GPW Jeep Temerpature GaugeTackling the overheating Jeep – Part 1

After struggling with overheating issues last week, this week I dove into trying to diagnose what the issue might be, the thermostat, the coolant, the radiator, etc. Plus taking some temperature readings and a test run without a thermostat.

After a relatively cool overcast first half of the year, the heat has finally found its way to Southern California, meaning the radiators and thermostats will be working overtime!

This all started on the 4th of July, after a cool morning for the parade, I was worried about the jeep overheating on the drive home, where I would have to traverse some hills. The Jeep has always had an issue with overheating since the restoration, but I’ve been able to keep it mostly at bay by waiting for the cooler parts of the day to drive or trying to keep it in 1st gear anytime it heats up.

And it was just as I thought, on the drive home from the parade (covered in last week’s update) the Jeep overheated.

It was about 91 degrees and dry, and while I took a route that has the large hill I have to take split into smaller hills, it went up to 210/215 at one point. I was able to switch into 1st and cool it down a bit, but it got to the point that the system wouldn’t go below 198 degrees. This is all with a 160 degree thermostat in the Jeep.

And here you can see the thermostat from when I installed the original GPW thermostat elbow, it is one of the modern built ones that are set to 160 degrees F. So it should be fully open at 160 degrees. That’s not to say I don’t have a bad thermostat! But it all needs to be tested.

Now, in the last update I had a lot of people say to ‘flush the system!’ I’ve done that… THREE times. Once with this PEAK radiator cleaner & flush, twice with CLR. Plus several water flushes to follow that. So the system has been flushed. How do I know that’s helped?

Because after the first flush with the PEAK, this what the inside looked like. It really broke up all the gunk. Who knows when the block/radiator was last flushed before I got the Jeep.

Working hard to get the system cleaned and really flushing it, eventually, I got it to look like this. It’s remained that clean for some time. I know it’s not 100% clean, but at least in the radiator here it’s pretty clean.

Looking inside the block (at the thermostat elbow), it too made a difference, cleaning it out pretty well (before and after)

As for the radiator, I did several flushes manually of just it. Cleaned out all the gunk I could. That doesn’t mean that it’s not blocked somewhere in the core, however. I looked at quotes to get it dipped and recored… but that would cost upwards of $900-$1k. That’s not worth it, as there’s no guarantee that something else won’t go wrong with it after that fix. A brand new perfect replica (not aluminum) radiator is about $650ish. As much as I love originality, I have a line between wasting time and money, not to mention safety and premature wear, when it comes to things like this.

That being said, there are two pin-hole sized leaks on the radiator cap neck. Not big, and after an hour of driving/20 minutes of sitting post-drive, this is the amount it leaked. I can’t imagine that much pressure is being lost here.

So, I decided to take a look at the thermostat last weekend, and see if there were any tests I could do.

That would include making sure the coolant leaving the radiator was cooler than the coolant going in… a sure sign that the radiator is blocked.

To do that, I would need an infrared thermometer… which I picked up on Amazon. It’s just a simple gun, but not the cheapest one as I wanted something that I could trust.

So I waited on Saturday till it was hot out. Sadly, it wasn’t as hot as the 4th of July, topping out in the upper 80s. So I went out to do a drive with the thermostat in. The idea being I’d do the exact same route with no thermostat later or the next day, so I could compare the two temperature readings. To get started, I took a look at the jeep’s temperature in the garage. The engine was cool, even though it was warm out.

The infrared thermometer (let’s call it thermo so I don’t have to type that out each time) said the block was the ambient room temp of around 74 degrees.

The driveway was measuring a warm 111-118 degrees outside. Yikes.

Where I like has a few gradual hills around the area, so I knew those would be good to test. It was hot, but there was also a cooler breeze blowing.

It didn’t take long for the temp gauge to come to life. Keep in mind, this is with the 160 thermostat in still.

(forgive the blurry shots, it’s hard to drive and take photos). Very quickly the temp got up to 180, then 185. Each time it would pass by 180, I would come to a stop, switch to 1st gear, and it would go back down to 178-180.

After a couple of laps around the area, I went to the first hill. As you can see, it’s not that steep, but still makes the Jeep work.

Here’s a look from the top. Again, not a big hill, but you can hear the Jeep working going up it.

