Ford 302 rapid temperature rise at idle

[UKjohnnycobra]

Hi all, I'm looking for some advice on engine cooling.

I have a stock Ford 302 in my Cobra which I currently run with a 160F thermostat. The engine runs at around 180F when moving, but the minute I stop at traffic lights or in slow moving traffic, the temperature rises very quickly (less than a minute) to 200F or greater and the elecric fans can just about stop it going above 200F but cant get it back down to close to 180. When I get moving at speed again the temperature comes back down to 180F after a couple of minutes. The car is not boiling over but this is very annoying as it means that the fans are on any time I am stopped and for several minutes after I drive away
I have a new Griffin two row aluminium rad which is more than enough cooling. I have two 12 inch fans which are definitely blowing in the right direction. The themostat is new and drilled at 12 oclock. I have swapped out the stat and the problem persist with different temperature stats. The water pump is new. The problem existed with the old pump too. I have a bypass hose in place. There is no air in the system; it has been filled and burped multiple times an I can check the head fluid level through a fitting on the manifold. The block, heads and rad are completely filled. I use a 50/50 mix. I have flushed the system multiple times.

I am thinking that maybe the pulley ratio is wrong and the pump is not turning quickly enough at idle. I have a 6inch crank pulley and a 5.5 inch water pump pulley. Any thoughts on this? What are the correct pulley sizes/ratios?

Thanks in advance

[FWB]

Originally Posted by UKjohnnycobra

Hi all, I'm looking for some advice on engine cooling.

I have a stock Ford 302 in my Cobra which I currently run with a 160F thermostat. The engine runs at around 180F when moving, but the minute I stop at traffic lights or in slow moving traffic, the temperature rises very quickly (less than a minute) to 200F or greater and the elecric fans can just about stop it going above 200F but cant get it back down to close to 180. When I get moving at speed again the temperature comes back down to 180F after a couple of minutes. The car is not boiling over but this is very annoying as it means that the fans are on any time I am stopped and for several minutes after I drive away
I have a new Griffin two row aluminium rad which is more than enough cooling. I have two 12 inch fans which are definitely blowing in the right direction. The themostat is new and drilled at 12 oclock. I have swapped out the stat and the problem persist with different temperature stats. The water pump is new. The problem existed with the old pump too. I have a bypass hose in place. There is no air in the system; it has been filled and burped multiple times an I can check the head fluid level through a fitting on the manifold. The block, heads and rad are completely filled. I use a 50/50 mix. I have flushed the system multiple times.

I am thinking that maybe the pulley ratio is wrong and the pump is not turning quickly enough at idle. I have a 6inch crank pulley and a 5.5 inch water pump pulley. Any thoughts on this? What are the correct pulley sizes/ratios?

Thanks in advance

fan shroud? are there spaces around the rad' that air can get thru without going thru the core? it takes quite a bit of cfm to pull the air from the nose to the rad'. sometimes two fans is more restrictive than one large one.
post some pics....maybe we can see something your missing....

Fred

[elmariachi]

Your engine and cooling system both sound okay, it just sounds like the cooling system lacks the capacity at idle to cool the coolant. The value of a fan shroud as mentioned by FWD is enormous, don't discount it. I would suggest you get a $60 infrared temp gun like this Micro Temp MT-PRO - Spark Industries Micro Temp Digital Infrared Pyrometers - Overview - SummitRacing.com and check your upper and lower radiator temps and check temps in the path of the fan and then outside the fan path. If you don't see 30-40 degree reductions from the entry and exit point if your radiator, your fan/shroud isn't doing the job. And if the temps outside the fan path are considerably higher, then the shroud or lack thereof is likely a contributing factor.

As for pulley size and pump circulation, I wouldn't go there yet. If you start trying to circulate the water faster, you lesses the amount of time it sits in the radiator to be cooled.

