I am currently remodeling, thus not flying, my Cruzer and am thinking of changing up to a lithium battery. Currently have battery mounted on engine side of firewall. Lithium batteries do not like high temps. Does anyone know what the engine compartment/firewall temperatures run in a Cruzer? I have a UL engine.



Views: 438

Reply to This

Replies to This Discussion

I have a UL engine and Lithium battery mounted on the engine side of the firewall for 15 months and 110 hours with no issues.  Can’t answer your question about the temps in that area, but I did have high oil temps last summer until I changed to the larger cooler this Spring when I did the condition annual.  I have the stol 750 and Roger (at Zenith) sold me the battery and didn’t say anything negative about mounting it there.

Spend a bit more and buy a lithium battery designed for aircraft with integrated health monitoring and under/over voltage control circuitry, and don’t worry about a given ambient temp. I chose EarthX for my 701 for these and other safety features. 

I would think it would not be too hard to setup a thermocouple in the engine compartment to monitor the temperature.

A lot multimeters come with thermocouple reading ability. You could temporarily mount a probe in the engine compartment, hook up the meter and do a test flight.

Another option is to get the temperature dot sticker that stick on from McMaster Carr. They come in various temperature ranges with 5 dots per sticker. Typically about $2/sticker when a temperature is reached, the dot changes from silver to black and stays black so you can land, shut down and then open the cowl and determine the max temperature that was reached inside the cowl, can stick directly on a battery case.


See link from David above, that is what he did. I am confident that the engine compartment temps are below EarthX max operating temps, however, lithium batteries last a lot longer when use is restricted to room temperature. Based on David’s temps I may relocate it to cabin side of firewall. Or if it turns out to be a major pain leave it where it is and deal with a shorter battery life.

Thank you all for your useful and prompt feedback,



I flew my EarthX on the engine side of the firewall without problems for quite some time. Later, however, I was "cleaning up" the firewall while re-routing a fuel line and decided to re-locate the battery to the cabin side of the firewall.  Fortunately, I was able to utilize the same mounting holes for the battery box, making the re-location quick and easy - now that's lucky!  ;>)



I talked to earth-X before mounting mine engine-side, they said I should be fine.

Another option is to build a blast box (a shroud with an air inlet) to ensure cool temps.


I put a thermocouple near the firewall of my 601XL to answer this very question and to act as a fire detector of sorts.  It is located about even with the top of the engine by the nose gear strut top.  I consistently see temperatures about 30 degrees above ambient temp during cruise flight.  Not sure how this would relate to the 750 Cruzer, but it is probably pretty close.

Dave G.


New from Zenith:

Zenith Planes For Sale 

Classified listing for buying or selling your Zenith building or flying related stuff...

Custom Instrument Panels
for your Zenith

Custom instrument panels are now available directly from Zenith Aircraft Company exclusively for Zenith builders and owners. Pre-cut panel, Dynon and Garmin avionics, and more.

Zenith Homecoming Tee:

Zenair Floats

Flying On Your Own Wings:
A Complete Guide to Understanding Light Airplane Design, by Chris Heintz

Builder & Pilot Supplies:

Aircraft Insurance:


West Coast USA:

Pro Builder Assistance:


Transition training:

Lavion Aero

K&S Aviation Services

Aircraft Spruce & Specialty for all your building and pilot supplies!

How to videos from HomebuiltHELP.com

Developed specifically for Zenith builders (by a builder) these videos on DVD are a great help in building your own kit plane by providing practical hands-on construction information. Visit HomebuiltHelp.com for the latest DVD titles.

© 2024   Created by Zenith.Aero.   Powered by

Badges  |  Report an Issue  |  Terms of Service