Overheating after rad trans cooler bypass

[Bigal75]

Does it heat up at idle or only at highway speeds. The lower temps, we're they with this rad or another? Have you had the gauges worked on?

 

[68 Sport Satellite]

All is the same before and after the trans cooler. Same gauges with no work done, same rad...

Another FBBO member (Threewood) installed this same trans cooler also with a 22" rad and big block 727 and he's having no issues. So here's what I did differently and need to remedy:

1) External Trans cooler mounted on driver's side instead of passenger side: Not sure if this matters, but my rad hoses are on driver's side...
2) I had bypassed the internal rad cooler. I will hook back up in series as he outlined.
3) External trans cooler mounted with both ports facing up. I will now mount with ports sideways.

Does it heat up at idle or only at highway speeds. The lower temps, we're they with this rad or another? Have you had the gauges worked on?

 

[Bigal75]

Ok thanks for the info. How much of a gap do you have between the cooler and your rad? It sounds like an airflow issue since you've installed the cooler.

 

[68 Sport Satellite]

2.5" between face of trans cooler and face of rad

 

[HEMI-ITIS]

This one is a head scratcher,,,,,what is the timing set at??

 

[68 Sport Satellite]

I think I may have found the problem, but need to test and confirm. Both the Griffin radiator website and a few other places mention to keep the gap between the radiator and the external trans cooler less than 1/2" to ensure air flow through the cooler and rad. Otherwise, the air can go AROUND the cooler and not through it. My gap is 2.5". Stay tuned...

 

[Bigal75]

Hmm. I have 2 or 3 inches between mine. Could be the problem since you weren't having issues before.

 

[CoronetDarter]

Dwayne - When I bought my Derale rad cooler the tech highly recommended installing the cooler in series with the radiator, for all the reasons mentioned above. The cooler splices into the output side of the rad, not the pressure side. On the Coronet that happens to be the drivers side so it's fun negotiating around the oil filter. My resto page has close up pics; I can PM more if you need.

 

[Yatzee]

Curiosity led me to explore the cooling problem you have and weather it is associated with the trans cooler. I like the idea of bringing it closer to the rad surface but this got me to wondering. Cars with A/C have the condenser mounted really close to their rads and one has to wonder how warm air coming off the condenser through the rad can really be an efficient way to cool the motor especially when A/C is generally run in very hot weather. It stands to reason that there has to be a huge volume of air being moved across both heat exchangers to cool the engine and remove heat from the freon in the A/C system. You shouldn't really have an issue with either the rad or the tranny cooler unless there was partial blockage, poor flow of air or a seriously hot engine compartment. Perhaps you could lower the level in the rad tank and observe the coolant flow as the engine warms up. It shouldn't boil over if your about 2" below the fill neck but you will deffinitely see flow. If it does burp up, you have air pockets in the block or air being introduced to the coolant by some means. Obviously easier to see on cross flow rads where the filler is on the return side of the rad. As tranny cooling goes I found this tid-bit in a service booklet for tranny repair shops:

Fluid Temp VS. Transmission Life Expectancy

175°F = 100,000+ miles
190°F = 90,000 miles
210°F = 55,000 miles (Pressure Drops)
230°F = 25,000 miles (Valves Stick)
250°F = 17,000 miles (Varnish Forms)
270°F = 4000 miles (Seals & Clutches Burn)
300°F + = TRANSMISSION FAILURE

Now honestly, how many car owners actually know their tranny temps or for that fact have a fluid temp guage in their cars? Considering the cost of rebuilds you would think it was one of the most important pieces of data for the driver to know. You know when an engine overheats or your oil level/pressure is low but not what's going on in one of the most important drivetrane units. Seems we all have the means to save a good chunk of change. I recently installed a Painless
F5 Dual Fan Controller to control the Spal 10 inch fan mounted atop my Derail tranny cooler which is mounted under the car. The controller supports PWM and runs the fan at what ever speed is required to maintain a set fluid temperature. They were really made for radiator cooling fans but work just fine in many applications. I set the controller at 180 and monitored the operation with a laser temp gun. You could hear the fan speed up as the sensor detected rising temps in the tranny fluid and then drop back down as it reached it's set temp. On the highway an indicator light showed that the fan cycled for very short periods as the air under the car took the heat off the exchanger. I still can't help but wonder how transmissions lasted as long as they did with just a looped 5/16 pipe mounted in the lower radiator tank. Praise the Lord it must have been a miracle.

 

[bm02tj]

As mentioned by other people build your self an effective fan shroud so you get your air flow then work from there

 

[68 Sport Satellite]

We all know that we all need a shroud.

