Overheating and high pressure on my 73 400

[WH23G3G]

Also when I drove it to the shop today to get the alignment checked the coolant gauge needle pegged out at H. It was only about 5 miles and we weren't going over 45MPH. We stopped for 20 minutes and checked under the hood. You could hear the coolant boiling in the overflow jar. I have a pressure release cap on it and when I lifted the valve you could hear the high pressure flowing back into the resevoir. It seemed like there was too much pressure. The upper hose was so hard with pressure you couldn't even flex it. So we turned on the heat which was super hot and just took it home. Once we got going and the heat was on it went back to the middle. Now I know the carburetor I've been told is junk, it wants to die if you stop. I've got an original one being built now. I know theres a lot more friction since all the internals are new but I don't think it should be getting this hot. It's got a new water pump, 180 thermostat, and new oversized radiator, and 7 blade A/C fan, plus new HD fan clutch I didn't even hear come on. Is there something I need to check?

[elacruze]

There's a lot to think about here.

Is the thermostat in upside-down? Is the radiator temperature lower than the engine temperature?
If your fan clutch didn't come on you could simply have no water exchange with the radiator, keeping rad temp low but engine temp high. The pressure will remain constant throughout the system, however.

Do you have a 440 source water pump housing? They are a known cooling issue.

[WH23G3G]

No I have a new store bought water pump, not a remanufactured one. No leaks anywhere. Heater operation is good. I assume the thermostat is working since the upper hose was pressurized. I remember when we first got the engine in and on initial startup we had a 180 Failsafe thermostat in and it got stuck open right away. So I put in a Mopar Performance 180 thermostat now. I have a 160 on the shelf but didn't want to put it in yet or maybe at all. I couldn't verify if the radiator was hotter than the engine, I'm sure the engine was hotter just by feel but I didn't have a thermometer with me. I have a 16PSI radiator cap on with the release lever and I know when I flipped up the lever you could feel the coolant gushing back into the overflow resevoir. I've only heard the fan clutch kick on one time when it was idling in my garage and the temp got up to H but it was after it was already at H. I have a brand new bypass valve hooked up too. I followed the checklist through the 73 Chrysler dealer service manual and it pointed to a thermostat, but why? I'm almost thinking that maybe the carburetor problem is causing this issue too since it idles so low when you come to a stop it wants to shut off. Maybe the fan isn't spinning fast enough. My original Thermoquad should be redone this week. I took it to be rebuilt by the Demon Sizzler since he's only 15 minutes away. 

[elacruze]

You can't do much without a thermometer, preferably an infrared unit so you can test various points under the hood.

Thermostats control water flow, but they do not affect system pressure since the lower hose has a direct path to the engine. In a fluid system, if any point is pressurized by heat, the pressure will equalize throughout the system. I've seen a lot of cars up north overheat and die because the radiator froze solid once the car was moving (due to poor antifreeze) The water can't circulate, the engine coolant boils and pushes out the radiator cap (since the upper hose and rad top are rarely void of air)

It's possible to install a thermostat upside down, and since then the temperature sensing spring is on the cold side it may not open. Flow is restricted to the radiator and the system can't cool. It's important to know that the vehicle's heater is a separate system from the radiator, and can be very hot even while the radiator is cold (designed so that you get interior heat as quickly as possible)

Fan clutches do not engage until the air flowing across them reaches something like 220* F. Again, the lack of clutch activation points towards a low radiator temperature.

With the car cold or cool enough to remove the radiator cap, use a turkey thermometer to test the coolant temperature directly. With the cap off you can verify flow into the radiator and the coolant level as well.

Also, since you've had the coolant out, you probably have some air pockets in the engine block that need to be purged. Air will show a much higher temperature to the gauge sensor than water will. To purge air pockets you may have to rev the engine up high a few times with the cap off to get enough water flowing to flush it out.

Your water pump is not in question, rather the housing that the pump installs to. If it's a factory iron unit, you're good. If it's aluminum, it's suspect for flow, although at low speeds shouldn't be an issue. Another problem with overheating is retarded ignition timing-you should have somewhere around 30* total at idle.