Sure enough, that started to spike the temp. 190 pretty fast. Creeping towards 200…

Each time, at the top of the hill, I would stop, switch to first, and cool it down. Eventually, this was the ‘normal’ when going back to first. It would spike up to 205/210, then go back down to 198. While that might seem normal on a hot day, keep in mind it was only 86ish degrees, a cool breeze blowing, only going to 1st and 2nd gear, and a max speed of 30mph. There’s no reason it should be jumping like that.

Staying in 1st gear for a long while, I would get it down to about 195ish. But it wanted to go higher. For a 160 thermostat, it shouldn’t be this high.

Coming back home into the garage, I shut off the Jeep and started to take some measurements of the coolant system. The temp of the metal tube taking the coolant to the radiator was 172 degrees.

Compared to the tube taking the coolant from the radiator to the water pump was 157 degrees, much cooler showing me that the radiator is (at least) partially working. I’m not sure how much difference there should be, but that’s about 14 degrees different at least.

Measuring the head next to the temperature gauge inlet to the head was a warm 198 degrees. Which was about right to what the temp gauge said (205 at the time). Of course, the gauge always creeps up when you stop the Jeep after a drive.

The water pump was 180 degrees.

I decided to test the copper inlet tube for the coolant on the radiator, that was a higher 182 temp.

On the driver’s side front of the head, it was a super hot 237. The front of the block is often higher than the rear I’ve been told.

The radiator to water pump tube was now at a 120 degrees.

The top of the radiator was 159. I tried to measure the temp across the front of the radiator, as some have said that if there’s a sudden drop in temp, that could be a blocked vein. But, that was inconclusive as the temp stayed mostly the same the whole way across, and I wasn’t sure if it was reading the fins, rather than the veins.

One thing I also wanted to check was the deflection of the fan belt, as if the fan was slipping, that could cause it to overheat. But the belt was pretty tight, with a proper .6-.75 deflection. I used a ruler as I pushed down on the belt to measure.

One thing I did notice was a large crack in the fan belt! Yikes! It was still holding pretty strong, but I will need to replace this asap. I have two GPW Ford fan belts coming in to replace it, and I’m using a temporary fan belt that was on the Jeep when I got it to replace this for the meantime.

Another thing I wanted to check was the spark plugs to see if I was running a bit too rich causing more heat, and in turn overheating the engine quicker. But, the burn pattern on the end of the WW2 Firestone F-40 spark plugs look pretty darn good.

So, with that test out of the way, it was time to remove the thermostat from the elbow! After unscrewing the bolts, I used my rubber hammer to break it free from the gasket/RTV seal and I pulled it off… and was met with one HECK of a surprise.

What in the heck?! That was literally my though as I looked inside the elbow and saw this. At first, I couldn’t figure out what the heck that is. An animal carcass? A blog of debris? And keep in mind, this was after I already removed some to try and figure out what it was. There was about twice as much in there.

Looking inside the other end of the elbow, whatever this was extended in there through the thermostat.

It took some work to get the thermostat out because of whatever this was. But I finally got it out. It appears like it’s some sort of rag. Not a blue shop rag (the paper towel style), nor a paper towel. It was something thicker. It didn’t want to rip up. I have no idea where it came from. Was it in the GPW head somewhere when I got it and put it on the block? Was in inside the block and my flushes finally dislodged it? One thing I know is that I’ve opened the thermostat elbow three times… during the first restoration, I did when I cleaned up the engine out of the Jeep. Then when I changed out the head gasket on the block, and then a third time when I replaced the post-war elbow with a wartime GPW elbow. In any of those three times, this rag/material was not present in the thermostat.

I managed to get all the material out, and it seemed like the thermostat was still okay. It still made a good seal and it snapped right back into place. So, let’s focus on this thermostat, which is the one commonly sold by just about all Jeep vendors out there.

How it works is there’s an outside disk (silver) that forms a wall for the moving coolant. There’s an inner traveling disk that, when the thermostat is cold, makes a seal with the main disk so no coolant can pass through. It’s highly recommended to drill a hole in the top disk so the system can ‘burp’ air.

Looking from the bottom, you can see that the large spring is pushing that inner disk so there’s no liquid able to pass through. And you can see from the gold arrow, it’s a 160 degree thermostat.

As the thermostat heats up, the spring expands, pulling the center rod with the center disk downward, breaking the seal and allowing the liquid to travel to the radiator. The reason behind this is so the engine can get up to an operating temperature (Jeep engines, if not most engines, work better at certain heated temperatures). So it allows the engine to get to reach that specific operating temperature (especially in colder climates) and then the cooling system will start to keep it at that level of heat.

