Can an aftermarket bumper cause excessive transmission temps?

[Option01]

Hello, I'm wondering if anyone with an aftermarket bumper has experienced high transmission temps due to the bumper blocking airflow?

I recently had a steel bumper installed on my 4Runner and subsequently noticed my cupholders in the center console getting hot after long drives. I took it in to a shop and they couldn't find anything wrong mechanically but suggested that it might be due to the new bumper blocking airflow to the lower section of the radiator. (I'm guessing the transmission cooling section is isolated to that region of the radiator?)

I bought a bluetooth OBDII scanner to monitor the transmission temps for myself and finally had a chance to try it out yesterday via a 1.5 hour drive into the mountains. It was mostly freeway driving with speeds around 60-65 mph with outside temps in the mid 80's. I left OD on since I was staying in 4th gear most of the time. It was only my wife and I in the vehicle with no additional weight or towing load. I do have 33" tires, roof rack, aftermarket bumper and a 4.88 re-gear.

Temps got up to 190 fairly quickly and remained there for a while until we started traveling at an incline where temps started increasing again. From there it was in the 220-240 range most of the time with one downshift spike going to 260.

I plan to install an additional cooler in series with the radiator but I hear those only take off around 20 degrees so I suspect I'll also need to modify the bumper to add some airflow to the lower radiator section as well. Before I go too far down that road though, I was wondering if anyone else with an aftermarket bumper had experienced anything similar and if so, did adding some airflow down low help?

 

[shadow247]

That entire lower half of the bumper is blocking the lower half of the radiator. I would think that could cause some issues. How is your coolant temp? The needle gauge can be way off from the OBD temp. I bet you are over 190 on your coolant temp. I sit right at 189 degrees all day long with my stock bumper.

 

[Option01]

That entire lower half of the bumper is blocking the lower half of the radiator. I would think that could cause some issues. How is your coolant temp? The needle gauge can be way off from the OBD temp. I bet you are over 190 on your coolant temp. I sit right at 189 degrees all day long with my stock bumper.

That's good to know, thank you! I'll be taking the 4runner back out on Friday so I'll also monitor the coolant temp and report back.

 

[phattyduck]

The stock trans cooler will keep the temps under 200*F much of the time (though it can't keep up if you are putting down some power with the torque converter unlocked). I'd suspect a cooling issue - and seeing as how the whole front is blocked off, I'd suspect the bumper is part of it. Once you have those coolant temps, that will be the information needed - it could also now be showing your fan clutch is weak or some other similar issue too.

My trans cooler is up behind the upper grill for this exact reason though (best airflow given that I have a plate bumper on there). That said, there are still large holes down lower to allow airflow to the bottom half of the radiator.

-Charlie

 

[mtbtim]

The answer is yes. Aftermarket steel bumpers cover some of the air flow getting to the radiator.

To keep my trans temp in check on my heavilly modified 3rd Gen, I installed a Hayden 699 cooler and decided to bypass the stock cooler in the radiator.


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This is another video covering how to run a trans cooler in-series.

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[Option01]

The answer is yes. Aftermarket steel bumpers cover some of the air flow getting to the radiator.

To keep my trans temp in check on my heavilly modified 3rd Gen, I installed a Hayden 699 cooler and decided to bypass the stock cooler in the radiator.

Interesting. So the Hayden 699 is sufficient to keep your transmission cooled all on it's own? Do you run a temp sensor or use an OBDII connection to keep tabs on the temp? I'd be curious to know what kinds of temps you get under prolonged high-load scenarios.

 

[mtbtim]

Interesting. So the Hayden 699 is sufficient to keep your transmission cooled all on it's own? Do you run a temp sensor or use an OBDII connection to keep tabs on the temp? I'd be curious to know what kinds of temps you get under prolonged high-load scenarios.

Yes, it's sufficient as a stand-alone cooler, but I employ all the tricks of the trade to keep my trans temp in check too. I turn overdrive off when I'm climbing sustained hills. OD off doesn't help below the speed at which you maintain 3rd gear though, which is around 40-45 mph. Below that, it does nothing for you. I also use 4Lo for any sustained off-road climb. It doesn't even have to be steep, just sustained. Running in 4hi should mostly be used for faster flat fire road sections. This means I don't travel all that fast sometimes, like around 20-25 mph, but that's ok with me. The goal is to get to my next camping destination without a major mechanical failure like burning up my auto trans.

