Keeping our Jeeps cool is always a concern, especially if we drive them in parades where the pace is slow and the temperature on the asphalt gets hot. BMorgil and I both had overheating issues. I had a thermostat stick in Ham’s ’48 and blow half the coolant out all over the engine compartment, past the hood junction and down the sides of the truck. What a mess! Bob’s baby, PeeJ, was having hot flashes during the 2019 Jeep Fest Parade.
In the truck, even after I replaced the thermostat – it always worried me when it warmed up. The temperature sensor is at the back end of the engine – and the thermostat is right up front where it gets all of the cool air as I started down the road. If I made a hot run didn’t let the truck sit and warm up for about 15-minutes, I would watch the temperature gauge crawl upwards. I have a 160-degree thermostat in the truck, and the gauge would run up to well over 185-degrees (on hot days close to 200-degrees) before the thermostat would open and cool things down. There was always that nagging worry; “Has it stuck again?” The other concern was that the cylinder head was a lot hotter at the #4 end than it was up at #1 – was that going to make it warp?
In the late summer of 2019 we did a lot of research on thermostats. What we discovered was interesting. When our Jeeps were new (in 1948 and 1953) a thermostat was fully open at its rated temperature. Modern thermostats tend to start to open at their rated temperature. I borrowed the Long Suffering Wife’s stove and her oven thermometers and did some experiments on the kitchen stove with boiling water. (I reassured her that I wasn’t going to hurt her nice stainless steel pot.) Sure enough, at 160-degrees, the modern thermostat was just starting to peek open and it didn’t get fully open until about 185-degrees, almost 25-degrtees above its nominal rating. No wonder the engine got hot and then cooled down. Even though it was “normal”, I still didn’t like it.
BMorgil did some research and from his racing experience, he suggested that I try a different thermostat, a Milodon 16400. He said he was going to put in PeeJ and I ordered one to go in the truck. I just got around to putting it in – and what a difference it makes! One difference, it has an air bleed port, you can fill the block from the radiator fill and not get an air lock from a hard closed thermostat.
But, the biggest difference is how that thermostat opens. I started with a garage test where I could keep an eye on things. As the engine warmed up, the temperature gauge crawled up to 160-degrees and just stopped. I felt the top radiator hose and the top of the radiator tank and they were getting warm. The thermostat was holding 160 without overshoot. I was working on the truck for a couple of days and I would run it just to check things out – same story every time – 160 and stop.
Today I got it out on the road. I made a “hot run”; start it and hit the road with no warm-up. I kept a very close eye on the temperature gauge. Even running down the road as hard as I usually do; (a breath taking 42 MPH) – it stayed right on 160. NO overshoot. NO “stuck thermostat anxiety”.
As Pelago (Ira) would have said: “HOOOOOORAYDINGDONG YEAH!!!”
I heartily second Doc Dana’s suggestion for a Milodon 16400 (160-degree) or a Milodon 16401 (180-degree) thermostat for your F-134. (I’m not sure if they fit the L-134). When you order one, get a couple of good Fel-Pro gaskets as well. Both are a bit more expensive that an auto parts box store made in China thermostat or gasket, but the peace of mind of knowing that the gasket won’t leak and that the needle on the temperature gauge is going to stop where it is supposed to be is well worth the extra cost.
Now I just need to change out that dripping, pizzling cheap plastic radiator drain plug with a real brass petcock – there is always just one more thing on an old Jeep!
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