The purpose of this thread though is to find out why the drastic change from before external trans cooler to after install of external cooler. Didn't have a shroud before and don't now. I will add a shroud soon for sure, but I still need to address this problem. There is a big difference from before and after and I've almost got it solved.

As mentioned by other people build your self an effective fan shroud so you get your air flow then work from there

- - - Updated - - -

I came across an article today describing my exact issue and then consulted both Griffin Radiators and Derale. Air flow will get all messed up and not pass through the trans cooler or rad if the trans cooler is mounted too far away. Instead it will flow up and around it. Since the trans cooler is mounted in front of the rad, this makes sense. They recommend 1/4-3/8" gap, with 1/2" being the max.

This is the most logical explanation I have come across so far. When I get time this weekend I'll modify the bracket and run it again and see what's what. Thanks for everyone's help and stay tuned...

 

[bigmanjbmopar]

Convert stall speed more or less than what was in there before?

 

[68 Sport Satellite]

EXCELLENT QUESTION!

This thing originally started due to a converter change....

I had built the 451 and ordered a stage II 727 from Cope Racing and a 2600-2800 stall PTC converter as recommended by PTC for my car specs.
Installed it and no leaks or overheating.
The trans was foot brake flashing to 3500 and although it ran great at highway speeds, it felt like the converter was much higher than 2800.

Fast forward a few months:
With the help of DPstark and Meep-meep, I swapped the converter for a 2000-2200 stall PTC converter, which is what's in it now. Much better driveability and foot brake flashing to 2000, however the trans started leaking from the bell housing vent. I then discovered that my kickdown was not engaging because WOT at the pedal was not wide open throttle at the carb. A little bend of the lever under the throttle pedal and now I have WOT and kickdown. (maybe the 2800 stall converter would have flashed lower if the kickdown was correct in the first place? That's a whole 'nother discussion!)

OK, now where I'm at is I installed the external trans cooler and no more trans fluid boil over out of the bell housing vent. BUT - now I have big time engine temp overheating. I'm hoping with better air flow due to a smaller gap between the rad and trans cooler engine temps and trans temps will become happy once again.

Convert stall speed more or less than what was in there before?

 

[hangn0ut]

Do yourself a favor and get rid of the air in your radiator. And go with a coolant recovery bottle.

 

[CoronetDarter]

EXCELLENT QUESTION!


I'm hoping with better air flow due to a smaller gap between the rad and trans cooler engine temps and trans temps will become happy once again.

I'm betting that's going to make the difference. BTW, what gear ratio are you running in the diff?

 

[pentahead]

I think your timing needs a faster curve as the tranny fluid was probably masking the issue.
If you can not get the motor/rad straight all is for not.
Have thought about A/F mixture too? Lean or rich will also mess with you.
Perhaps all is ok but your C/Ratio is to high for your rad to cool?
Time to think outside the box.
Good luck

 

[bm02tj]

Moving the trans cooler closer to the rad will help the trans cooler dump more heat but is still blocking air to the rad and with out the shroud to create better air flow nothing is going to change

 

[68 Sport Satellite]

After starting the car, if it sits and idles for 20 min, it stays below 200F. If I put it in gear and drive down the street and back for less than a minute, the temp climbs to 225F and stays there whether stopped or moving.

Does it heat up at idle or only at highway speeds. The lower temps, we're they with this rad or another? Have you had the gauges worked on?

- - - Updated - - -

Thanks, I've already got the overflow bottle installed. With that installed, how far up should I fill the rad? I was always told leave 1-2" from the top of the filler neck.

Do yourself a favor and get rid of the air in your radiator. And go with a coolant recovery bottle.

- - - Updated - - -

3.55's with 28" rear tires. Spins at 3000 RPM at 65 mph

I'm betting that's going to make the difference. BTW, what gear ratio are you running in the diff?

- - - Updated - - -

I am with you for the most part. Back to the beginning though - in the beginning i had no engine overheat or trans boil over leaking and I had no shroud, no external trans cooler (only internal rad) and a different slightly higher stall converter. Why would a tighter lower stall converter cause this issue? More load on the motor? I thought the looser converter higher stall would cause more heat. Nobody else has ever had this happen?

Moving the trans cooler closer to the rad will help the trans cooler dump more heat but is still blocking air to the rad and with out the shroud to create better air flow nothing is going to change

 

[CoronetDarter]

The higher stall converter definitely generates more heat, so all things being equal installing a low stall converter should not be the problem. And as you say, if after the car warms up at idle and stays below 200 then it's not an airflow issue.

 

[cdr]

sounds like the radiator is plugged up.