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Overheating after rad trans cooler bypass

68 Sport Satellite

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Been running the new 451 with mild cam for 1250 miles now. Always had a temp of about 180-190 on the gage (which is supposedly solid state and calibrated by redline gauge works. Have been running an awesome aftermarket aluminum 22" griffin rad with trans cooler lines inside this rad. Works awesome.

However, due to a recent converter change causing the trans vent to puke fluid out of the bell housing, it was suggested to install a plate type external trans cooler which I did last week. In doing so I bypassed the rad trans cooler completely. Also added a rad overflow cannister. Rad fluid level is 2" from top of cap opening.

Now since bypassing the rad trans cooler and adding the external trans cooler, no more trans leak from bell housing. Score! However now my engine temp is very high!

I know 210 is not bad but that is the lowest it is now and it fluctuates between 210-230. Here is my gauge five min after startup today 6pm mild 65 degree evening in Northern California with dry cool air and car moving at 10mph image.jpg

Now here it is twenty min later driving for ten min at 40mph. It should be a LOT cooler. What gives? Since the trans cooler portion of the rad is now empty is the air inside getting things too hot? Should I run it in series instead?

image.jpg
 
Try filling to top. (you can not overfill it will burp extra into puke tank) As it cools and compresses it will pull from puke tank to keep radiator full to top. Dave
 
Thanks. Did that already. It ran even hotter so I removed some fluid to get it back to 2" from top

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I know there are other things to make run cooler, but what I am interested in is if anyone else has had an engine temp increase from installing external trans cooler and bypassing the one in the rad? It really surprised me.
 
Just a thought, maybe your transmission was puking fluid because it was absorbing the heat from the engine thru the radiator. I am running a 4200 stall on the street/strip and never overheated the trans bad enough to puke fluid. Is it a 2 or 3 core. My engine ran hot in traffic when I first built it and ran a stock 3 core, but switched to a new 3 core aluminum and never had any problems since. Also using the stock fan as I found an electric cannot keep it cool enough. Hope this helps. I went back and reread your post and saw the temp after 5 min warmup. You need to check the temperature at the thermostat housing with an infared thermometer and verify the gauge reading too. If it's not gurgling after you shut it down after your short cruise then I think the gauge is the problem.
 
It's strange- I was running a 2800 stall converter with same trans and motor and only internal rad trans cooler. Never any trans leaks or engine overheating. I switched to a 2000 stall converter and trans started puking. I thought it should be just the opposite and that a higher stall will produce more heat?

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Back to the original question - my external trans cooler is mounted on the drivers side in front of part of the rad. Could it be blocking enough airflow to cause this overheating issue? I have a 22" griffin aluminum rad 2 row with 1.25" tubes. Cooled great before and engine temps never over 190
 
I think you might have an airflow problem. Do you have a shroud? I didn't notice if you mentioned one above.

Bypassing the trans cooler shouldn't make much difference... Just hear me out about how the oem style trans cooler works... Heat transfer goes from hot to cold, so when the car is cold, the engine warms up faster than the trans, so the trans cooler steals heat from the coolant and actually warms the trans fluid. After the trans warms up, the tranny fluid becomes hotter than the radiator fluid, so heat transfer reverses and the radiator takes heat from the trans fluid and transfers it to the engine coolant.

That's it, so on a mild day after an hour of driving, the trans would be up to temperature on its own, so IMHO, no way is it helping your engine stay cool. The air in the empty trans cooler portion of the radiator is doing essentially nothing to help or hurt, it's just wasted space.

That's why I say you seem to have an airflow problem, because it seems to me the fan isn't sucking enough air through that trans cooler, so the radiator can't cool the engine. Also, as mentioned above, I wonder if you have an air pocket in the engine coolant circuit.
 
Thanks for the feedback. Ok, so I agree with the principal of how the OEM in-rad trans cooler works. What I'm wondering is if now that I've bypassed it and it's empty, is that dead air heating things up more than circulating fluid for the trans? It's only a 22" rad, but since it has 2 rows of 1.25" tubes, it's much better at cooling that a 3 or 4 row with smaller tubes.

