How I cooled my IMA battery without using a leaf blower

Last update:   9/10/2019  (minor corrections)  Return to Insight home page


If you live in a warm area of the country and or drive in traffic a lot you may have heard your IMA battery cooling fan running if you listened carefully at a stop light.  If you have an OBDIIc&c gage you can set it to read the IMA battery temperature (and many other data points of the G1 Insight.)

In South Florida we are used to seeing Summer temperatures in the 95+F range.  In AZ that would be a cool day!  Even with the A/C ON my battery temperature would rise to 105F before the cooling fan finally ran at high speed.  I would like my battery temperature remain below 93 F if possible.  When I first got my car I checked around the IPU case and realized that the warm air in the case was expected to exit the case out the bottom even if the fan wasn't running!

The last I heard warm air rises.  (Think hot air balloon.)  So in affect until the fan was running the warm air around the battery just stayed in the IPU.  i.e. No real natural air convection at all.  The case can radiate a small amount of the heat but that really doesn't cool the core of the battery enough to matter.

I checked around the black flexible insert storage bin in the "trunk" under the hatch trap door and it seemed to be blocking a lot of the air flow from the bottom of the tire well to wherever it was expected to leave the tire well.  I permanently removed the liner which also gives me a little more storage space.

I bought my car in December 2013.  So for a few months the battery temperature wasn't really a problem.  Once it got warmer, and after I bought an OBDIIc&c, I could see the battery was running rather warm for my taste.  I drove through the first Summer to get a base line of what temperature the battery ran at under various conditions.

Members of the  have discussed this several times in the past and some members tried using a more powerful battery cooling fan.  In most case this helped but they reported that the fan sounded like a leaf blower when running.

This article is to present what I've found in regard to where the warm air from the IPU was designed to go and how I improved the air flow without using a leaf blower.  The modifications I did are rather simple and have reduced my battery temperature while still using the original Insight fan.  The normal high temperature I've seen with these mods is ~91 to 95F and the cooling fan only runs after a lot of stop and go traffic since the I did the changes.  (I sometimes do long term tests to make sure changes really work as intended.)

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To see an enlarged view of most pictures, click on the picture or right click and select "View Image".

Have you ever wondered how the warm air is supposed to get out of the tire well?
stock looking mods done already

This picture shows the right side rear ventilation grill at the rear of the Insight  and the small metal panel that has to be removed when you open the IPU box.  You don't have to open the box for my mods.  You will modify this piece of metal to allow more air flow from the tire well.  This will be explained in the following pictures.

right side air flow

The sheet metal panel shown in the picture to the left has been removed to be modified and to show the air flow from the IPU box and out of the tire well.  The vertical grill wall is spaced away from the body of the car.  (Actually the sheet metal in the left picture has already been modified but the modification isn't visible if done properly.)

hand behind vent

As you can see in this view there is a lot of room for the warm air to get behind the grill panel IF the stock sheet metal wasn't blocking a good bit of the area where my hand is located.

In affect the warm air is blown out the bottom of the IPU case and travels upward behind the paneling that the grill is mounted on.  The warm air can then either go through the vent into the cabin of the car or out the back of the car.  Behind each left and right rear grill there is a rather large hole that eventually leads to the rear flapper vents at the back of the car.

There are two rectangular air vents to the outside world located on either side of the rear of car.  These vents have a series of soft flexible flappers that open by the air flowing through the cabin into the rear grill vents.  The rear vents also make it easier to close the doors with the windows and hatch shut.

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stock sheet metal marked for cutting

This is the stock piece of sheet metal before cutting.  The red line is where the metal is cut to remove the area above the line. Ignore the drilled series of holes above the red line which I did in a failed attempt to increase the air flow.

Before doing anything to remove the sheet metal panel, mark the edge of the horizontal part of the vertical grill panel where it rests on the metal. Or even quicker, just place a strip of masking tape on the metal along that edge.  This is just a reference point to actually marking the cut line.

Next remove the metal and measure the bottom width of the horizontal part of the grill wall panel where it normally sits on the metal.  Use the width dimension to place a second mark above the tape or pencil line on the sheet metal.  The 2nd line is the red cut line. Cut the panel and file the edge smooth and reinstall the metal piece.

Now that the hard part is over, here's how to modify the left side of the car.

stock left side foam

Unlike the right side vent system, the stock left side grill only allows cabin air to exit the cabin through the left rear flapper valve.  The forward end of the foam also blocks any air flow from the left side of the IPU case.

All you need to do this mod is a sharp knife.

left foam partially removed

To remove the foam block, first move the gray cosmetic material away from the left side of the foam block.  Grasp the left end (towards the rear of the car) of the foam and work it towards the center of the car. Eventually it will come loose and you can then move it towards the rear of the car to disengage it from the side of the IPU.

left side modified air flow

This is the air flow of the modified foam.  There is also some air flow from the left side of the IPU from a passageway similar to the one on the right side of the IPU.

The messy left side hole is a mistake on my part using a hack saw blade. Make your cuts nice and straight with a sharp knife.

show cut out areas

Extend the height of the cutouts higher than shown above.  The inside and outside heights of the foam are not the same so take that into account when making the top of cutouts.

I wouldn't try to make the cutouts huge because you still need the strength of the foam in case you place some heavy objects on top of it later.

front end of foam cutouts

This view is the front end of the foam block.  These holes are to allow air flow around the left side of the IPU case.

tool I use to remove the round plastic gizmos

This is the tool I use to pop the round head plastic "rivets" that are used around the car.  It is a garden tool used to cut the roots of weeds etc.

A few final hints that might help

  1. If you ever have to open the IPU case use some flexible RTV or silicone caulking to seal the gaps around the IMA battery cooling fan.
  2. If you live in a really hot area of the country, consider cutting a rectangular slot/hole along the top side wall of the IPU case.  This should allow some convection cooling of the case.  Best to cover the hole with a screen to keep mice etc out of the IPU.  The side of the case is not smooth; it has all sorts of high and low areas.  This will make cutting a slot a PITA.
  3. I would not leave the flexible "trunk" in the car.  From what I can tell it seems to seal the bottom of the IPU case so the warm air is very restricted to leave the area.  There is a gap around the bottom of the IPU case which would allow some air to get out of the case into the passageways on the left and right (& front?) sides of the case.  That is why I went to so much trouble in utilizing the side passageways.
  4. NEVER place soft material in the "trunk" so that it blocks air flow from the bottom of the IPU case or the right side foam cutouts.
  5. Don't use a hacksaw blade to cut the holes in the foam.  It will tear small globs of the foam loose and not give a smooth edge.  The result is the messy looking "holes" in my left side cutout.

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