Oh, and YES, I monitor my trans temp. Everybody with an auto trans should. Ignorance isn't bliss. If you wait for the "Idiot Light" to illuminate on the dash, you've done damage to your trans. That light comes on at around 300 degrees, which means your trans fluid is torched and you've no doubt done some damage.


Here's some more videos on this subject:

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<iframe width="560" height="315" src="https://www.youtube.com/embed/fT_2szdKXRM?si=AvyHWdSEK0CXXipj" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" allowfullscreen></iframe>

 

[Romeo1]

The CFM is what does the work for heat rejection.

I never noticed it before, but since Tim's thread about temps recently, I've been paying more attention to the various steel bumper brands and how the airflow is addressed. They all seem to have less open area than factory visually. I'd be interesting to what the open areas actually measure out to on some of these bumpers.

 

[96RedRunner]

With the AOR plate bumper triple digit temps slow rolling auto trans I've seen 190* at times, like Tim said choose your gears.

 

[Option01]

Yes, it's sufficient as a stand-alone cooler, but I employ all the tricks of the trade to keep my trans temp in check too. I turn overdrive off when I'm climbing sustained hills. OD off doesn't help below the speed at which you maintain 3rd gear though, which is around 40-45 mph. Below that, it does nothing for you.

Thanks for the info! I know OD off won't do any good below 40-45mph but does it do any good at 60-65mph since the transmission sticks pretty consistently in 4th gear at those speeds? I've heard the reason "OD off" lowers temps is because it prevents frequent shifts between 3rd and 4th. I had the impression it was the shifting that caused the higher temps. Or is there something beneficial about holding 3rd gear compared to holding 4th?

 

[Option01]

The CFM is what does the work for heat rejection.

I never noticed it before, but since Tim's thread about temps recently, I've been paying more attention to the various steel bumper brands and how the airflow is addressed. They all seem to have less open area than factory visually. I'd be interesting to what the open areas actually measure out to on some of these bumpers.

I was thinking about that too but looking back at the stock bumper with the license plate in place, it doesn't look like there's that much open space for airflow. It's certainly better than what I have now but I'd still expect more considering the size of the radiator.

 

[Option01]

With the AOR plate bumper triple digit temps slow rolling auto trans I've seen 190* at times, like Tim said choose your gears.

Oh nice! Yeah there's definitely some good airflow on that bumper (even with the winch in place).

Do you also have an extra transmission cooler or are you staying below 190 with the stock transmission cooling?

 

[thezentree]

My biggest gripe with Coastal Offroad's bumper design is that it blocks half the radiator. It does a great job of keeping a good approach angle and it's an attractive design, but it's a big compromise in engine cooling. I struggle to keep mine at normal temps, and I cut some holes in the back of the bumper to try to get some more air through the bottom half of the radiator, and added a B&M aux trans cooler.

My engine coolant stays around 190, and the trans is usually around 163-176, but on long grades it'll spike to 210.

 

[Endlessblockades]

I solved my engine coolant issues (set the jiggle valve on a new TStat to 6 O'Clock along with a new radiator and cap) and my high transmission temps issue ( trans cooler, drain-n-fills, magnefine) while I still had a fatlip bumper.

After installing a TNF plate bumper, I saw no changes at all. I use an ultragauge to keep track of temps.

Edit -

Prior to the work I was seeing up to 212 engine and (shudder) a max trans temp of 249. Only once (that I know of). Work to fix that began immediately.

Now I see engine temps of 188.6 all day on the freeway and 194ish under max offroad strain in hot ambient temp (4Lo OD off)

The trans temps now are at 155 freeway to 190/200 in the max off road conditions above.

 

[Option01]

My biggest gripe with Coastal Offroad's bumper design is that it blocks half the radiator. It does a great job of keeping a good approach angle and it's an attractive design, but it's a big compromise in engine cooling. I struggle to keep mine at normal temps, and I cut some holes in the back of the bumper to try to get some more air through the bottom half of the radiator, and added a B&M aux trans cooler.

