Overheating in Drive

If it's mechanical, electrical or just downright confusing, this is the place to find and share answers.
'69TwoToneXR7
Registered Member
Posts: 68
Joined: 11 Dec 2014, 18:59

Overheating in Drive

Post by '69TwoToneXR7 » 10 Jan 2018, 14:44

Hello,

I have a 1969 351W 2bbl Cougar. The engine was rebuilt and bored 0.30 over. The car has started experiences overheating problems when stopping after driving. I have replaced the radiator to a 3 row aluminum stock looking radiator from WCCC. The head gaskets were just replaced. The water pump, fan clutch, thermostat (180F), water valve for the heater have also all been replaced. The car fires up nicely and the temp gauge reads at 5/8 when the thermostat opens. I had the engine taken back to the machine shop that rebuilt it and he couldn't find a problem with it. I then took the car back to the transmission shop and they couldn't find a problem either. I was told that the inside portion of the torque converter in the car (I have an FMX) is always engaged even when stopped at a red light. In 1978 or so they invented a locking plate that disengages at red lights so that the inner part is not engaged anymore. When driving the car runs beautifully. The temp creeps up at stop lights in drive and that is what makes me nervous. The trans fluid is still bright red and there is air flow when the car is stopped. In park the car can idle for a while and nothing will happen, but in drive and after driving at speeds of around 55 for 30 minutes the temp slowly creeps up. There aren't any leaks in the system and at this point I'm at a loss. Any ideas would truly be helpful.
The upper radiator hose is 198.6 and the lower is 170.4.

User avatar
xr7g428
Site Admin
Site Admin
Posts: 4250
Joined: 23 Dec 2010, 21:02
Location: Cave Creek, AZ
Contact:

Re: Overheating in Drive

Post by xr7g428 » 10 Jan 2018, 17:32

Both issues tend to point to a water pump problem. "The temp creeps up at stop lights in drive" "after driving at speeds of around 55 for 30 minutes the temp slowly creeps up"
Bill Basore, Editor / Publisher
Legendary Cougar Magazine
Currently in the Cat House
'67 XR7 GT 390 4 speed, AC, AM FM, Lime Frost Green
'68 XR7-G 428CJ C6, Tilt-Away, AM, Black Cherry
'68 XR7-G 390 4 speed, Sunroof, Cardinal Red
'68 XR7 GT-E 427 C6 AM Cardinal Red
'68 XR7 resto mod 351W, soon to be AOD, Black Cherry

User avatar
CougaDan70
Registered Member
Posts: 300
Joined: 19 Sep 2013, 19:04
Location: Montréal, Qc

Re: Overheating in Drive

Post by CougaDan70 » 10 Jan 2018, 19:00

Temp. at 199 at exit of upper hose does not seem to me as overheating...
See what mine does after stop and go in heavy traffic (early 1970 = same engine as you) and it drives really well:
viewtopic.php?f=3&t=8027&p=81983#p81983
Your gauge being at 5/8 when your Tstat opens seems too high to me, mine is at about 1/3 when Tstat opens.
You most probably know, but temp of the rubber hose can not be measured accurately with a laser thermometer, you need to point at the metal on top of the radiator right next to the exit point (see pic in above link).
1970 Vert 351W / FMX with PB & PS, that's all there is but man am I happy!
Dan, Montreal Qc.