[WH23G3G]

I do have a digital thermometer just didn't have it with me when I was driving it. I can tell that the engine was much hotter than the radiator. After we got it home and it cooled for about 2 hours you could tell the radiator was cool to the touch but the engine was still much warmer. I don't know what the timing is suppose to be total degrees but I've got it on 10 degrees BTC where it should be. That's the factory setting and it doesn't ping but you can't tell about power because the carburetor is garbage. I'm suppose to pick up my 6321S Thermoquad rebuilt tomorrow from Demon Sizzler and hopefully it will make some difference in the way this motor idles and runs. I know when we were driving around the engine probably wasn't running maybe 700 RPM at idle because if we let off the gas it would shut off.

[WH23G3G]

I took off the water outlet and upper hose and sure enough the thermostat was stuck. I don't know if it's stuck open or closed I can't tell. The little pellet in the center on the bottom is stuck out. I don't think that's right because it was flat when I got it. So I think there is something wrong with it. This a Mopar Performance 180 thermostat or Mr. Gasket I can't remember. When we initially started up the engine we had a 180 Failsafe thermostat and it got stuck on the first startup and still ran hot. So that's two in a row. Why would that happen? I just put a 160 degree that I had sitting around new, but also a Failsafe. Any recommendations?

[elacruze]

Most common service items are junk, made in China and China has no quality control to speak of. I had a very long partially heated discussion once at NAPA over radiator caps; I bought one which had no spring on the vacuum plate. It just dangled. I explained that with no spring, the valve couldn't close, and it couldn't pressurize. They assured me that the pressure would close the plate...um...not. So we eventually went through all their radiator caps, and found one or two out of a dozen that had springs as they should...point proven and point taken. New doesn't mean good.

[71bee]

Most common service items are junk, made in China and China has no quality control to speak of. I had a very long partially heated discussion once at NAPA over radiator caps; I bought one which had no spring on the vacuum plate. It just dangled. I explained that with no spring, the valve couldn't close, and it couldn't pressurize. They assured me that the pressure would close the plate...um...not. So we eventually went through all their radiator caps, and found one or two out of a dozen that had springs as they should...point proven and point taken. New doesn't mean good.

Agreed! most of the new parts you find @ A.Z., O'reilly's & even NAPA these days are made in China: crapola. be extremely careful what you purchase for your classic cruiser. to think that a poorly made $10 part could destroy your classic big block just boils me.

[WH23G3G]

I believe the thermostat I just took out that was stuck was a Mopar Performance high flow. I wanted to get an NOS coolant reserve type radiator cap but they don't exsist anymore. I saw an NOS one on EBAY last week and I'm not sure how high it went to. Is anyone redoing the special coolant reserve caps for 73 B and E bodies?

[71bee]

I believe the thermostat I just took out that was stuck was a Mopar Performance high flow. I wanted to get an NOS coolant reserve type radiator cap but they don't exsist anymore. I saw an NOS one on EBAY last week and I'm not sure how high it went to. Is anyone redoing the special coolant reserve caps for 73 B and E bodies?

Ready for a shocker? some of the MOPAR PERFORMANCE products are also out-sourced to China & other parts of the world. good ol' "American made" is a thing of the past. we better get our shit together before we're done for. 

[WH23G3G]

What do I do then? Do I keep trying the aftermarket thermostats until I get a good one or do I try and find an NOS one? I had yet another Failsafe thermostat new in the box in my garage it's a 160 though, but I went ahead and put it in. I idled with the new carb, idles much better with the rebuilt carb and it didn't overheat. Had it running for about 15-20 minutes of course it was about 50 degrees outside too so I won't know until I drive it again, hopefully this weekend. One mechanic told me I could run it without a thermostat and see if it still overheats. Is that a good thing to try?

[Cooter]

Without a thermostat will definately cause it to overheat due to moving the coolant too fast through the system. Has to have time to stop and cool in the radiator before being pumped back to the hot engine. Will take a long time to get hot, but once there, it will take forever to cool off.


Your assuming it's the Thermostat. Have you actually done what Elacruze said, and checked the coolant with a thermometer? Is it actually overheating, or are you over-reacting?

[Mopar2u]

I always tested the old/suspect thermostats in a pan of boiling water (212 deg). Boil some water, hang the stat with wire, and lower it in and watch it open (or not.) Now I even test the new ones before install...  If you have a thermometer, you can heat the water to test the stat opens at a given temp.