My engine coolant stays around 190, and the trans is usually around 163-176, but on long grades it'll spike to 210.

Thank you for the reply! So you have the same bumper and it sounds like you had some success adding some holes and an aux trans cooler. Do you know if the added trans cooler has made the majority of the difference or have the added holes in the bumper made a sizeable different as well?

 

[Option01]

I solved my engine coolant issues (set the jiggle valve on a new TStat to 6 O'Clock along with a new radiator and cap) and my high transmission temps issue ( trans cooler, drain-n-fills, magnefine) while I still had a fatlip bumper.

After installing a TNF plate bumper, I saw no changes at all. I use an ultragauge to keep track of temps.

Edit -

Prior to the work I was seeing up to 212 engine and (shudder) a max trans temp of 249. Only once (that I know of). Work to fix that began immediately.

Now I see engine temps of 188.6 all day on the freeway and 194ish under max offroad strain in hot ambient temp (4Lo OD off)

The trans temps now are at 155 freeway to 190/200 in the max off road conditions above.

Thank you for the detailed info!

It's interesting that you were seeing such high temps even with the stock bumper. I do have a new radiator/cap installed but maybe I should look into replacing the thermostat? I'll track the engine temps on the way up the mountain on Friday and that should shed some additional light on my situation.

Either way, it sounds like adding an aux transmission cooler is a no-brainer but it would be nice to isolate/fix any other issues that might be contributing to my high temps.

 

[thezentree]

Thank you for the reply! So you have the same bumper and it sounds like you had some success adding some holes and an aux trans cooler. Do you know if the added trans cooler has made the majority of the difference or have the added holes in the bumper made a sizeable different as well?

Probably the trans cooler made the most difference, but it's hard to really say. Get both!

My trans cooler is plumbed in-line with the OEM radiator trans cooler, for what it's worth.

 

[phattyduck]

Thanks for the info! I know OD off won't do any good below 40-45mph but does it do any good at 60-65mph since the transmission sticks pretty consistently in 4th gear at those speeds? I've heard the reason "OD off" lowers temps is because it prevents frequent shifts between 3rd and 4th. I had the impression it was the shifting that caused the higher temps. Or is there something beneficial about holding 3rd gear compared to holding 4th?

Its all about keeping the torque converter locked as much as possible. It will only lock in the top 'available' gear (generally, though sometimes it will lock 3rd with OD on in the right conditions). A slipping torque converter makes a lot of heat to reject in the cooler.

OD on will only lock the converter starting at around 50mph (stock gears/tires) and quickly unlock with throttle application. OD off will lock the converter at 45mph reliably and keep it locked under much higher loads. That's the difference. It will never lock in 1st or 2nd on A340 trans.

-Charlie

 

[Option01]

Its all about keeping the torque converter locked as much as possible. It will only lock in the top 'available' gear (generally, though sometimes it will lock 3rd with OD on in the right conditions). A slipping torque converter makes a lot of heat to reject in the cooler.

OD on will only lock the converter starting at around 50mph (stock gears/tires) and quickly unlock with throttle application. OD off will lock the converter at 45mph reliably and keep it locked under much higher loads. That's the difference. It will never lock in 1st or 2nd on A340 trans.

-Charlie

Thank you again for the detailed explanation. Can you tell me what is meant by a "slipping" torque converter? Are you saying that even if the transmission is staying in 4th, the torque converter may still not be fully locked causing it to generate more heat? My apologies if its a silly question but I don't know much about automatic transmissions.

 

[Option01]

Probably the trans cooler made the most difference, but it's hard to really say. Get both!

My trans cooler is plumbed in-line with the OEM radiator trans cooler, for what it's worth.

Haha! Yeah I probably will end up doing both but adding holes to the bumper is going to be messy since the bedliner coating was already applied. I asked my wielder friend who built the bumper for me and he says he can add holes behind the decorative slots in the front plate but he said it may not be pretty so I was hoping I might be able to avoid going that route by installing an aux trans cooler. But there's still a lot of radiator and AC condenser down there as well that could also use more airflow so I'll probably do it.