So pretty sure I dickered something up with my carburetor. After a couple of past weekends getting quality of life improvements done, things where looking up. I had heat and functioning controls, new thermostat since there was none when I removed the housing, window channel kit and weather stripping finally cut out all the wind rushing noise in the cab, new striker bolts (dennis carpenter has the correct bushing size where doorman's where too big) making the door not rattle around. Then to close the book so to speak, I messed with the idle screws on the carb without fully understanding what I was doing. I was just wanting a lower idle than the 1300 rpm it would normally run.

Turing the two idle mixture screws on either side of the pcv port (only know things because I have since been reading a manual) and noticed rpm going up or down depending on direction I was turning. So plugged in my timing light with an rpm readout and was getting down to ~750 rpm. I was turning the screws a lot before I realized the other screw next to the throttle cable should be moving instead. I put the other two screws back to where they were (I am thinking I missed the mark) and backed out the idle speed screw till I saw 750ish rpm and happy to hear the engine run just fine. The engine was good a warmed up already since getting back from 30min drive around town. I Left it at that and called it a night.

Next day I go to return a rented tool and get some groceries and I noticed on my down down the highway the temp was getting pretty high (lot higher than normal). Got to the parts store and was steaming a bit from the valve covers. I checked my oil and was dangerously low so dropped some in to bring it up to the mark and headed to my next stop watching the temp gauge. At first it was coming down fairly good but didn't last long as it was climbing back up. Got to the store and was steaming a lot more than at the parts store. Checked my oil and was still there at the mark. Felt the top radiator hose and was good and hot, the overflow tank level was the same, felt the bottom radiator hose and was not all that hot, pretty warm but not hot. Go into the store to shop and let Dan cool down.

Heading my way home quick as I could (only couple miles between each stop and home) watching the gauge slowly climbing. Flying down our gravel road and heard the motor start to do that ping/knock sound so I killed it and coasted around to the barn. Same old steam spewing from the valve covers.

Time to sit down and RTFM to see what I messed up. I have an Edelbrock 1406 so there are a lot of resources luckily. Been a whole week and a half of driving since doing my radiator flush and that new thermostat. Seems like too much of a coincidence that messing with the fuel mixture and have it not be the cause. I feel like I leaned the crap out of it and cooling system can't keep up.

 

Well, some days I feel like I'm a dinosaur but that doesn't actually make me one. Beware of troubleshooting based on what you feel. Troubleshoot based on what you actually have in front of you. Sounds like the truck was running okay (other than the apparent overheating) after your carb adjustments. With our lovely cool fall weather, the engine just loafing, and a massive radiator designed to cool that humongous engine during the harshest conditions, it's hard to imagine overheating caused by a lean condition.

I highly suspect you will find your radiator plugged with all the crap you loosened during the recent flushes. It's easy enough to check. With the engine running, point your handy infrared thermometer at the radiator inlet and record the temperature. Now measure the temperature at the radiator outlet. If the radiator is properly transferring heat to the atmosphere, you should see at least a 30 degree drop. Take both readings on the metal, not the rubber hose, for the most accuracy.

The other possibility is your new thermostat has failed. Once again, measure the temperature at the radiator inlet or the thermostat housing. I've had several new thermostats bad right from the box. I've reached the point that I won't install one until I test it for accuracy in a pot of boiling water.

 

Just put a new battery in my thermometer too! I will run that test to see what I get. I don't have my shroud installed yet so I fear I won't get much of a temperature difference idling in the barn. Planned on keeping today as my couch potato day but might have to mess with getting the shroud on too.

I finished the manual with the card tuning and adjustment to I will get that to where it should be too.

I really hate coincidences. The last thing you touched should be what messed it up.

 

Since the idle mixture screws only adjust fuel mixture at idle, and off idle fuel mixture is a function of the main jets, I doubt overheating was caused by any carb adjustments. Next time, before making carb adjustments clean and lube the choke flap pivot points, springs, and linkages first. Making adjustments to compensate for a sticky dirty choke is the path to madness.

Debris may may have lodged / blocked the t-stat passage?

 

Is there any chance that you put the thermostat in backwards, not having the original to look at? The 'spring side' of the stat should face the engine.

 

Seems more likely. I'll test the thermostat in a pot of water on the stove.


Thermostat is in properly. Been driving for the past week and a half with the temps behaving like the should since my radiator flush.

I'll poke my head into it and focus on the cooling system. Maybe a slower RPM got the water pump to dislodge something due to it spinning slower than it usually would.

 

This the thermostat as I pulled it out; stuck open...