I'm not trying to do everything on the list for better cooling that I haven't done yet - I know I still need a shroud if I can find one that fits. I've had 3 and they don't fit. This rad is a stock size replica with stock mounting holes. What I'm trying to figure out is why my engine is overheating now when it wasn't before.

Let's recap:

3 months ago:
2800 stall converter, aftermarket 22" griffin aluminum rad with 2 rows 1.25" tubes and internal rad trans cooler, no trans leaks, engine temp a steady 180-190.

Last month:
All else same as above, except switched to 2000 stall converter. Trans started leaking from bell housing. Engine temp still a steady 180-190.

Now:
2000 stall converter, same rad, now bypassed internal rad trans cooler and added external plate type trans cooler mounted on driver's side in front of rad (10" x 14" approx size). Trans leak gone. Engine temp now minimum 210 and normally stays between 220-230 even on the highway. Coolant is within 2 inches of top of rad just like before.

Theory #1:
Is the dead air in the internal rad trans cooler making the rad hotter overall than if it had trans fluid circulating through it?

Theory # 2:
Even though the paper test shows that fan is pulling hard through the rad with what seems like great flow, is it possible that since the external cooler is in front of a portion of the driver's side of the rad, that it's just enough to make things run a lot hotter?


I think you might have an airflow problem. Do you have a shroud? I didn't notice if you mentioned one above.

Bypassing the trans cooler shouldn't make much difference... Just hear me out about how the oem style trans cooler works... Heat transfer goes from hot to cold, so when the car is cold, the engine warms up faster than the trans, so the trans cooler steals heat from the coolant and actually warms the trans fluid. After the trans warms up, the tranny fluid becomes hotter than the radiator fluid, so heat transfer reverses and the radiator takes heat from the trans fluid and transfers it to the engine coolant.

That's it, so on a mild day after an hour of driving, the trans would be up to temperature on its own, so IMHO, no way is it helping your engine stay cool. The air in the empty trans cooler portion of the radiator is doing essentially nothing to help or hurt, it's just wasted space.

That's why I say you seem to have an airflow problem, because it seems to me the fan isn't sucking enough air through that trans cooler, so the radiator can't cool the engine. Also, as mentioned above, I wonder if you have an air pocket in the engine coolant circuit.
 
Is the trans cooler blocking air to rad if so move the trans cooler and put a electric fan just for the trans cooler
 
Running the cooler in series is a good idea since the radiator is set-up for it. Did you leave space between the trans. cooler and the front of the radiator? Pictures of the cooler install might help diagnose the problem.
 
First What's up glad to see you have it on the road.

Did you check the timing again after the converter change?

Where did you place the trans cooler? is it in front of the radiator maybe blocking a bit?


that cluster looks awesome! need way more pictures of it now!!

stop turning the phone sideways, do the right up and use panarama shot lol
 
I would run the trans through the rad then through your new cooler. Make sure you have a gap between the external cooler and the rad. Did you drain the coolant or anything while making these mods?

We're you running 180 with this rad?
 
Thanks for the feedback. Ok, so I agree with the principal of how the OEM in-rad trans cooler works. What I'm wondering is if now that I've bypassed it and it's empty, is that dead air heating things up more than circulating fluid for the trans?

No, it doesn't work that way. The engine is the sole source of heat here, so the coolant transfers the engine heat to the radiator and the radiator transfers it to the air as it crosses the radiator. That air in the cavity will pick up heat from the coolant until it eventually reaches about the same temperature as the coolant. At that time, heat transfer basically stops. Then Air rushing around that cavity will suck a little heat out of that air, bringing its temperature below that of the coolant. This triggers heat to flow from the coolant and back into the air. So the air really is pulling heat out of the engine too, it's just that air is a terrible heat conductor, so basically it's doing nothing.
 