[marco454v8]

Hi Johnny,
I've got the same issues, I've just ordered the twin fans from finishline to supplement the two 12" fans I've got behind the rad. I'll let you know if it improves things. I have 100 deg c in slow traffic up to 110 if stationary.
Another thing I saw was an electric water pump in addition to the mechanical to keep the flow up at idle;The Davies Craig EWP115 electric water pump from MAW Solutions Ltd

Mark

[olddog]

Originally Posted by UKjohnnycobra

I have a stock Ford 302 in my Cobra which I currently run with a 160F thermostat. The engine runs at around 180F when moving.

I have swapped out the stat and the problem persist with different temperature stats.

Gauge reading 20 over T-stat. Are you sure the gauge is correct?

[UKjohnnycobra]

Thanks for the inputs, guys.

FWB: I dont have a shroud. I'll post some pics later so you can see. Because its a fairly uncommon car, if a shroud is needed I'll have to make one. The shroud would force air entering the nose through the rad, so its like a cone that fits in front of the radiator, right?
Elmariachi: I have an IR thermometer. Ill check the delta between the top hose and bottom. If I remember, when I looked at this before, it was about a 20F difference (seems low to you?) but I'll confirm.
Marco: thats exactly what I see! let me know how it goes (also, my guages are all in deg C but i convert them for the discussion)
Oldog: i dont think its the gauge because it runs at the right temp when the car is driving. Also it should read higher than the stat, no? Once the stat is open by definition the temperature is 160F or greater.

[jhv48]

No, the shroud fits over the back of the radiator and, in conjunction with one or two PULLER fans, sucks air past the radiator and into the engine compartment.

It sounds like you have two pusher fans mounted in front of the radiator. If so, they are much less efficient than two puller fans installed behind the radiator along with a shroud.

Could very well solve your problem.

[olddog]

Assuming the radiator has plenty of capacity to cool, I would expect the temp to run much closer to the T-stat rating. If you had a 195 T-stat would you expect the temp to run 215 down the road? My 347 runs 185-190 down the road with a 195 T-stat. In town it runs 195. I cannot say my gauge is accurate, as I have never checked it. However over the years, my daily drivers all seem to read close to the T-stat rating.

[Bob In Ct]

Is the gauge accurate?

Bob

[elmariachi]

Originally Posted by UKjohnnycobra

Elmariachi: I have an IR thermometer. Ill check the delta between the top hose and bottom. If I remember, when I looked at this before, it was about a 20F difference (seems low to you?) but I'll confirm.Oldog: i dont think its the gauge because it runs at the right temp when the car is driving. Also it should read higher than the stat, no? Once the stat is open by definition the temperature is 160F or greater.

On my big block car I have a 180*F t-stat and the temps are 190*F on the top hose and 145*F coming out the bottom. This after installing the infamous $50 Taurus shrouded cooling fan, which moves 3000 cfm on low speed and something north of 4k on high.

Fan discussion here: Taurus Cooling Fan Install

Use the temp gun on your manifold or wherever your gauge sender is mounted and that will give you a good idea of your dash gauge accuracy.

[UKjohnnycobra]

Thanks again, all. It may be a couple of days before I can test these ideas and post pics as I will be travelling for a couple of days. I'll bump this thread later.

[DAVID GAGNARD]

Originally Posted by UKjohnnycobra

Thanks again, all. It may be a couple of days before I can test these ideas and post pics as I will be travelling for a couple of days. I'll bump this thread later.

If you have NO fan shroud at all, that is 95% of your problem.......at speed, air is forced thru the radiator, at idle,only the fans will pull air thru the radiator and without a shroud, they are operating at maybe 50% capacity......

Your pulley sizes are fine,being it runs at the temp it does on at speed, tells me your cooling system is fine....you just don't enough air coming thru at idle without a shrouded fan........

at idle,get out of the car, light a cigarette, put it in front of the radiator and see how much smoke is pulled thru, then put it on the side of the radiator and see how much smoke is going around the radiator instead of thru it, you may be suprised.....the fans will pull the air from on the path of the least resistance, which without a good fitting shroud, it will come from around the raditor instead of thru it.......
David

[SoTxButler]

I had this problem with a car that had a 351 in it. As soon as the car started to move, the temp would start down and then up again as it came to an idle.

