if I put the foot down regularly the Turbo pushes back and fills the radiator with air, eventually emptying it and abra-cadabra I have my problem!

Please, if anyone can confirm that they have dealt with this problem before, and maybe correct me on anything I have suggested here, that would be WONDERFUL! I really want to drive my Z the way it BEGS to be driven WITHOUT being paraniod about craking something terribly expensive! :s

Thank you.

Pete.

 

Check the water pump, block pressure should be around 10psi with the t/stat open, rad cap on and engine running. Bubbles are likely to be cavitation from a stuffed water pump impellor.

 

Welcome to the forum, i hope someone can help, you certainly have provided plenty of information.

Great first post.

PS The manual says MAX 14 PSI on cooling system pressure test or damage could result.

 

Thank you for the welcome Brisz

We are aware of the running pressure. Just wanted to give it a reason to fail
But of course it holds :s

Thank you drz400y. I will check that out. Bit of a mission, but was looking to replace the fan soon anyways. Guess now is the time

Will come back with results asap.

Thank you gentlemen.

 

I gather you're asking if it's possible for the pressurised air in the turbos to get forced into the cooling system ?

Never heard of that happening, I understand that the water jacketing for the turbos is completely divorced from the gas flow side of things.
No interface between the 2 in the form of seals, gaskets etc.

Good first post by the way, you gave plenty of useful data to start with.

And welcome to Hell.

 

Thank you Mick. I guess I've been doing computers and forums longer than I've been doing Z's But I'm sure you'll see more of me here now that I own one... *cough* I mean, now that my BANK owns one :s

Cheers guys. Appreciate the warm welcome. I'll get to work on her and get back to you all, hopefully with some good news.

Is it just me, or is it warm in..... OMG!! Hi Lucifer! :s

 

Hey guys. Can someone show me, hopefully by way of Photograph, where to find the heater system bleed valve? I may be wrong, but I read somewhere that on the hose line that takes water from the engine to the heater, there is a bleed valve. And that this is possibly the highest point in the water system, thus a good spot to bleed air from.

Can anyone confirm that this is true? And hopefuly point me to it. These bloody engines are so BIG, it's hard to find anything on 'sight' alone. I find myself performing world class acrobatics just to get my hand up inside the engine bay to find a pipe... and then my hand takes up all the free space between the car and the motor - hence I can't SEE what it is I'm touching!! Talk about frustrating!

PS. FOR SALE - '89 300ZX VGDETT Z32 with 111,000k's and a mysterious small air leak into the cooling system!!

 

Nope, no such valve. It's just a hose in and a hose out that connects directly to the block.

The only air valve type things I know of is on top of the radiator on the drivers side.

I'll give you $2k for the Zed

 

Sounds like your loving it. :zlove:

 

Thanks Chrispy, but your offer is far too generous

 

Thank you everyone for your contribution!

Hey guys,

Has been 2 or 3 weeks now and I haven't had an over-heating problem. As I continued to baby the problem and look for a cause it just became less and less of a problem. Have not had to "top-up" the radiator for a couple of weeks.

Seems there must have been a heck of a lot of air through the entire system! Who knows...? :s

She's cruising along now without any over-heating. Mostly sits just below half way. Did get up to the top just the other night when I was parked on a slope and left her running for 5 minutes after a highway run, but that's to be expected, and it went back to normal once I took off again. I suspect it's just a little bit of air still in there. I'll top up again, and that should be the end of it.

So for anyone else who experiences a cracked radiator, hose etc. Just be prepared for this kind of recovery. It takes 2 weeks to get all the air out of this monster!! :s

All the best guys!

Pete.

 

but off topic, has the 100k service been done?

 

Valid question. Only purchased her @ 109k. So, I'll look it up and get back to you.

Meanwhile - Why do you ask?

Could I be missing something?

Cheers.

Pete.

 

cos if that hasnt been done it should be done asap... many problems can be found and solved just by doing that service, which includes the waterpump & thermostat which could be a part of the problem you experienced