keeping a jeep CJ cool with a 401

6/10/2010 update

People talk about it, people allude to it but no one ever seems to post the specifics. heres what has worked for me in pretty hot central valley CA temps 100+ in the summer

this combo keeps a warmed 401 reasonably cool in the summer.


Engine fan:
For engine fans that fit the stock shroud and suck lots of air.

1. early 1970s - late 1970s Cadillac eldorado and others running 472s and 500's came with an 18" 3-1/4" high pitch 7 blade fan
2. also there is the 1981-1986 Cadillac with the 4.1L v8 it is 7 blade an 18 inches also with similar pitch right at 3" -3-1/8" and moves a lot of air. It is unique in that it as a reverse bend on the top of the blades easy to spot

I picked up one of each for $5 a piece from pick and pull so $10 total they both seem to pull the same amount of air. pretty incredible difference.

Fan Clutch:
For the fan clutch I used a Hayden Severe duty fan clutch #2797 (buick with the diesel in the early 80's on some models like napa i had to notch the holes just a smidge to clear the bolts into the water pump but on a summit model i didn't, it was slotted deeper with universal slots). $48.79 from my local napa

For Shroud:
Stock CJ7 V8 shroud (stock no cost) if you go with a v8 replacement radiator. If you use the larger core http://www.cgj.com/shop/radiators/an.../jeep/jp-3006/ JP3006 the factory 82-86 HD w/ AC 6 cyl fan shroud does work and it accomodates a 18" fan (there were 2 styles of 6cyl fan shroud) but i recommned you build one if you want the bigger radiator. its cleaner and you can center things up better via moving the radiator up and down to get a good fit


For Radiator:
For a bolt in radiator i so far have found a couple of options for bolt in at a decent price with a stock shroud.
but remember the surface area of a V8 radiator is only 372 cubic inches (15.5"x24") +/-, the shroud can't accomodate anymore. other options are cross flow and they require a different shroud and radiator hoses which is fine but i didnt want to spend bookou bucks and change too much at once plus the other thing that irked me was that the side tanks cut down on the amount of core surface area you can capitalize on by quite a bit and the way a jeep radiator support is down flow maximizes usable surface area without lots of cutting

For cheap:
for aluminium down flow design radiators they are out there, they are not overly cheap but they are pretty close price wise to a high efficiency brass radiator these days. The big thing is they are bolt in and thats the key, usually fit and cooled better than the extreme 4 core radiator i got from extreme radiators a few years ago. the one i had was 3 rows of 5/8" cores and with a stock shroud it got the job done alright but the surface area wasnt there in the core for the cubes of my 401 on long hot days, im convinced now that surface area dimensions are key to keeping a crawler cool as well as efficiency. I suspect i used to heat soak it at low rpms (i know an electric fan would help here but i hate getting away from a mechanical fan on a crawler) and take awhile to cool back down. On this oldradiator, the number of tubes and the fin count was less than the brice thomas radiator but bang for your buck as a option its a good deal, i used mine only over the summer and decided i wanted to bite the bullet and go bigger on my cooling system. So i opted to finally bite the bullet and get a BTR , they also make a bolt in v-8 cj radiator. it is a great high quality bolt in unit, uses your stock shroud is very efficient and can be ordered with larger tubes.....the only catch its still a little small on core surface area at least the way im seeing things. So i took the harder way .......



To really get the most core suface area and cooling:
If you have the know how to stamp out a 3/4" deep rectangular tray, cut a round hole and make your own fan shroud.... it takes an afternoon and is well worth it then the better option is the 6 cyl radiator with more surface area than a cj V8 radiator (408 cubes (6cyl) vs 372 cubes (v8 15.5"x24" )) and 81-86 radiator support/grille (the late model grille is deeper than the 76-80 and allows for 3" thick tanks over 2.5" tanks = the option of a thicker core) these guys at brice thomas make jeep radiators that are down flow and they'll do custom work for reasonable. I ordered the JP3006, the core is 17"x24", i had them modify it to run dual 1.25" tubes vs their configuration of dual 1" for a minimal charge you might even be able to do slightly thicker by 1mm or two. the tanks ended up 3" thick fit flush which into the late model CJ radiator support meant no issues or changes in the fan to core clearance from my old 1976-80 raditor support and stock style V-8 radiator. my advice is Do not let them tig on the brackets, make your own, also have them notch the lower tank 1" x 5" wide on the driver side to give you more PS line clearance (highly recommended), you'll need to move it up or down and set the depth yourself, nobody ever sends a raditor with the brackets set perfectly and with tanks this thick you need every 1/4" worth of proper clearance make it count ask them to send the brackets seperate if you know someone with a tig welded its even better.
http://www.cgj.com/shop/radiators/an.../jeep/jp-3006/

I wish they would make the lower tank with the notching and sell this radiator as a V8 option because it really does work much better than anything else ive tried and ive tried alot to keep my bored and cam'd 401 cool

All said and done its a little more money but a whole lot more radiator and cooling. Lets just say im more worried about an exhaust leak these days even on a 105 degree day i havent seen much over 180-185 degrees out of my jeep. Novak wants $400+ for their setup and i can tell you that this has more surfae area in the core and more capacity and is imho a better fit than their setup when it comes to running an amc 401 under the hood



For a thermostat:
Combined with a 180 mr gasket or robert shaw high flow thermostat $14.21

For coolant:
I run 30% dextron synthetic coolant and 70% Distilled water with 1 bottle of water wetter $32.87

Water pump:
Flow cooler water pump $89.95 (i already had one since my old water pump puked i did not include this in total price since most guys i know have em already on their jeeps not sure if it makes a difference sometimes i wonder if its more issues )



Few details on the jeep. CJ 7 mildly warmed 401, t18 D300 4.5" spring lift, 35's 8274 winch in front 1" body lift.

I have a 1" body lift which put the stock 7 blade 17" fan right close to the shroud. To clear a bigger fan and to healp with geometry when lifting the tranny I moved the MORE motor mounts up and that created ample room clear the 18" caddy fan in stock shroud. Since i was going for a flat belly pan with my clocked dana 300 things needed to be shifted little any ways i re=drilled the more mounts 7/8" up and 3/8" for ward sliding the motor slightly ahead helped with valve cover clearance at the fire wall, moving it up allows you to continue using the stock radiator shroud. My flat belly pan is actually 5/8" below my frame but that is fine for what i wanted.

I too had some overheating issues w/ my CJ7 w/401. After messing around with numerous combos I found a very simple solution. I use a 4 core brass radiator and a 19" flex-a-lite fan (part #5719). I had planned to use the stock shroud but I was having trouble getting it to line up right, so I tried it without the shroud and it works just fine so I left it off. I don't use a fan clutch either, just a solid spacer. The fan moves enough air to pick up weiner dogs and suck them through the grill.

Without the shroud, I'm sure the 20" fan would fit and move even more air. I've never had a cooling problem once I installed this fan. The fan isn't rated for high rpm, but I very rarely see 4500+ rpm. I'm sure I'm losing some hp by driving this big old prop, but I could care less. It works like a champ.