Background: I have a '94 Q45 with 138,000 miles. I have owned it for 10 years having bought it from my neighbor who was the original owner (83,000 miles at time of my purchase). I have all service records on the car. Water pump and thermostat replaced by original owner. I replaced plastic fan blade and fan clutch several years ago. Fan clutch still operates properly. Electric pusher fan operates when A/C is on and when temp rises above midpoint on gauge. Recently done the Plenum job including Nissan brand knock sensors. I filled the cooling system with distilled water only, to check for leaks. Car starts right up, runs smoothly and temp rises to and remains at mid point on the temp gauge while idling. It would seem that all is well.

Now the problem: After about 5-10 miles of any type of driving the temp climbs to the point that the needle is about to max out. I immediately pulled over and popped the hood. I noticed that the plastic side tank on the radiator was pissing steam apparently due to a crack below the upper hose nipple. I replaced the radiator with a new one and refilled with distilled water only. I pulled the car up onto ramps and burped the system three times by removing the cap on the radiator itself and monitoring the exodus of bubbles with several blips of the throttle to accelerate flow through the radiator. After three burping cycles I took the car to the local smog guy for its bi-annual smog check and the car passed with no difficulties. However, during the smog test the coolant temp rose considerably with coolant seeping out of the radiator cap above the thermostat flange. After cooling off I drove home (about 3 miles). By the time I got home the temp needle was within 1/4" of leaving the operating range. Stopped the car, allowed it to cool off and checked coolant level. Coolant level in the radiator was still at the notch about 1" below the filler neck. No evidence of coolant loss or steam. More burping cycles, a new radiator cap and another test drive around the neighborhood. Temp still climbing after a few miles.

First question: is the proper radiator fill level the notch about 1" below the filler neck on the radiator? If not, what is it?

Second question, is the use of 100% distilled water during this test run part of the problem?

Third question: Am I doing the burping correctly? If not, what should I be doing differently?

Anything else I am missing here?

Thanks in advance for any suggestions that lead to a "normal" temp during operation.

you want this:
http://www.tooltopia.com/lisle-24680.as ... 7AodEG4A5w

pick a supplier of choice, the keyword is Lisle24680.
put this on the UPPER filler neck (not the radiator).
Yes, ideal is 40% OAT (make sure you get all the green crap out first), 60% distilled H2O, and 12 oz redline water wetter as you wish.
what radiator did you source? a lot of the cheap chinese crap does not meet oem specs (tube density, etc).

What type of radiator cap did you purchase? I only use Nissan caps. Also, the Q has two radiator caps: one on the radiator and the other on the pipe above the water pump. If I remember correctly, I did the burping and filling from the cap on the pipe above the water pump with the Lisle Kit. The 90-96 model Qs are not hard to remove bubbles as I recall. Distilled water is a good flush. After I flush out mine I use Zerex G05 with Red Line water wetter.

First off its great to see another Bay Area first generation owner, they seem to be few and far between theses days.

Usually a system like this doesn't need to be bleed like that unless your coming from a completely dry system. The overflow tank near the battery should take care of any air in the system, but if the line or ports to the tank are clogged or partially clogged then it wont work properly. Also make sure you open the heater core completely by following the procedure in the FSM if you didnt.

To me if your not loosing coolant then you have a clog somewhere. I would replace the thermostat with a nissan unit, did the original owner say if they used OEM or was it done at a dealer? Its not impossible that it has failed even if it was oem.

JeffTepper wrote: Second question, is the use of 100% distilled water during this test run part of the problem?

Yep.



Pure water boils at roughly 15 degrees less than a 50/50 mix of water and antifreeze.

Definitely use the cap on the filler neck instead of the radiator. The Q is pretty easy to burp... I just top it off a few times after a flush and it's good to go until next time unless something leaks.

Heath

There is absolutely nothing wrong with running pure water in a cooling system, that is not the problem. The graph you showed skibane is at atmospheric pressure which the cooling system is not at, it is under pressure. This raises the boiling point of the water considerably, way beyond safe operating temperatures. The only problem is that it evaporates, so you will have replace water regularly and there are no corrosion inhibitors. In fact distilled water should help the problem since it has a specific heat then antifreeze+water(1.005 vs 0.865 respectively).

The boiling point at 13psi above atmospheric of pure water is 242degrees, even at 6 psi its 228. Plus many of the race cars and drag cars have to run pure water because of regulations and performance, but they never seem to have a problem.

So if your system is not holding the correct pressure of ~13psi, the the water may be a problem but otherwise it wont be.

Thanks for the suggestions. I plan to locate the Lisle kit today and will post results once I have completed the next round of burping.