Hmmmm, It is possible, just for grins...to take that external Trans cooler and route the output back thru the RAD, in effect putting the 2 in series? I know it's not what you wanted to hear, but if the RAD has dead space anyway, I don't see how it could hurt.

Example: Out of the Trans to the external cooler, then the output of the external cooler is then routed back into the RAD, then the output of the Radiator goes back to the Transmission. Hell, It's just a spit-balling idea.
 
I agree with you! The air is a good insulator but a terrible heat conductor, which is why I was thinking with fluid in there from the trans it may conduct heat from the rad better

No, it doesn't work that way. The engine is the sole source of heat here, so the coolant transfers the engine heat to the radiator and the radiator transfers it to the air as it crosses the radiator. That air in the cavity will pick up heat from the coolant until it eventually reaches about the same temperature as the coolant. At that time, heat transfer basically stops. Then Air rushing around that cavity will suck a little heat out of that air, bringing its temperature below that of the coolant. This triggers heat to flow from the coolant and back into the air. So the air really is pulling heat out of the engine too, it's just that air is a terrible heat conductor, so basically it's doing nothing.

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Yup, many people are running it this way. Don't know if it will make a difference, but it's next on my list.
Hmmmm, It is possible, just for grins...to take that external Trans cooler and route the output back thru the RAD, in effect putting the 2 in series? I know it's not what you wanted to hear, but if the RAD has dead space anyway, I don't see how it could hurt.

Example: Out of the Trans to the external cooler, then the output of the external cooler is then routed back into the RAD, then the output of the Radiator goes back to the Transmission. Hell, It's just a spit-balling idea.

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Here are photos of the trans cooler. It's mounted drivers side low with 8" space above to top of rad and 2.5" in front of rad.
image.jpgimage.jpg

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Today I changed my coolant and thermostat. No change. I even went from 50/50 prestone/water + water wetter to 25% prestone and 75% water with a bottle of royal purple purple ice (California Bay Area mild temps). No change. Still running at 210-220F

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I flushed the rad and added fluid slowly. Drilled 2 small 3/32" holes in my 180F stant super stat t-stat

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I bought an IR heat gun today and took the following readings, which confirmed my dash temp gauge is accurate and reading correctly.

engine block under car = 220F
Billet Aluminum T-stat housing = 190F (likely cooling off at the surface and not reflective of the coolant temp)
Cast Aluminum water pump = 180F
Transmission casing near trans support mount = 210F
cast iron exhaust manifolds = 550F
Cast iron heads = 200F

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Remember, before it was 180-190 ALL THE TIME.
 
I agree with you! The air is a good insulator but a terrible heat conductor, which is why I was thinking with fluid in there from the trans it may conduct heat from the rad better

For that to happen, the trans would have to normally run far cooler than the engine, even after hours of driving. Remember, that heat flows from hot to cold, so for the trans fluid to provide extra cooling, it would have to be significantly cooler than the engine. So if the engine is at 180*, the trans might have to naturally run at, say, 100*. Only then can it pull heat out of the radiator and provide some cooling. But if that were the case, that means the trans never needed a trans cooler to begin with and I'm not sure that's possible.

That's why I say it is probably an air flow issue. And don't forget, we all 'guessed' you didn't have a shroud based simply upon your symptoms - that in and of itself is a big indicator that we might be onto something.

Also, google 'homemade fiberglass fan shroud'. I made my own fan shroud using that method and it looks and functions GREAT.
 
