Fan or water pump?

[gbarber]

My 289 has a new 4 row radiator, fan shroud, a stock 7 blade fan with a new clutch, and a newer stock replacement water pump. Since I rebuilt the engine a year ago (1500 miles), I have had some cooling problems when idling. On the freeway its fine (180*). I put the fan shroud yesterday hoping this would solve the problem, but after taking a short drive, then allowing the car to idle at about 800 RPMs for 10 minutes, the temperature rose to near 220*.
I then ran the car in neutral at 2000 RPMs for about 3-4 min. The temperature dropped to around 200*. If I would have driven the car, the temp would have dropped to 180* within a mile.
My question is does this drop in temp while idling at a faster RPM come from the fan spinning faster, or is it from the water pump moving more coolant? Or is simply a result of both. I was just wondering if one would have more of an effect than the other.

 

[Pbum5]

do you have stock or underdrive pulleys?

 

[faultlessfocus]

do you have stock or underdrive pulleys?

That's a good question. Sounds like it isn't pumping enough at lower RPM's?

 

[gbarber]

The pulleys are stock.

 

[2nd Mustang]

Is the belt slipping or maybe not tight enough? Fan too far from radiator? Your setup sound like it should be more than adequate in the cooling department.

 

[usedtobe 67p51d]

timing? lean idle circuts?

 

[gbarber]

The fan is very close to the radiator. There is only 1/4" between the radiator and the fan. The belts are tight.

 

[65ShelbyClone]

I tend to think its your fan since its the only part of your cooling system that is not new. I imagine the stock fan doesnt have alot of pitch to the blades even if there are seven of them. The blades also tend to flatten out after 39 years of flexing(its a factory flex, right?). I had a 65 289 with a three row high-efficiency rad from NPD, six blade Flex-A-Lite, and a fairly lean tune. I could drive it around in 105* heat and could watch the t-stat open and close on the gage. I cant remember the last time I heard of a (good)stock water pump not moving enough coolant at low rpm. Other than that, check your timing and carb like others have said.

 

[gbarber]

The timing is set at 12* BTC. I tried to tune the idle on the carb as directed by Edelbrock. It could be lean.
I'll look into the fan itself. It is an original piece, and I'm sure, as pointed out, it probably has lost some it's pitch over the years. Although it appears to be in good shape and all of the blades are pretty close to being at the same pitch, I have no idea how much it has changed over the years.

 

[CochinoFilipino]

I'm thinking that a 1/4" is too close and it is messing with the airflow at low RPM.

 

[2nd Mustang]

Is the hood closed when you test it at idle for 10 minutes? If yes, try opening the hood and see if it idles cooler, then you'll know if it's an air/water flow problem. I just recalled this problem on my old Camaro with a small radiator. It would run 200 degrees plus with the hood down, but when I opened the hood at idle, it would cool down and stay cooler, thus proving an air/water flow issue.

 

[gbarber]

The 1/4" is the most I can get because of the increased thickness of the 4 row radiator.
When I idled it for ten min, I had the hood closed.

 

[notny41]

Could you get a different spacer for behind the fan? I just changed my 13/16" spacer for a 2-5/8" spacer on my 289. Let me know if you need the shorty.

 

[gbarber]

My car has A/C, and has a clutch fan. I have never really looked into whether or not someone makes a shorter clutch. I bought this one as a stock replacement from NPD.

 

[WORTH]

My car has A/C, and has a clutch fan. I have never really looked into whether or not someone makes a shorter clutch. I bought this one as a stock replacement from NPD.

the fan clutch could be slipping, when it's hot at idle and you shut it down does the fan spin for a second before it stops, if it does it mah not be fully engaging.

 

[66Runt]

... Since I rebuilt the engine a year ago (1500 miles), I have had some cooling problems when idling.

Engine was running cool before being rebuilt?
Did it run cool even with the A/C on?

What was changed during rebuild (not after, in the attempt to get it to run cooler)?

On the shroud, make sure at least half the fan blade is exposed.

Scott

 

[gbarber]

When I bought the car, the engine was a wreck. I only drove it about 5 miles, after I trailered it home, before I completely tore it down. The A/C was disconnected.
After the rebuild, I struggled with cooling until I changed the fan clutch and the radiator at the end of last summer. I could drive the car pretty much anywhere without cooling issues. I could only run the A/C if I was on pretty open roads. Stop and go driving would cause over-heating. (This was in September after I fixed the A/C and replaced the radiator. Not 90* weather). In the rebuild, not too much changed. The block is now .040 over, and I put on a set of GT-40 heads.
Recently, it seems the car gets hot while sitting still. It isn't a big deal normally, but one day last week I had the family in the car and we went throught a restaurant drive-thru. Once in line, the temperature rose very quickly. I couldn't get out of the line because it runs between two buildings. The temp rose to 220* before I got out on the road. Within a mile of 55 mph driving, the temp was back at 180*.

 

[grego37]

if your car runs hot while idleing ,but runs cool at 30mph+ speeds, you should look into the following:

Fan issue, not pulling enough at idle, better fan and shroud. or Upgrade to a good electric fan.

Carb air/fuel mixture (too lean?).

W/pump should be overdriven on a street car. (smaller dia than crank pulley)

good luck

 

[2nd Mustang]

The temp rose to 220* before I got out on the road. Within a mile of 55 mph driving, the temp was back at 180*.

My Camaro used to do this too. It ran right about 200 degrees all the time and got to 220 with the air on when in stop and go driving. It had a single core radiator so expected as much, but it really didn't hinder the car any. I think as long as you have the proper 50/50 mixture, you're probably okay. At 220, my Chebie never did boil over, except when I had a leaky radiator.

 

[66Runt]

Lack of airflow over radiator core

Sure sounds like a lack of airflow over the radiator core. Do the test Worth mentioned. Your fan shroud should cover, and allow, air to be drawn from the entire core (like stock 66 shroud). The fan blade needs to be at least half way exposed, and you need about 1/2" between the fan blade and the edge of the shroud for clearance to get the best flow.

You should be getting a good strong breeze behind the fan even at idle. If not there is your issue. Any way you can try a different fan/spacer assembly?
You're not running any kind of bug screen or billet grill, big fog lights or anything else in front of your grill are you?