I have a NT 37 with a similar engine (have an aftercooler as well). I use a refractor I bought off Amazon. I check specific gravity on my lead acid battery bank (6 golf carts) and to check coolant. It seems reasonably well made, and is accurate enough for my purposes. I have cross checked it on the batteries. As stated by others just treat it carefully, probably not as well built as the Fleetguard, but I could buy about 7 replacements for the cost of the Fleetguard. On Amazon, check out reviews, recommendations (all with a grain of salt) and you should do fine.