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Throttle Body Coolant Bypass... Results Inside.

Old 09-29-2018, 01:29 AM
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Default Throttle Body Coolant Bypass... Results Inside.

Everybody does this modification citing it cooling IATs which I agreed with 100%. However, I had never seen how effective the modification really is so I set out to measure it's success myself in the best "bro science" way I possibly could.

Here's what I found when I did the throttle body coolant bypass on my 2000 WS6... I took multiple measurements with an infrared thermometer before and after installing a TB bypass kit. I drove the same route on the same day, the same way to measure the changes. A video outlining this is below.


Here is a spreadsheet I put together of the effectiveness of the bypass kits. They all work the same (I'm sure), and in principal should yield similar results. This was done on a 40ish degree day in Minnesota. The "IR TB Temps" were taken with an IR thermometer by averaging two readings. One on the drivers side of the TB, and one on the passengers side.



There was quite a difference considering the throttle body in theory should have continued to get warmer if thermal heat soak was going to make a large impact. I suspect the coolant was largely responsible for the initial temperature climb, and subsequent temperature decline. You be the judge!!!!

We all knew this was a good mod to do, but here is "how good".

Last edited by bjohn; 09-29-2018 at 11:54 AM.
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Old 09-29-2018, 09:14 AM
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The pic you posted shows 75.35 on the 24 mile trip after the bypass, but the video said 73.35.
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Old 09-29-2018, 11:15 AM
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It appears that doing this had a huge stabilizing effect on temps, which is a GOOD thing!
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Old 09-29-2018, 11:57 AM
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Originally Posted by BTC View Post
The pic you posted shows 75.35 on the 24 mile trip after the bypass, but the video said 73.35.
You would be correct, there was a discrepancy there! I was actually wrong when I went back and checked my math. I must have totally fat fingered that one haha. I updated the temp chart to reflect the change! Thanks for catching it.

Originally Posted by G Atsma View Post
It appears that doing this had a huge stabilizing effect on temps, which is a GOOD thing!
That's what I saw too. There was a dramatic ramp up in temperature with the coolant hoses connected (shocker). Without them it was noticeably cooler (shocker again lol).

The point if it was to try and gauge what effect the coolant hoses really had on the TB temps.
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Old 09-29-2018, 01:36 PM
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Thank you for doing a well documented, back to back test under the same conditions. :-)
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Old 10-06-2018, 12:08 PM
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Originally Posted by Chris Paveglio View Post
Thank you for doing a well documented, back to back test under the same conditions. :-)
Thanks for the feedback! It was ballpark science but I think the point I was trying to convey came across fairly accurately lol. We all knew the throttle body would cool off without coolant running through it, but nobody could quantify how much.

I would be interested to see a before and after of IAT's. Unfortunately, I'm not equipped to do something like that at this time. I'd suspect it's not a massive difference, but maybe a degree or two?.... Hard to say without testing it haha.





QUESTION!!!!

Someone had commented on the YouTube video that another reason the engineers run coolant through the throttle body was to aid in preventing carbon build up. I can't find that information anywhere. Is that a thing or not?... Shouldn't be a problem with an aftermarket lid and the EGR being deleted. But in an OEM setup, is that part of the reasoning?
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Old 10-06-2018, 12:14 PM
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I could see carbon building up if there was actually combustion happening close by (lol), but from EGR? Only the earliest LS engines had that, and not sure how stabilizing the temp of the TB would affect that.
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Old 10-06-2018, 11:09 PM
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fairly sure the coolant passage is so the throttle body wouldn't freeze up in case the car was ever driven in Antarctica.

smurfing GM.
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Old 10-07-2018, 08:02 AM
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Nice research, thank you for sharing OP.

The coolant was routed to the throttle body to prevent it is in hp or freezing. 200-220 degree coolant isn't going keep the TB hot enough to burn off carbon build up or prevent it. My stock 245,000 mile 02 Z28 is proof of that

Last edited by 99 Black Bird T/A; 10-07-2018 at 08:23 AM.
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Old 10-07-2018, 05:01 PM
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Originally Posted by G Atsma View Post
I could see carbon building up if there was actually combustion happening close by (lol), but from EGR? Only the earliest LS engines had that, and not sure how stabilizing the temp of the TB would affect that.
I agree with carbon buildup only being near an area of combustion. Not sure what might cause it on a throttle body, but the guy was somewhat adamant about it being a big reason to keep it.

