Overheating

[Anonymous]

Hi all,

I'm still having a problem overheating. I started having this problem after replacing the head on my car. I thought I had the thermostat in backwards so I turned it around, Wrong. It was in right to begin with but I convinced myself that I had it in backward. It ran fine for a few days and then started overheating again. I took it in and had it flushed and refilled, that's when they told me the thermostat was backwards. They put in a new thermostat and a new radiator cap. It ran good for a couple days and then today hot again. The upper radiator hose is hot and the bottom is cool so that leads me to think thermostat but it's the second new one in a couple leaks.

How about an air bubble? I've read that our cars don't suffer this problem much but it seems to have the right symptoms. I'm going to take the thermostat out to drive home tonight to see if it will stay cool. I've heard you can drill a .125" hole in the thermostat to prevent the air bubble problem but I have no idea where to drill it. The bottom hose is spring reinforced and is still quite stiff so I don't think it's sucking shut. I can't drive without a thermostat because I have a water heated choke. Kind of need the hot water to open it.

Any ideas, suggestions,

Thanks Bob

 

[69.5Mav]

+68coupe+
Most thermostats have a hole already in them. Look for the hole in the flat mounting surface about 1/4 in from the outside edge. the use of a lite on the other side of the thermostat can greatly aid in finding the hole or port. The port should be mounted up toward the top of the engine.

I would recomend getting a cheap dial type kitchen thermometer (around $5.00) from youre local food store. put the thermometer in the open radiator, run the engine and note what the reading opn the thermometer and the temp gage in youre car is. You can check the accuracy of the thermonmeter in boiling water lon youre stove. Water boils at 212 degrees fairinhiet at sea level.

Also you can get one of those clear plastic inline colant filters and install it in youre upper radiator hose. This will not only filter debree from youre colant but also allow you to see how much colant is in the system and how much is flowing.

69.5mav

 

[PLP6400]

Your upper hose should be warmer than the bottom one. The top hose is coolant leaving the engine and the bottom is coolant that has been cooled by the radiator going into the engine. Did you have the radiator flushed while it was in the car? If not, it could have plugged up again.

 

[Anonymous]

Ah Shoot! I pulled out the thermostat and was refilling the radiator with water. I had the engine running while filling with water when I saw water running out of the engine behind the exhaust manifold. I hope this is only a head gasket. Well I guess I get to pull the head again. Wonder what I did wrong. I used #8 washers under the head bolts, torqued in three stages with a wait between each stage.

What are the causes of a blown head gasket? I was getting on it a little earlier in the day not real hard but I was into it a little pulling into traffic. I heard a popping noise, smelled antifreeze and that's when it started getting hot again. Should've known that was the head gasket going.

Any advice to try and prevent future occurances of this would sure be appreciated. I'm not as good as Does10s it took me all weekend to change the head the last time.

And I just did the oil change with Mobile One. Anyone want to buy a nice 68 coupe?

Bob

 

[Anonymous]

Did you have the head checked for straightness last time or did you just change the gasket?

Take the head to a machine shop and have them true the head up...my machinist will do it for $25.00

Make sure the gasket surface is clean, clean, clean!!! I have a 3M rubber rotary disc thingy that goes on my die grinder to clean the block & head.

I like using Fel Pro head gaskets because they have a extra sealing surface on them....cortico might have the same thing...I dont remember

Make sure all the bolt holes in the block are clean so you are getting a good torque reading.

I drill a 1/8" hole in the top of every thermostat I install. Just make sure you dont hit the valve itself And place the hole at the top of the thermastat.

Later,

Doug

 

[wsa111]

I agree when you put a thermostat in it is wise to drill a .062 hole at the top or the thermostat to allow air to escape to eliminate the violent burping of coolant you get with no bleed.

On the 3.8 chevy or buick engine they have a nice one way check valve built into the thermostat, unfortuneley this thermostat is to small in diameter for our engines.

Does anyone know of an OEM thermostat the correct diameter with this one way check valve for our application??

