[Centerline]

I posted this about a week ago and have made some changes but the problem still exists. Here's the setup.

Fresh 331 hemi (.030 over), SB Chevy water pump conversion, Mopar electronic ignition, large custom built (PRC) aluminum radiator (new 7 lb cap) running a fixed blade mechanical fan and shroud. The air flow is adiquate to hold a dollar bill against the air conditioning condenser so the fan and shroud are working properly. The engine has about 8.5 compression with a single Edelbrock 600 CFM carb and Isky muscle car cam.

Broke it in with no thermostat and 100% water. The engine ran fine and didn't get over 190 the entire time it was running (some 20 minutes).

Since then I installed a new 180 thermostat and changed to a 50/50 mix. The engine runs fine and takes several minutes to warm up. Once it reaches 180 however it slowly climes (over a period of 5 minutes or so) up to 220. That's where I shut it off.

I changed out the temperature sending unit (had a new one sent from the manufacturer) but that didn't solve the problem. What is puzzling is the engine does not seem to be getting that hot. I can hold on to the upper radiator hose and it barely feels warm however the intake near the thermostat is pretty warm to the touch (which I would expect). With the radiator cap off and the engine running at 220 degrees the coolant is not boiling either. Its a down flow radiator and the cap isn't located near the upper hose fitting so I can't see how much coolant is actually being circulated but I can see there is some movement.

Now here's the strange part. Once you shut it off (at 220) you would expect it to heat soak for a while before cooling off. After letting the engine sit for less than 5 minutes the temp gauge reads about 180 and when the engine is restarted it slowly works its way from 180 back up to 220 before I shut it off again. This doesn't make sense. I would expect the engine to be at or higher than 220 when being restarted especially after sitting for just a few minutes but its not. By the way this all happens sitting in the garage while the engine is idling.

Anyone out there have any ideas? Other than the possibility of a bad (brand new) thermostat, I'm stumped on this one.

Centerline

 

[Deuce]

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Possible air lock..........I always like to drill a small 1/16 hole in the thermostat too.........

I would buy another 180........

 

[Dizturbed One]

I think your water temp gauge is just messed up buddy.

It happened to my good friends duster.

Take it out and boil the sensor on the gauge. If it reads about 210 degrees when the water is boiling (depending on elevation) then it's ok. If not, then it's wrong.

Remember, the higher elevation you are, the lower the boiling point will be. While it's about 212 at sea level, if you're at 7 thousand feet it could be as low as 198 to 200.

 

[DoubleVision]

Centerline, I don`t know if I have the answers or not, but, I have seen new thermostats not open until upwards of 230, I had one that did this a few times before it started to cycle properly at 180.
I would replace the thermostat just to see what happens, since the hose isn`t that hot it would seem as if the thermostat isn`t opening. I had many overheating problems with my small block cutlass, I figured out never fill it up at the radiator with it running, fill it up with it off, start it and fill the coolant resivour, the burping system will take care of the rest, after I did this it never ran hot anymore, afterwards I added 2 bottles of redline water wetter, and now that winter is almost here it runs too cool,, I can`t win for loosing. go back over everything in your cooling system and I`m sure the problem will surface, but take care of the simpliest things first, as overlooking the slightest thing in the cooling system will make it run hot, I`m living proof.

 

[Ghetto Jet]

You can test the thermostat in a pot of water on the stove.

 

[Triaged]

On what you discribe it sounds like the motor is running at the right temp (around 180*) but they gage is reading wrong.

You are using an electrical sender right? (I assume so because you say you sent it back for another one...you can't detach a mechanical one).

Electrical senders must have a good ground. There is only 1 wire running to the sender. The sender grounds directly to what it is tightended into. If you used Teflon tape the sender will have a very poor ground. I am somewhat sure that most senders have the resistance go up with temp so what you are experinecing makes sence.

Pull it out, clean both male and female threads, and reinstall dry or with some liquid thread sealer.

 

[poncho62]

Since the problem didn't show up until you installed the thermostat, that's where I would lay the blame.

 

[Centerline]

Removed the thermostat and ran the engine for about 15 minutes. The temp eventually reached 160 degrees. Guess the brand new thermostat is bad. First one I've ever seen bad from the start.

