Ham's 48: Keeping Our Cool

Rack up another win for Doc Dana!

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!

He told me the same thing Larry when I had mine all together and between that a "arm chopper off blade with spacers" and a high volume water pump she stays pretty cool, we will see come August in Toledo I am sure of that.

So interesting. I remember parts of this but am just getting around to asking. So my j series got an upgraded radiator. Temp tops out like you said, but then dips down. We were trying to sort it. I think we replaced the thermostat a final time and done with it. So it was not as detailed a solution. I stopped addressing it when it stopped getting too hot on the top end. It still dips though. What should my concern level be given the temp variation, many times per day? Exactly what should I be concerned about, that is, what else could breakdown in what order? Very cool to know the thermostat on one end and the other on the other end, as a cause, and the thermo opening as another cause. No clue how to figure that out on mine, yet, but its in the hopper for future sorting out

DANG, that is some good info! Thanks

Thanks for the "Bump" Larry!

Fit's them all, all Willys and Jeeps from 1941 to 1971. Truth be known it is the same thermostat part number used in 60's and 70's era Chevrolet's. That Milodon is a "High Flow". it has a big window in it that's for sure. Like we spoke of on the other thread, these little water pumps are pretty primitive. Restriction is not their friend.

Premium brand engines, (CAT for instance) use one or two thermostats for redundancy. Over the last 12 gears, we have implemented that when in doubt, change them out. Since the vehicles were going into combat in the desert, it was cheap insurance. The coolant was already dropped, so it only cost a small amount of labor. The down side was that the CAT supplied thermostat replacements were cheap Chinese made stats. The OEM stats were as well. It wasn't terribly unusual to have a new replacement stick too.

Moral of the story, buy good parts once.

Just FYI - the Milodon packaging does say "Made in USA".

Great info on this thermostat. I've noticed this on my CJ a few times. Where it really got my attention is with my 1988 Chevy truck with a 350 small block. I've had the truck for almost 30 years. On the first heat cycle after starting in the morning, the temp will run up to well over 200 degrees and then drop down to normal and stay there. I've changed thermostats several times, always with the same results. I'll have to see if Milodon has one for the small block. You guys are great!

Gotta love "Made in USA". They are high quality. Brass and Stainless Steel.

Same part numbers Cajun, those Milodon part numbers will fit that 88' just fine. 16400 and 16401.

Well, when I get back from this hitch at work, I'm gonna try one of these on my Chevy!

Keeping Our Cool - Revisited

In the last post on this I made the comment: "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!"

Well, it turns out the real brass petcocks have English threads on them and the replacement radiator for the truck has a 12mm metric thread for the drain plug. Who'd of thunk it?

Anyway, I found a different plastic drain plug that doesn't pizzle in every direction as you take out, but you can't do a partial drain like you could do if there was a petcock there.

Sometimes we settle for good enough and move on to the next project. Harupmh!

Thank you for creating an update and for sharing tips on how to do it.

Larry here is a plastic one with an outlet. https://www.summitracing.com/parts/rnb-61123

Or you could use an oil pan drain. There are a few people making these. https://www.ezoilchangevalve.com/sto...m-1.25%5D.html

Be aware there is a 12mm x 1.25 which is probably what you have or, there is a 12mm by 1.75.