Radiator flow questions on '67 390 GTA - Ford Mustang Forum
LinkBack Thread Tools
post #1 of 6 (permalink) Old 11-11-2013 Thread Starter
Omaha Bill's Avatar
Joined: Jul 2013
Location: Omaha
Posts: 7
Radiator flow questions on '67 390 GTA

I Have '67 390 GTA. I bought car where previous owner had people literally replaced/touched every part on car in totall restoration. Have been having some cooling issues that we are working on--- installed new thermal fan clutch, 7 blade fan and fine tuning the ignition. While running engine in garage at idle with radiator cap off, were very surprised to see rapid fluid flow inside radiator. The water pump appears to be stock. We are concerned that flow is too rapid and fluid isn't in radiator long enough to "be cooled". This normal? Thoughts? Thx Omaha Bill

Omaha Bill is offline  
Sponsored Links
post #2 of 6 (permalink) Old 11-11-2013
jaki30's Avatar
Joined: Jul 2013
Location: Williamsburg
Posts: 98
Thermostat issue?

Rapid flow into the radiator usually indicates a missing or stuck open thermostat. Normal operation is for the stat to stay closed until it's operating temp point is reached (somewhere around 160 on the older cars). It opens and lets in the cooler water from the radiator. This cause the stat to close and the process starts all over again.
If the water is not cooling down in the radiator, this could cause the symptom you describe as the stat is open due to high water temp. Shut the car off and feel the front of the radiator from left to right, top to bottom. There should be no 'cold spots' within the radiator.
One other issue that would cause high water temps with a properly operating stat would/could be a head gasket problem.

jaki30 is offline  
post #3 of 6 (permalink) Old 11-12-2013
BOSS Member
Classic Member
rex1965's Avatar
Joined: Jan 2010
Location: Pittsburg
Posts: 4,556
To check the thermostat, start the engine when cold, let it run with the hood open, use your hand and feel the heater hoses, the inlet to the heater core (bottom hose on the firewall) should be warming up, if you touch the top radiator hose at the radiator it should still feel cold, if it is feeling warm also, and near the same temperature as the heater hose, then the thermostat is open or missing, neither is a good condition. IF you have a good thermostat, When the bottom heater hose is getting hot, the top radiator hose should be getting hot near the thermostat housing but not so much at the radiator, when the thermostat finally opens, then the top radiator hose will be hot all the way across and you should feel warm to hot air blowing from the radiator. Good Luck.
rex1965 is offline  
post #4 of 6 (permalink) Old 11-12-2013
PONY Member
seph10's Avatar
Joined: Feb 2012
Location: Peach Bottom
Posts: 500
sounds like it could be a thermostat issue,,hang it in a pot of water and heat the water up,,,you should see the thermostat open at about the temp. stamped on it,,do this with a new thermostat also,,I have gotten bad ones before,,
seph10 is offline  
post #5 of 6 (permalink) Old 11-12-2013 Thread Starter
Omaha Bill's Avatar
Joined: Jul 2013
Location: Omaha
Posts: 7
Guys, appreciate your responses. I mis spoke when I commente about rapid flow at idle implying that thermastat was stuck open. The rapid flow is occuring after the thermastat is open. So my question, is rapid flow something normal/what you have seen in your 390's? Also, where on your temp gauges( 1/3, 1/2, 3/4) does needle usally end up when operating on 60 degree days and on 75 degree days? Thx--Omaha Bill
Omaha Bill is offline  
post #6 of 6 (permalink) Old 11-12-2013
BOSS Member
Beechkid's Avatar
Joined: Apr 2013
Location: SoCal
Posts: 4,346
One of the greatest impactors that has come to be are the "high-flow" replacement water pumps that were introduced (and still here) in the late 70's......although 99% of it is a better impellor design, it did increase the flow rate of coolant in the system.....Now originally, the increased flow was 3% IIRR which still gave a good amount of time for the coolant to absorb the heat and expell it at the radiator but over the years & especially in the mid 80's the engineers upped the design again and well, that's when we all starting to see our engines running warmer (you also have to remember at the time these same style water pumps were still in use on the new vehicles- which were designed for the increased flow). On our Mustang the flow was so great that it would cause the radiator cap seal to "lift" under higher rpm causing fluid to expell, which we addressed with an overrflow/recovery tank (had to home-build that one at the time), which today is a common standard so to speak.
The increased flow/cooling issue is really nothing new though, as with the flatheads- had the same/similar problem caused in part by increased HP/TQ & speed- the solution was to install a giant washer (restrictor) at the upper radiator inlet- this slowed the flow to allow greater absorbsion/cooling.
IMHO, it really all depends on the radiator specs if it was of a design to 'handle" that specific engine, etc...you just are not going to know until you take it out for a drive, but from they way it sounds as you have described, the "assembler" didn't just buy parts off the e-net that said it fit x-car with x-engine and actually did their homework selecting each component specifically (which if you don't do even on new cars will get you into trouble).

Member: Never trust a person over 40 who drives a Chevy club
Flatheads ain't so bad!
Certified backyard mechanic I & II
Beechkid is offline  
Sponsored Links

Quick Reply

Register Now

In order to be able to post messages on the Ford Mustang Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a VALID email address for yourself, otherwise you will not receive the necessary confirmation email needed to confirm, validate and activate your new AFM member account.

Failure to provide a VALID email address, will result in the cancellation of your new AFM member account registration.

Email Address:


Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are On

For the best viewing experience please update your browser to Google Chrome

Search Engine Friendly URLs by vBSEO 3.6.1