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The first thing I would do is to temporarily remove the trans cooler from in front of the rad, twin the hoses temporarily and see if there is a noticeable difference in cooling. You're not going to toast your tranny for 10 minutes running. I'm not a fan of how you installed the trans cooler - it seems to be blocking a large area of air flow over the rad. Also, any heat generated by the trans moves vertically up the cooler ( the hottest point being at the top exactly where the hot coolant dumps in the upper tank ) which will happen with your installation. I prefer a cross flow trans cooler, say in the range of 5 x 18 mounted at least 2 inches in front of the rad and mounted horizontally. You don't need a gigantic cooler for a tranny - remember the cooling tube inside the rad doesn't have a large surface area and they worked just fine. One of the best coolers, and most popular, come off F150's out of the junk yards. Their compact, efficient, easy to mount and stack plated on the end manifolds. You can't imagine the heat you can generate in a truck tranny under load. Try clearing obstructions from the front of the rad and I think you'll see a dramatic change in cooling. Even a small 3 1/2 by 16 cooler will mount in a slanted orientation just in front of the cross member under and behind the front bumper yielding great cooling when moving and radiant off loading when standing still. As far as the performance of the cooling system itself goes, a digital thermal gun is almost a necessity to sample temp differences.
 
I do have a digital IR heat gun (see temp readings posted above).

Yes, I believe it's air flow too. This trans cooler is only 8" x 11".

I was told my by mechanic who helped me that he put the ports at the top to minimize drain-back into the trans, to minimize venting out again. So sideways or on the bottom with the ports is better? I also have this mounted on the driver's side, which is the same side as both rad hoses. Maybe I should move it to the passenger side and down so the bottom of the trans cooler is even with the bottom of the rad. Also thinking about putting the internal rad trans cooler back in series.

The first thing I would do is to temporarily remove the trans cooler from in front of the rad, twin the hoses temporarily and see if there is a noticeable difference in cooling. You're not going to toast your tranny for 10 minutes running. I'm not a fan of how you installed the trans cooler - it seems to be blocking a large area of air flow over the rad. Also, any heat generated by the trans moves vertically up the cooler ( the hottest point being at the top exactly where the hot coolant dumps in the upper tank ) which will happen with your installation. I prefer a cross flow trans cooler, say in the range of 5 x 18 mounted at least 2 inches in front of the rad and mounted horizontally. You don't need a gigantic cooler for a tranny - remember the cooling tube inside the rad doesn't have a large surface area and they worked just fine. One of the best coolers, and most popular, come off F150's out of the junk yards. Their compact, efficient, easy to mount and stack plated on the end manifolds. You can't imagine the heat you can generate in a truck tranny under load. Try clearing obstructions from the front of the rad and I think you'll see a dramatic change in cooling. Even a small 3 1/2 by 16 cooler will mount in a slanted orientation just in front of the cross member under and behind the front bumper yielding great cooling when moving and radiant off loading when standing still. As far as the performance of the cooling system itself goes, a digital thermal gun is almost a necessity to sample temp differences.

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One other thing - at idle after warm up with no driving, the temp is about 200F.
After backing up and moving forward only 100 yards, the temp shoots up to 220-225F and stays there whether moving or at idle.
 
Hmmmm, It is possible, just for grins...to take that external Trans cooler and route the output back thru the RAD, in effect putting the 2 in series? I know it's not what you wanted to hear, but if the RAD has dead space anyway, I don't see how it could hurt.

Example: Out of the Trans to the external cooler, then the output of the external cooler is then routed back into the RAD, then the output of the Radiator goes back to the Transmission. Hell, It's just a spit-balling idea.


Yes. That's how I have mine set up. Oil to rad then to cooler.
 
I do have a digital IR heat gun (see temp readings posted above).

Yes, I believe it's air flow too. This trans cooler is only 8" x 11".

I was told my by mechanic who helped me that he put the ports at the top to minimize drain-back into the trans, to minimize venting out again. So sideways or on the bottom with the ports is better? I also have this mounted on the driver's side, which is the same side as both rad hoses. Maybe I should move it to the passenger side and down so the bottom of the trans cooler is even with the bottom of the rad. Also thinking about putting the internal rad trans cooler back in series.

Depends on the cooler. My B&M cooler had specific instructions on how to mount it. They recommended side mounting but input being on top of the cooler and output on the bottom, IIRC. This allows a bypass feature for when the trans fluid is too cold. Yours may have different internal config.
 
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