MaxxAction

Hi guys...

searched and searched and haven't seen these exact symptoms.

This is an Ls1 in a 300zx conversion I just recently finished. The motor is all new top to bottom.

I just swapped the stock thermostat to a 172 thermostat, and burped the system well, I think (I am going to attempt it again today and see if I get any more air out)

I am using c6 water pump for clearance, so I could use a puller fan setup (dual 12 inch, fully shoruded, combined 2600 cfm)

The radiator is brand new, top down aluminum mishmoto radiator with a core that is 22.75 wide, 17.5 tall, and 1.5 deep.

The lower radiator hose is long, made of two chevy truck hoses because I had to run it under the oil pan and back to the radiator, no spings in the hose.

All of the undercarriage air guides are on, intact, and solid (stainless plate)

The temperature recordings are all off of the megasquirt software on my laptop.

Here is the issue. When I am just out cruising around the hilly back roads of eastern tennessee, ( 40-50 mph 3rd-4th gear 3000 rpm, moderate load), it will climb up to about 225. If I pull over and let it idle, it will drop right down below 190.

On the interstate, at 75mph, (3k rpm) it will run between 192-194.

If I romp 1st through third shifting at 6500, the temp will jump up quickly to 225, and if I just cruise slowly, it struggles to bring itself back down

I can start the car, let it idle for an hour, (which I did last night while tuning the idle) it will idle at about 188-190 no problem. I have the fans set to come on at 190. It will climb to about 193-195, then the fans pull it down below 190, and kick off.

So the question I have is why would it idle cooler than it runs on the interstate?

With the VG motor that was originally in the car, it was the exact opposite. Idling temps would reach 190-192, but as soon as I got the car moving, it would drop to 180, and if I would hit the interstate, it would run down around 172 (thermostat temp).

Some pics of the setup:



Radiator/fan



lower hose/modified thermostat housing

Here are my thoughts, either

A: I have air in the system,

or

B: my lower radiator hose is sucking flat.

Anyone else seen this or anything similar?

MaxxAction

For anyone interested...

I burped the cooling system again. When the thermostat opened, I squeezed both heater hoses about 20 times running down the length of them from back to front, and got several big bubbles to work out of the system. After that, I let it run with the funnel in the radiator and got a little more air out as well.

I used a cork to plug the funnel, let it cool down til the coolant had receded into the radiator again, and too it for a drive.

Never got above 202 slow cruising around the back roads where it was getting over 220 before. Idle temps are the same, and interstate temps were a bit more variable. On level roads, low load, it would drop down to 192-193. When I would hit a long stretch of hill, it would climb to about 200-201.

I did pick up about 20 degrees where it was causing trouble before purging it again, but those interstate temps still seem a bit high to me with a 172 thermostat.

LLLosingit

iTrader: (4)

Your cooling system doesn't know that it has a 172* thermostat after the temperature is above 172 degrees it's open the same as if you had a 190* thermostat and the water temp was over 190* it would be open also. Your thermostat is there to make sure your water temp isn't to low.... Not to make it run cooler.

LLLosingit

iTrader: (4)

Is that a single double or triple core radiator? 200* isn't a problem by the way.

CAMSTER

iTrader: (10)

Did not read whole story think socking hose flat at higher rpm trick is aluminum tubing with small connector hoses on engine to rad side (vacuum area) If problem persist repeat in return side as well.

What you are experiencing is common to long rubber hoses.

When not made for particular purpose is end result, reason why longer hoses are often triple price.

Good luck, hope this helps.

99Bluz28

iTrader: (35)

Your current coolant temperatures after your latest update sound perfectly fine, you're good-to-go!

MaxxAction

Thanks for the replies...

I am still trying to wrap my head around 220 being ok. The VG motor that was in it, 220 was getting into the territory of potentially warping heads.

MaxxAction

Single.

LLLosingit

iTrader: (4)

210* common on late model engines, Good for emissions but not performance. So while 220* is hot it's still below the point where damage is likely to occur.
I looked at the Mishmoto website and the radiator they list for a1990-1996 300ZX twin turbo is considerably larger than yours and it a 2 core 27.2" x 20.2" x 2.55"

Kiwi_Camaro_2010

Silly question maybe, your fans are definitely pulling air not pushing? that may give you your situation so at idle air is freely moving forwards when car not moving, but when moving, air trying to go in both directions through radiator, just a thought.

MaxxAction

Yes...

that is about 1/4 bigger than stock. The stock TT radiator was thin, like an inch thick.

The guy that designed the swap kit I used is using the same radiator I am on a 6.0l motor in his vert Z with no issues.

I can't fit any thicker radiator in my setup. If it becomes an issue, I have thought about running a second small radiator in series in front of this one.

MaxxAction

Yes...

they are pulling in the right direction. These fans are good for 2500 CFM. I think the stock fans on most Ls powered cars are pull like 4k CFM, so I may be a bit short on fan. I have room to add an additional fan outside the AC condesner, in fact I could reinstall the Ac condenser fan and pick up another 1100 cfm or so from it.

my406cid

Was this car ever equipped with some sort of lower valence or skirt on the lower core support? If iirc the rad needs a scope to create a low pressure area behind rad to pull air thru. 4 an into this one on a third gen comaro.