I'l do some checking. William

 

[69.5Mav]

+68coupe+
It is important to make sure that the thermostat does not already have a hole in it. With two holes you could have one of them lower than the other which could give you problems bleading all the air out of the system. In thirty years of changing thermostats I have never seen one without a blead hole, that not to say that they don't exsist just be sure what you've got before you start drilling.
Nissan has a one way valve in their thermostats called a jiggle valve. I found this on my 82 sentra. It's to small for ford sixs but they might have a bigger one.
You should check youre block for flatness while you've got the head off a set of feller gages and a flat straigh edge will do the job well enough to determin if you need to involve youre machinist.

Good luck
69.5mav

 

[Anonymous]

Thanks for all the replies. I'll pull the head off tonight and check the block and the head. To deck the block will I need to pull it apart? Didn't really want to get into a rebuild just yet.

I'm hoping it's just my workmanship. I may not have gotten things clean enough. My washers may not have been thick enough. It's a 77 250 head that's been milled .060", wouldn't that be almost the same has the original 68 head. My chambers are now 51cc and the original is 53cc.

Bob

 

[Anonymous]

Hi guys,

Pulled the head and everything looks good. ??? The water was coming out on the exhaust side of the motor underneath the manifold between 3 and 4. Since there are no water jackets in the head there it now doesn't seem possible for it to have been the head. The water was also coming out very fast. Freeze plug?

New plan. Put the head back on with new head gasket and start it up with the exhasut manifold off to see where the water is coming from. There is no water in the oil. What would cause a freeze plug to blow out like that. It seems that the water system is under higher pressure than it should be. The shop put on a new radiator cap when they flushed and filled the system. I heard an audible pop when whatever blew.

Bob

 

[MustangSix]

There are 1" core plugs in the head under the exhaust manifold.

 

[JackFish]

I'm hoping it's just my workmanship. I may not have gotten things clean enough. My washers may not have been thick enough.
Bob

Maybe some dirt in the boltholes?

 

[Anonymous]

Jackfish,

I did chase the bolt hole with a bottom tap prior to putting it together.

Jack,
You hit the nail on the head. I had a big one inch hole in the side of the head pumping all the water out. Didn't have to put it together to figure that one out. Thanks. New freeze plug 89 cents and put it back together. Got the freeze plug part done. But I almost gave myself a heat stroke putting it back together. All I have left is final torque and the carb and plug wires.

Now, I wonder why a plug blew out? Is this common? All the other plugs are in good shape no rust or anything. The new plug went in nice and tight. Could it have been the air bubble heating up in the head until it blew out?

Thanks again to everyone helping me figure out my problem yet again. I hope I can correct the cause by drilling the hole in the thermostat. Thanks for that tip Doug, I stole it of your web site. Is there anything else I need to know about filling the coolant system back up to prevent an air bubble besides drilling the hole.

Bob

 

[Anonymous]

Maybe the freeze plug was corroded or wasnt put in correctly at some time in the past??
I could be wrong but it shouldnt be pressure or anything like that because your radiator cap should release the pressure 1st or if it didnt you should blow a hose or the radiator before you would blow a plug out.

Thanks for that tip Doug, I stole it of your web site. Is there anything else I need to know about filling the coolant system back up to prevent an air bubble besides drilling the hole.

No problem!

Just use a 50/50 mix of antifreeze and water. I also recently started using that redline "water wetter' and it seems to work pretty well for me!

Just curious, but what is the pressure rating on the raditor cap? It should be stamped in the top.

Later,

Doug

 

[Anonymous]

All,

Well I think it's fixed. I put the head back on without the thermostat and ran it really hard on a hot day and I never even got half way on the gauge. Most of the time it was only about a quarter of the way. I was running about 80 miles an hour for awhile and then idling in traffic when it got to almost half. After I got out of traffic and cruised at 60 for awhile it had dropped back down to a quarter of the way.

I'll drill the hole in the thermostat and replace it. My theory on what happened is that I had an air bubble behind the thermostat not allowing it to open properly and the steam built up until it blew the plug out. All the plugs that are in there look like they are relatively new and are in good shape.

Doug the cap is a new 13 pound cap. The shop that did my flush n fill replace my pretty chrome one with it because they said mine wasn't holding pressure. I put a pressure guage on the radiator with the car running and I don't have an overpressure situation which is good.

Thanks again for all the help everyone.

P.S. I'm getting better pulling and replacing the head. 4 hours start to finish. I'm closing in on you Does10s. LOL

Bob