So, how do you test that a thermostat works? Well, if you have a pot, some water, and a stove… you can boil it. You will need a thermometer in order to watch the temperature.

As the temp starts to reach the degrees listed on the thermostat, it should start to open. And by the listed temp, it should open completely. So, in this case, at 160 (shown here), it should be fully open. But, it’s not. It’s just starting to open.

It actually took till about 170/175 before it really started to open, which I could tell as the center disk was lower from this angle.

So here’s the difference between closed and open. Notice how the top brass done has lowered below the silver disk level, and the rod has lowered, raising up the thermostat body.

So at about 165 degrees, it looks like this with the thermostat only partially open.

At around 175 or 180 (it’s hard to tell), it’s fully open, shown here. Notice how much space is now between the disks and how much the rod is sticking out. So what does this mean? Well, it’s not fully opening at 160. It should be. So, does that mean it’s a bad thermostat and the cause for the overheating? No, I don’t think THIS is the main reason. But it doesn’t help anything.

To truly test if the thermostat is the problem, we need to test the system without one altogether. That should, in a hot climate, keep the Jeep cool without question. Since I live in SoCal where temps are not going to be freezing unless overnight for only a few days in a year, some people actually drive their Jeeps in SoCal with no thermostat at all. There’s a debate from many on if that’s efficient or not, since it makes the engine get to the proper operating temps a lot slower, BUT it keeps the engine cool and not close to overheating. At any rate, I went ahead and applied some RTV sealer (no gasket) so make it so the coolant doesn’t leak, but there is no thermostat in here.

I cleaned the adjoining surface on the head.

I hooked it all up, bolted the elbow down, and waited 20 hours to the next day so the RTV could set.

I waited till the hot part of the next day, but it was about 3 degrees cooler. So about 83 degrees. Still a dry heat, and a cool breeze blowing. It felt hot still. So I did the exact same drive I did the day before. I stayed in 1st or 2nd gear, and stayed below 30mph.

It didn’t take long for the temp to hit 140, which some people say (without a thermostat) their Jeep won’t go above. Mine started to creep up not long after.

After a few drives around the streets, it was already up to 165ish.

It kept creeping up to 180, but I found after switching to 1st gear and driving a bit, it would go back down to 175ish.

And it stayed between 175 and 182 the whole drive. It never went above that, even on the hills. So, after the drive was done, I headed back to the house and pulled into the garage to start taking temp measurements.

The block to radiator was about 179, not far off from the drive the day before with the thermostat.

The radiator to water pump was showing 152, which is about 5 degrees from how it was the previous day.

And measuring the radiator input neck, it was about 176 degrees. Just a few degrees from the other day.

Measuring inside the radiator floor, it was 134 degrees.

The water pump seemed to be a bit cooler than the day before with the thermostat. But only by 6 degrees.

Measuring the head forward of the distributor, it was 187ish.

And just behind it where a coolant jacket is, it dropped to 169. So that is working.

The elbow was a warm 199 degrees. Makes sense as that heated coolant and air is going through there and is probably the hottest for the system.

So, what does that all mean? Well, without a thermostat, it ran 2-6 degrees cooler when taking the measurements directly. While it wouldn’t go over 182ish on the temperature gauge, it still seemed to be running much hotter than it should have with no thermostat at all. But what does that mean? Well, it still seems to point to the radiator being the main issue here. Possibly a major blockage preventing the Jeep from cooling the coolant as much as it could.

But, we also learned that the thermostat isn’t working as good as it should… so I had several people I need to get one of these bellows style NOS thermostats from the 40s/50s. These are identical to the WW2 style, and are NOS from the 50s. It even lists 1939-1950 Jeep on the box. It claims to start opening much sooner than 160. So I have one on order that will arrive next week. I’ll document the installation and results once I get it.

The other option, which I don’t really want to do, is getting a new radiator. As mentioned, because the radiator would be near or above $1000 to recore, it’s just not worth it when a brand new exact replica (not aluminum, a proper brass/copper one) is just a bit more than half that. So I have some decisions to make. I want to try the bellows thermostat before I go about looking into dropping $650 for a new radiator. So we’ll see what happens in part 2 next week!
Till the next update…