Bummed to find more brown color water in there (haven't added antifreeze just yet). Maybe I am looking at a clogged radiator?

I assume if I leave the thermostat out and run the motor and see water flowing through the open cap, radiator is good?

 

Wow, but not what you'd expect to find when investigating an overheat.

In theory, overheating can be caused by too much coolant flow, such as if the thermostat was removed. Coolant then flows too quickly through the radiator, and doesn't have time to transfer heat to the atmosphere. But would a thermostat stuck open cause this? I don't think so, because it still acts as a restrictor.

Even though you've found one fault, I think the root cause lies elsewhere. Fix what you've found so far and keep investigating. I wouldn't bother trying anything without a thermostat. Put the truck back to the correct configuration (thermostat installed) and keep going.

You've already had one thermostat bad from stock, or nearly so. Try a different brand, preferably a name brand, not the house brand from a discount chain. Test it before installation, too.

 

So found out the brand I got is called Fail Safe. It will lock open to keep water flowing. looking at it more I do see the tabs that engage to keep it open. Not sure at what temp it does this though. I put a 195 in there.

Got a new one (same brand) and will stick it in there and look for flow in the radiator and measure temps off of the inlet and outlet.

 

Interesting. Never heard of one until now. Me not knowing something? Who'd have thunk?

https://motorad.com/products/fail-safe-thermostats/


According to the manufacturer, there's a backup sensing mechanism that locks open if the coolant temperature gets too high. Once locked open, you must replace it. Nice protective feature, but might get kind of spendy during troubleshooting.

 

If it overheats sitting around town and idling, you have a air flow problem. Your missing shroud can cause this. If it heats up driving down the road, you have a coolant flow problem. What does your radiator look like inside? If it has a bunch of white crusty stuff in it, I bet it's clogged.

 

I was doing 70mph on the highway watching the needle climbing. So flow issue sounds about right.

I'll get a video of my tests. I did like 9 flushes of water till I was seeing clear water draining out of the radiator and flowing through the tubes at the top when you have the cap off. So for the last week and a half things where peachy, did about ~100 miles. After I messed with the idle speed bringing it down, the water pump would spin slower, possibly the right conditions for something coming loose or air pocket?

 

With the thermostat missing, this suggests the previous owner also had overheating issues. Removing the thermostat was his likely "fix".

Radiator flushes? Never had much confidence in the home version. They're fine as preventive maintenance. But if trying to cure overheating, it's usually too late. Even if some crud flushes out, there's plenty more left behind. That crud is caked inside and isn't going to budge for a garden hose. The radiator will typically need a professional hot tank treatment with some powerful chemicals, followed by flow testing to be sure all of the passages are clear.

Not trying to burst your bubble, but trying to prepare you for what to expect if troubleshooting points to a clogged radiator.

Also, make sure the lower radiator hose has the spiral wire inside. With the system cold, remove the cap and try to squeeze the lower hose. If the wire is missing or broken, you'll be able to squeeze the hose shut. Since this is the return hose, it will collapse under suction if the radiator is partially restricted. This blocks coolant flow, but the hose returns to normal when you shut off the engine and open the hood for a looksee.

 

Turn for the worse. I ran the truck after testing the thermostat (opens up right at 195) and installing it. Radiator looked bone dry so added water and waited for the thermostat to open. About 15 mins in, the thermometer was only reading like 75 degrees. By that time I see the steam coming up again so I shut it off. Next I hear dripping from under the truck. Take a looksee and sure enough, it's nearly puking. Crawled under to see if I can locate the source but lost it by the motor mount and headers. Couldn't see anything from the top side either.

So this going to be a head gasket or freeze plug? Next test a compression test?

I know that the lower hose does not have a wire in it as I was pulling it part of the flushing ritual. The radiator was not clogged at that time. Something happened from about 5pm on a Saturday when I left the truck till about 12pm on Sunday when I went out for an errand.

Gotta find that other leak and plug that before I can get back to testing the radiator for flow I am assuming.

 

It sounds like a core plug (freeze plug) is leaking as that is the only think I can think would be by the motor mount area.

As was pointed out you can flush everything and still have issues.
You need to have the radiator flow tested to see if it is any good.
There could be mud sitting at the bottom of the block. This mud insulates from heat being pulled from the motor to the coolant.

I have a motor that has about 64K on it that this is an issue with. I sure sign also is most of the core plugs have rusted even 1 in the head and they don't normally rust out.

When you change out that plug, do them all, feel inside the block for mud sitting there. May want to take wire and fish it inside to break up the mud and flush before putting the plugs back in.
Dave ----