Originally Posted by dreadpirateroberts View Post
fairly sure the coolant passage is so the throttle body wouldn't freeze up in case the car was ever driven in Antarctica.

smurfing GM.
That was my understanding too lol. There's what, a zero percent chance of these things being driven below 0*F?.....

Originally Posted by 99 Black Bird T/A View Post
Nice research, thank you for sharing OP.

The coolant was routed to the throttle body to prevent it is in hp or freezing. 200-220 degree coolant isn't going keep the TB hot enough to burn off carbon build up or prevent it. My stock 245,000 mile 02 Z28 is proof of that
Thanks, hope it was somewhat informative haha. I'm sort of relieved that nobody else has heard of the "carbon buildup" aspect of it on here. Couldn't find any information searching for it.

Good on you for racking up 245k miles haha! Some people think that these cars should be parted out if someone drives them a lot.
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Old 10-07-2018, 05:51 PM
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What cam is in that car? Just curious
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Old 10-08-2018, 09:10 PM
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It's a Brian Tooley Racing Stage 4 Cam.
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Old 10-09-2018, 12:25 PM
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Nice effort and interesting results!

As noted above, the sole purpose of routing coolant through the throttle body is to improve operational characteristics in cold-weather conditions. Essentially, that's accomplished by keeping fuel atomized for efficient combustion, which also limits emissions at idle and low-speed during closed-loop operation.

I'd be curious to see if the reduction associated with the throttle body bypass had any real effect on full-throttle performance. I'm guessing that airflow passes through the throttle body so quickly at high rpm that it has little time to absorb a significant amount of coolant heat. Has anyone ever back-to-back tested this on a dyno?
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Old 10-09-2018, 02:01 PM
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I'm pretty sure someone tested this long ago, and it was good for ~ 6hp under heat soaked conditions, but that may have been on the LT1.
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Old 10-09-2018, 02:49 PM
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This thread has a very small before and after dyno graph. It appears to be for an LT1 and I have no idea how trustworthy it might be.
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Old 10-09-2018, 03:51 PM
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Freeze-up is actually most likely to be a problem when it's just above freezing and very humid, like, foggy. Aircraft carbs do it from flying through clouds, which are often about those conditions.

A 2% HP difference seems believable.
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Old 10-10-2018, 04:03 PM
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Good thread, agree there is no reason not to do this mod.

For carbon buildup just take off the TB and clean it once in a while. I do that anyway since there is always some junk around the edge of the blade and in the IAC hole.
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Old 10-11-2018, 09:21 PM
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Originally Posted by RB04Av View Post
Freeze-up is actually most likely to be a problem when it's just above freezing and very humid, like, foggy. Aircraft carbs do it from flying through clouds, which are often about those conditions.

A 2% HP difference seems believable.
Interesting point. I can see something like that happening if there was a LOT of consistent air flow going through the throttle body for a long period of time. Makes me wonder why it never seems to actually be an issue in passenger vehicles... Especially vehicles that never came with this from the factory.

Originally Posted by infinitebird View Post
Good thread, agree there is no reason not to do this mod.

For carbon buildup just take off the TB and clean it once in a while. I do that anyway since there is always some junk around the edge of the blade and in the IAC hole.
I agree with you. I'd rather clean it that deal with "possible" contamination on the TB lol
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Old 10-13-2018, 12:09 AM
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I did it on my 01 T/A and afterward I had a couple of rough running episodes after start up when the car had been parked outside on very cold days.
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Old 10-13-2018, 09:18 PM
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wonder why it never seems to actually be an issue in passenger vehicles
Because they don't very often fly through clouds at a few thousand feet above the Earth's surface at temps in the low 30s for long periods of time at a stretch... although some do.

Get a bit of that kind of experience and you'll understand better why the factory did what they did. Not saying it's "right", you "shouldn't undo it", or anything of the kind; just, UNDERSTAND what you're doing/undoing, and what the factory's intentions were, and that will help you make an informed decision one way or the other. The factory guys/gals aren't STUPID (much... often...) but the reasons they do things the way they did are not always obvious to the casual observer. Sometimes "max power" isn't the ONLY consideration. Especially at altitude.
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