Thanks for all the help guys. I'm off to the local Napa for a new one.

Centerline

 

[[email protected]]

Early hemis are famous for being easy to cool so I would blame the thermostat or temp gauge. From what you describe, the gauge is really suspect. If it were a faulty thermostat and the engine temp was really reaching that high, it would take a long time to cool down, Where is the temperature sender located in the engine? Stock hemis put it in one of the blocked off water holes in the rear of the intake manifold. Might be an air pocket there, but I doubt it.

 

[Centerline]

Early hemis are famous for being easy to cool so I would blame the thermostat or temp gauge. From what you describe, the gauge is really suspect. If it were a faulty thermostat and the engine temp was really reaching that high, it would take a long time to cool down, Where is the temperature sender located in the engine? Stock hemis put it in one of the blocked off water holes in the rear of the intake manifold. Might be an air pocket there, but I doubt it.

The sender is in the stock location (drivers side rear of the intake). The gage was the first thing I suspected as well. Talked to the manufacturer and he said if anything is wrong it would be the sender. He sent me a new one the correct size for the opening in the manifold so I no longer have to use an adapter.

When I removed the thermostat I noticed a huge difference in the circulation of the coolant in the radiator so I believe one of two things is happening. Either the thermostat was not opening far enough or the passage isn't large enough in the thermostat to allow enough water to pass through to keep the engine cool. The fact that it ran for so long without coming up to temp with the thermostat removed tells me the gage is probably OK (brand new gage and new sending unit) so logic points to the thermostat. I'll replace it in a day or so and we'll see if it does the same thing.

Centerline

 

[[email protected]]

Plop it in a pan of boiling water on the stove. That'll tell if it is working. They usually work or don't, no in-between.

 

[Centerline]

Plop it in a pan of boiling water on the stove. That'll tell if it is working. They usually work or don't, no in-between.

Did just that. It started to open at 180 but wasn't fully open till the water was almost boiling (around 200+). I am concerned about the size of the hole in the thermostat as well. At 1" It seems very small in relation to the size of the housing which is 3 1/2" and I'm not sure even if it was fully open it would allow enough water to get through. Think I'll try to find one that is a bit larger.

I'm going to hook up a mechanical temp gage and install a new thermostat and that should tell if it is the gauge for sure. I'm also going to back off a little on the timing to see if that helps. I am running it pretty advanced at the moment so we'll see.

Centerline

 

[4 Jaw Chuck]

I once had 4 bad thermostats in a row Centerline, from different stores and different mfg's too. I test them all now before installation, I keep the bad ones around so I can test them. I throw them all into a pot of water together and suspend them from a string, they are all marked with their opening point and full open point so I don't have to measure with a thermocouple anymore.

I even got one 195 stat for a 2.8 litre V6 Ford engine that doesn't start to open until after 212 F, I loved that one because I had to hitch into to town to get a replacement and then hitch back to the truck and replace it on the highway and then drive back to the store and replace it again in the parking lot.

Last time I trust "Tested and passed with pride by inspector #12".

 

[NAIRB]

Centerline,

I rebuilt a 350 Vortec engine about a month ago. I had the same problem. I had installed a brand new Gates thermostat, but the thing just kept getting hotter and hotter. The upper hose was cold.

I installed ANOTHER Gates thermostat and it did the same thing.

I then tried a different brand ( A Robertshaw Superstat) and it cooled right down. Faulty new parts seem to be more prevalent than they used to be.


Another trick I try when I have one giving me fits like this is to drill a very small "weep" hole into the thermostat, (maybe .100" orifice.", that seems to help alleviate air pockets and smooths out the temp range.

 

[[email protected]]

Did just that. It started to open at 180 but wasn't fully open till the water was almost boiling (around 200+). I am concerned about the size of the hole in the thermostat as well. At 1" It seems very small in relation to the size of the housing which is 3 1/2" and I'm not sure even if it was fully open it would allow enough water to get through. Think I'll try to find one that is a bit larger.