Every time I opened the hood, the fan was running...so I never thought to check to see when the fan came on.

After changing the thermostat a second time, I installed a mechanical gauge and was watching the car idle and because I was watching the mechanical gauge, I noticed that the fan didn't turn on until after the temp went past 200 degrees.

I checked the thermistor in the radiator and found it to be defective, it was working and running the fan, but too late. So, air flow cooled while rolling and temperature rose while idling and the fan was turning. I installed a fan controller with a probe for the radiator and set it to turn on the fan at 180 and voila...fan starting turning at the right temperature and no more spiking temperatures at idle or slow speeds.

Check to see what temperature the fan starts running.

[Rick 427 Cobra]

Had a friend with the same issues. We looked at EVERYTHING. It turned out to be the water pump. Some rebuilts come with an impeller that looks like it came off an alternator. Cheesy stamped steel thing. Replaced it with a rebuilt with an original style cast iron impeller and all was good. Just not enough flow at low rpm.
Good luck

[Rick Parker]

Rick 427 Cobra above hit on a very good item. The OEM pumps in many instances used a cast iron impellor where many of the aftermarkets use a stamped steel which can cause all sorts of issues including cavitating.

Just another thing to throw in the mix: If you have electric gauges be sure the sending unit is the correct ohm rating for the gauge. Often they will function with the incorrect sending unit but the readings will be off considerably at one end of the scale. If you have a reasonable size radiator a 302 shouldn't heat up quickly at a light, (is the radiator clean inside??)

[UKjohnnycobra]

I just wanted to bump this and let you know that I think I may have solved the problem, and to thank you all for your input. I know you have been waiting all summer to find out how this ended!
I have an electronic temp sender unit. The sender location on the manifold is a 3/8NPT thread and the sender itself is a 1/8NPT. This means I use an adaptor, like this.
But, (and here is where I think the problem resides), because of the thread taper the adaptor doesnt fit all the way in to the location and the sender doesn't fit all the way in to the adaptor. The sender itself is barely touching the coolant.
So I cut off the final half inch of the adaptor, effectively lowering the sender into the manifold and deeper into the coolant. Result? The engine (apparently) runs much cooler when the car is moving and peaks at about 185 before the fans kick in and they now (apparently) bring the temp down just as they should.
In fact, with the 160F stat in CT in november the whole thing runs a little too cool, so I may go back to a 180F stat for the winter. Also I have ordered a new sender with a 3/8NPT thread so I can eliminate the adaptor altogether.
Yay!

[xlr8or]

Remember your thermostat only defines the minimum running temperature not the average or max.

[jhv48]

Put the 180 thermostat back in and leave it in year round.

[Rick Parker]

Generally a 289/302 will not quickly overheat at idle unless the radiator core is plugged, cracked head, or head gasket are compromised. Even an inefficient fan is not a big deal for a "little guy". Lastly be certain the radiator being used is of adequate size.

[marco454v8]

Originally Posted by marco454v8

Hi Johnny,
I've got the same issues, I've just ordered the twin fans from finishline to supplement the two 12" fans I've got behind the rad. I'll let you know if it improves things. I have 100 deg c in slow traffic up to 110 if stationary.
Another thing I saw was an electric water pump in addition to the mechanical to keep the flow up at idle;The Davies Craig EWP115 electric water pump from MAW Solutions Ltd

Mark

Well I can report, that I think the additional water pump did the trick. I did half an hour on track (Paul Ricard HTTT) revving to 5k, at the end I went straight to the on site gas station and sat at idle for ten mins, never reached 100°C /212°F, air temp around 25°C/77°F, so the craig davies was well worth the money! I just hooked it up to my fans, which I control from the dash.
Thought you guys might like the picture
Mark