cant keep coolant temps in line

[sbz0kgx]

So I've been slowly trying to track down the source to my cooling problems. Started after the engine rebuild "6 bolt swap", the car wouldn't go over 200 degrees at idle with the fans always on, coolant topped off with about 50% in the reservoir. I had a new gates water pump, new oem t stat and cap at that point. I could drive it slowly and within 15 mins the temps would shoot up to 234. Highway speeds were more or less the same result. I proceeded to install some ducting between the FMIC and the condenser with little improvement. My latest setup is a mishimoto X line aluminum radiator, no t stat, stock fans always on. At idle I see between 174 and 180, cruise is about the same, if I get into boost the temps stay between 200-205, but when I stop or idle they climb uncontrollably. If I hold the throttle to 3000 Rpms for a few seconds, temp drops to 200 then quickly starts to climb to the 230 degree range again. If I drove again after the pull, temps seem to stay in check but shoots back up at idle. I have performed a leak down test with no negative results, flushed the system several times and bleeding the air out, I'm leaning towards a head gasket issue. What are your thoughts? Am I missing something?

 

[gdb1039]

If it's a head gasket issue your would be either burning water our mixing water in your oil. Are your coolant levels dropping at all?

 

[sbz0kgx]

coolant levels drop after a drive, pushing into the reservoir, if I crack the radiator cap, air comes out with no coolant to be seen.

 

[Diamondstartech]

By leak down you mean pressure tested? If so how long did you let the system sit pressurized? Sounds like a head gasket. What's you're fan set up I looked at your profile but no details in that respect. During a cold start is the exhaust white? Do you have access to shop air with a blow gun? If so I can tell you a little trick to possibly pinpoint the leak

 

[sbz0kgx]

The leak down test I performed was to hook up the air compressor to the cylinders via a cylinder compression tester, each cylinder held pressure but only tested for about a min or so with the rad cap off looking for bubbles. Fans are stock. Exhaust is not white at start up or any other time. And yes I do have access to an blow gun.

 

[Diamondstartech]

I'd start by pressure testing the coolant system if you haven't already. Let it sit for at least an hour. Was the 6 bolt head and block machined prior to the head gasket install and we're they both checked for being flat? You can take a spark plug out put that piston at bdc and blow compressed air in the hole and if you see bubbles bingo.

 

[sbz0kgx]

Yes the block and head were both machined, block was decked to accommodate MLS head gasket and head was resurfaced. Ill pressure test the coolant system as soon as I can. I didn't see any air bubbles when I did the leak down test but I will for sure try your trick

 

[Diamondstartech]

Those mls gaskets are very unforgiving if your head and deck aren't even and flat sorry but head gasket is the culprit I believe.

 

[ceedawg]

You purged all the air out of the coolant system I will assume. And you are certain your fans are running at idle?

I have a similar issue to you and I'm 100% sure it's not my head gasket. Don't keep letting the temp shoot to 230degrees you will blow the headgasket. At worst put your heat on full blast!!! Windows down of course.

Make sure the fans are spinning in their proper directions as well. I think you have excess air in your system. I would recheck those issues before I'd go pulling off the head.

I will be doing ducting and a hood vent. I will also be putting twin 350z inlet ducts in my front bumper. My cooling issue is due to my huge fmic not allowing efficient cool air during idle to cool down the radiator.

 

[sbz0kgx]

I have purged the air out of the system countless times with heater on full blast, following the instructions in the service manual, as well as other tips and tricks I've learned from research on this site. I usually never let the temps get into the 230s however this time I wanted to see if it would drop at some point, wishful thinking I guess. I have OEM fans functioning perfectly. The last time I purged the system of air, I spent quite a bit of time massaging the lower and upper hoses in an attempt to purge air. After I ran the engine with the heater on full blast, waited for it to cool down, and topped the coolant off, I was sure I got it all out. Took it for a drive and temps stayed at 173-180, got into boost a few times with the temps reaching a max of 203 with the heater on. When I returned home I idled it for about a minute and watched the temps rise to 223 where I stopped it. I can hear a hissing/bubbling sound coming from the timing side of the motor, near the water pump. Im sure my leak is on #1 cylinder. I checked the coolant and sure enough nothing but pressurized air came out. The new motor doesn't even have 50 miles on it, all parts have been replaced with the exception of the fans and lower rad hose. ceedawg thanks for you input, I will definitely spend so more time trying to purge air before I yank this engine out. I dont think it will be an easy job trying to time a 6 bolt in a 2g since the tools dont work with the swap. Good luck with the 350z inlet ducts

 

[miguelmcv]

What fans do you have, have you check a leak on the cooling system and/or a bad radiator cap will drain your coolant system and will leave the reservoir full of coolant.