I'm going to hook up a mechanical temp gage and install a new thermostat and that should tell if it is the gauge for sure. I'm also going to back off a little on the timing to see if that helps. I am running it pretty advanced at the moment so we'll see.

Centerline

They sell a 'high performance' thermostat that opens almost the entire area. Find it on the same rack as the standard ones. That is what use in my hemi.

 

[TurboS10]

I would guess that the guage could also be an issue. I started noticing that my S-10 begain running very hot before this last tear down. It got to the point that the guage would read 300 degrees or so. First time I paniced untill I popped the hood and the water was not even boiling in the radiator hose or belching out water everywhere. My autogauge temp gauge obviously has problems. I think I must have damaged the line or something with too much twisting or something.

BTW, 220 is not that hot. If water is not boiling in the engine then it is just fine. You just have to keep it below boiling so that you dont get real hot spots and things get bad.

Chris

 

[Centerline]

...BTW, 220 is not that hot. If water is not boiling in the engine then it is just fine. You just have to keep it below boiling so that you dont get real hot spots and things get bad.

I agree that 220 isn't that hot for modern engines. With this being a 50 year old hunk of iron I don't want to take any chances. Especially since I've invested a good deal of money and effort to make sure the cooling system is more than adequate. I would expect this engine should run normally at 180. Maybe make it to 190 or 195 with the air on in hot weather.

The more testing I do the more I'm convinced its the thermostat. Probably a combination of too small a water passage and late opening. That said, I backed off on the timing to 8* initial and total of 38*@ 2500 rpm. Let it sit and idle for 25 minutes (no thermostat) and the temp finally reached about 185-190 but wouldn't go any higher. With a functioning thermostat it should run 10 or 15 degrees cooler since the thermostat will allow the coolant to stay in the radiator a little longer which will increase the cooling efficiency.

Now all I have to do is find someplace locally that has "high performance" thermostats. Auto Zone and Pep Boys don't even know what they are. Then again it was fun watching the look on their face when they asked what year car it was for and I told them a 1954 Chrysler. They just stood there with dumb looks on their face (since their computer system doesn't go back that far) till I said, how about a 1970 Dodge 340 small block. It's the same size as the early hemi but still no luck. Nothing but stock replacement small diaphragm units. Guess I'll have to order one from Summit.

Centerline

 

[[email protected]]

You need to find a GOOD parts guy (gal) like my Southern Auto Debbie. Sounds like you are stuck with the usual slack-jawed mouth-breather that can barely read an application chart.

Are you sure the hi-po ones aren't hanging on the rack @ Pep Boys? I have a mind's eye view of them there. Don't ask the counter clerk. They know less than nothing.

 

[Triaged]

Let it sit and idle for 25 minutes (no thermostat) and the temp finally reached about 185-190 but wouldn't go any higher. With a functioning thermostat it should run 10 or 15 degrees cooler since the thermostat will allow the coolant to stay in the radiator a little longer which will increase the cooling efficiency.

Now all I have to do is find someplace locally that has "high performance" thermostats.

Centerline

I have never believed the "theory" that a restriction in your cooling system causing the flow to go down will help it keep cool. T-stat's are put in to keep motors hotter...without a t-stat they run way too cold.

185-190 is very hot for a motor with no t-stat in it. Putting in any t-stat will just make it run hotter (because of less coolant flow even when all the way open). This is why you are going to try and find a "performance" t-stat...they flow more. If those temps are accurate you might have other cooling problems.

Does your motor have any way to circulate the water while the t-stat is closed? This is done from the factory by a small bypass hole in the pump or coolant going thru the heater core. If water dosen't circulate during warm up you need to drill a small hole in the t-stat (1/8" should do the trick)

 

[TurboS10]

I have never believed the "theory" that a restriction in your cooling system causing the flow to go down will help it keep cool. T-stat's are put in to keep motors hotter...without a t-stat they run way too cold.

Ditto, but I dont try and argue. The radiator is designed to reject so much heat.....period. This is based on air flow and heat differential from the water to the air. The flow rate of the water has nothing to do with this. With no thermostat or a failed open theremostat(if that ever happened) will cause the engine to run cold, not hot.

Chris