First Generation Z Car - Cooling Systems

by Dick Denno IZCC#452

I have received several inputs to my cooling solution note and I need to give the Z-community some more background to help understand the bigger picture. My car is a '72 240z restored about 6 years ago to factory specs. It was as accurate as I could tell, reconstructed to look just like it did when it left the factory, down to the original steel wheels and hub caps. When I started driving it it was as close to a new car as I could make it except for the dealer installed ARA air conditioning and a 4-row radiator. I did install the fan shroud and belly pan which did not come with the car when I bought it. Remember, this car also has an automatic transmission and operates in S. California. My surprise was that the car ran hot and often vapor locked. How could Datsun have marketed a car in the early 70's with that kind of performance problem? I began a long quest to identify and correct a number of problems, some of which I have picked up on from IZCC and some from my Group Z members. In my opinion, the early Datsun Z-car has 4 cooling problem areas. These are:

  1. Bernoulli effects or air flow reversal through the radiator.
  2. Vapor locking - fuel vapor pressure related.
  3. Inadequate under hood circulation - high temps.
  4. Inadequate fan air flow through the radiator.

All of these problems relate but we have to talk about them independently and discuss how each is to be corrected. The changes I have made over the past six years are as follows:

A. Replaced the stock 15" fan and clutch to address problem #4. This was an unnecessary fix because my original fan and clutch were OK.

B. Many times removed and replaced the fan shroud, belly pan and lower front end sheet metal to address problems #1 and #4. Part of these experiments involved the temporary addition of an air dam. The air dam worked but it destroyed the original appearance of the car so I removed it.

C. Cut the metal brackets supporting the metal fuel lines to the SU's and bridged the gap with a non conductive material. Also insulated the fuel lines with a silicone tubing. These mods are still on the car but in my opinion, not effective in addressing problem #2.

D. Replaced the original reciprocating York air conditioning compressor with a Sanden rotary and cut a window in the original ARA compressor bracket. These mods addressed problem #4 and hopefully #3 by reducing the amount of fan airflow blockage, the rotary compressor has a smaller pulley and cross section, and allowing air to flow through the ARA bracket. I still have this mod. The rotary compressor does a much better air conditioning job and it is quieter but I cannot say that it fixed any of the above 4 problems.

E. Added a 14" Scott electric fan with two circuits to turn on whenever a high radiator temp is sensed or whenever the air-conditioning compressor is on. This mod is still on the car because it seems to keep the head pressure down on the air-conditioning system and it does help keep the car from vapor locking. I had an experience last summer when the fuse in the electric fan circuit failed during a hot slow drive and the car started to vapor lock.

F. Added early 280 hood vents to fix problem #3. There is no question but this does reduce underhood temps. I can tell via the soles of my shoes. The floor boards are very cool now. I think this fix also helped with problem #2 because the left side vent is located over the SU's.

G. Added a 280 16" Fan to correct problem #4. I am sure this easy fix is working. It will also help address the other 3 problems.

Another indirect change I made was to replace the original distributor with an HEI version from a 79 280ZX. I was experiencing a thermal lockup of the advance mechanism in the original distributor which the 280 version does not do.

As a result of my last posting, Jim Brumbaugh identified another problem he has fixed in Orlando. He believes there is a strong thermal coupling between the exhaust manifold/baffle and the air filter box. I agree but we cannot remove or modify the stock air filter in California. Jim simply replaced his with Victoria British Longflow units. I am going to try painting the exhaust baffle with a white high temperature paint and possibly the lower segment of the air cleaner box also.

I hope this more lengthy explanation will help any further discussions. If you live in the cooler climates, many of these fixes are unnecessary. I do believe that the addition of the 16" fan is the best all around fix and it will address all 4 problems at minimum cost.

Best Regards,

Dick Denno

In his Second Post - Dick added:
I would like to add a 5th area of concern to the original list of 4 cooling prolem areas:

1. Bernoulli effects
2. Vapor locking
3. High under hood temps
4. Air flow through the radiator
5. The new area - Radiation from the exhaust manifold

These areas probably interrelate but we need to separate them for discussion purposes. I have been conducting various tests to understand a power loss behavior of my 72 240Z.

When I start off, especially in the morning, the car has plenty of power. After about 10 15 minutes of driving there is a loss of power. I have observed that the loss is a function of the temperature gauge. A higher temperature meant a lower power level. What I found was that the air induction system was heating up, with time, preheating the air intake to the SU's. If, after about 30 min. of driving, I stopped the car and checked the temperature of the air filter housing, I found it almost too hot to touch. The hot spots were low, in the center of the housing toward the SU's and forward on the inlet nozzle, facing the distributor. I isolated the air filter housing by placing non-conductive silicon sponge gaskets between the SU's and the housing and also placing non-conductive washers on the brass attaching fittings. I also placed a small aluminum baffle between the air filter housing and the carburetor pre-heat nozzle projecting out from the exhaust manifold. The results of this test were very encouraging. The air filter housing stays reasonably cool, except for the part that is attached to the SU's.

I made another trip to the junkyard to try and understand what Nissan did to address the apparent exhaust manifold problem on later models than my 72. I found the following changes:

1973 240Z had a larger exhaust manifold heat shield baffle, smaller carburetor heat nozzle and all fuel lines insulated.

1974 260 Z had the same larger exhaust manifold heat shield baffle that the 73 had, insulated fuel lines, smaller carburetor heat nozzle and a 16" radiator fan. I also noted that Nissan revised the exhaust system to locate the exhaust manifold outlet so that it is centrally located and the Y fitting that is located low, under the driver on the earlier Z's, was moved up near the exhaust manifold.

I believe these changes were made to reduce the radiation views between the exhaust system and the air induction system. There is just too much heat being radiated into the air inlet filter housing and possibly the SU's also.

If you live in a cool climate, have aftermarket air filters or exhaust headers, this may not be of any concern to you. If you have a stock configuration 70-72Z, some change is necessary to bring the induction system temperatures down. It looks like some kind of exhaust manifold baffle improvement is called for. I will let you know if I find a simple solution. I have a 73 Baffle and I may try it.


Dick Denno