User avatar
TheRktmn
Registered Member
Posts: 278
Joined: 18 Oct 2011, 15:59
Location: Goldthwaite, TX
Contact:

Re: Overheating in Drive

Post by TheRktmn » 11 Jan 2018, 09:32

Just for reference, my 69 runs just under 1/2 with a 180* thermostat, about 5/8 with a 195*.
Bob

CCOA Member #8195
'69 Cougar XR7, 460/C6. Caution: This car fitted with optional Caution Fan Sticker option!
Internet Rule #6: Never confuse post count with expertise

Tachometers, Voltmeters, Plug & Play Headlight and Horn relay kits and more modernized innovations at
Rocketman's Classic Cougar Innovations: http://www.rccinnovations.com

I am usually parked at The Curb: http://www.thecurb.org

User avatar
JETEXAS
Registered Member
Posts: 323
Joined: 06 Aug 2017, 07:26
Location: Houston
Contact:

Re: Overheating in Drive

Post by JETEXAS » 11 Jan 2018, 09:38

If you have a clutch fan, make sure the clutch is still engaging. You need that airflow over the radiator when stopped. If you don't have a fan shroud, that might help as well.
Image

User avatar
wish
Registered Member
Posts: 128
Joined: 05 May 2017, 13:12

Re: Overheating in Drive

Post by wish » 11 Jan 2018, 10:04

The fan and shroud were my first thoughts as well, though I'm curious what other changes happened around the time the overheating started, if nothing else I might suspect the sending unit going bad.

Here's a thread on sending units that might be worth a read :

viewtopic.php?f=3&t=8027
Just my $.02
wish
69 Cougar, That 70s Truck, 84 Cherokee Chief 2dr, 88 Grand Wagoneer, 95 Grand Cherokee,96 Mustang

User avatar
Royce
Registered Member
Posts: 1020
Joined: 22 Oct 2011, 07:14
Location: Dallas, TX

Re: Overheating in Drive

Post by Royce » 11 Jan 2018, 10:36

20 degree difference between the upper and lower radiator hose sounds like the radiator is shot, or the fan has no fan shroud, or the timing is way off. I would start by making sure that you have a fan shroud, then check the timing with a dial back timing light to see what's really happening.
1968 GT-E XR-7 W code 427 Augusta Green / Saddle
1968 XR-7 R code 428CJ Ram Air Red / Black
1910 Model T Ford Touring Red / Black
1914 Model T Touring Maroon / Black
1915 Model T Ford Touring Black / Black
1917 Model T Ford Torpedo Runabout Green / Black
XR7-G Registrar

'69TwoToneXR7
Registered Member
Posts: 68
Joined: 11 Dec 2014, 18:59

Re: Overheating in Drive

Post by '69TwoToneXR7 » 12 Jan 2018, 22:08

I do have a fan shroud and the radiator is brand new. I tested the sending unit with a multi meter when the engine was cold (air temp was 55-60F) with the multimeter set to 2,000 ohms. The reading when cold was .357 which was 357 ohms. Is that a normal reading for a cold engine? The fan clutch engages and disengages when it should and its also brand new. I did notice that if I put the car in park after its been run a little while and step on the gas to increase the rpm to about 1,200 the gauge drops a little.

User avatar
CougaDan70
Registered Member
Posts: 300
Joined: 19 Sep 2013, 19:04
Location: Montréal, Qc

Re: Overheating in Drive

Post by CougaDan70 » 13 Jan 2018, 02:44

'69TwoToneXR7 wrote:
12 Jan 2018, 22:08
... I did notice that if I put the car in park after its been run a little while and step on the gas to increase the rpm to about 1,200 the gauge drops a little.
That is because more air is pulled through the rad at higher rpm. To optimise the amount of air that is pulled through the rad at any given (lower) rpm, the fan shall sit 1/3 in the shroud and 2/3 ahead of it toward the engine. If the fan sits too deep in the shroud, efficiency of the shroud is tremendously reduced.
1970 Vert 351W / FMX with PB & PS, that's all there is but man am I happy!
Dan, Montreal Qc.

canted 393
Registered Member
Posts: 31
Joined: 21 Sep 2017, 05:44

Re: Overheating in Drive

Post by canted 393 » 13 Jan 2018, 06:27

Check your waterpump pulley ratio, on the street a waterpump should turn 10-15 % faster than the crank pulley. Racing is 1 to 1. You might have to go to a smaller pulley on the waterpump to spin it faster.

Post Reply