I guess we have to be our own quality inspectors these days.

[elacruze]

I always tested the old/suspect thermostats in a pan of boiling water (212 deg). Boil some water, hang the stat with wire, and lower it in and watch it open (or not.) Now I even test the new ones before install...  If you have a thermometer, you can heat the water to test the stat opens at a given temp.

I guess we have to be our own quality inspectors these days.

If you don't have one already you can get a little thermometer at the auto parts for less than $10. An easy way to tell approximate temperature is with your hands; 150*F is about the upper level of being able to hold on to something very long. If your hands are calloused and hardened, you can just about hold on to your upper radiator hose if it's not overheating. If it actually goes above 200*, you won't hold it long.

[71bee]

I always drill a couple of small holes in mine. some may think it's a little crazy, but I'm not having any over-heating issues. just takes a little longer to warm up in the winter. 

[WH23G3G]

So maybe the first time this happened it wasn't thermostat either. I checked this high flow Mopar one in a pan of boiling water tonight, although I just placed it in there I didn't hold it by a string. I've got a digital laser thermometer and it opened at 180 just like it should. But I thought the little pellet on the bottom side of the thermostat should be flush level when the thermostat is room temp but maybe not. It still isn't but it opened at 180. Now how to I check to see if the water pump is bad? I tested it the other night after I got my rebuilt carb on had it idling for about 15-20 minutes but didn't see the water in the radiator moving at all but the new 160 thermostat hadn't opened up yet either so that didn't help. The water pump is pretty basic what usually keeps it from pumping? I put a new one on when I rebuilt the engine.

[71bee]

you could have a bad pump. have you noticed water leaking out of the weep hole? any noise?  maybe you need your radiator flushed or re-cored. sounds like you got blockage of some sort.

[WH23G3G]

There is no leakage at all or even a smell of antifreeze. When I had the engine out for rebuilding I thouroughly cleaned it and all the passages before I took it to the machine shop. They hot tanked and washed it. Then when I got it back I cleaned out everything again all passages and oil holes. There is no noise. I don't know if it's possible. But the carb was running so bad it nearly would die if you took your foot off the gas. I believe it had some vacuum leaks so the engine was never spinning very fast and maybe that caused some overheating issues. After it overheated and we pulled over for 15-20 minutes then we hurried back home going a little faster to get air in the radiator, the gauge went back to normal all the way home. The heater has got good heat so doesn't that mean water is being pumped into the heater control valve. I've got the new 160 thermostat in and my rebuilt carb on and if it's nice the next time I'm off I'm going to run it around the neighborhood enough until it gets hot. I also put on a new radiator cap without the release lever on it.

[elacruze]

Nobody's asked about your timing yet, did we? Retarded timing will make a lot of heat at low speeds.

[71bee]

Nobody's asked about your timing yet, did we? Retarded timing will make a lot of heat at low speeds.

 true! I had a slight issue with this exact problem a few years back. always check the simplest things first....I didn't, & it cost me a few hairs!  

[WH23G3G]

All I know about the timing is to mark it and set it with a timing light. I've got it at 10, which is the recommended timing in the specs I have for 1973. I have a stock cam and ignition system. It doesn't ping or backfire. I don't understand all the technical aspects of ignition timing I just know how to set it to a spec but other than the overheating it shows no signs of the timing being out. I think the carb has made so much difference. I just have to get a good day to  get out and drive until it's warmed up completely and see if it overheats. It's looking like maybe the start of the week now before I'll have it out. There's no play on the water pump shaft and there's no noise coming from it. I checked to see what fan I had. It's the big 7 blade A/C fan and the new clutch seems to be ok nothing noticeably wrong. I'm running a very nice original 28" shroud and new radiator. I even have the new air baffles installed ontop of the front air dam. I'll get it out and run it around again. Maybe that old crappy carb was keeping the RPM too low and tended to overheat? Well I'll see.

[elacruze]

With stock cam and compression, stock may be ok-but I think it would probably like 2-4* more.
Take the cap off, and verify that your mechanical advance isn't frozen. Suck on your vacuum advance pot and be sure it rotates under vacuum, too.