Overheating

[zzrodder]

Sounds like you've been doing the right things but it still shouldn't be getting that high while driving. From your description of the rad's location, it sounds like the crossmember is partially obstructing the airflow? If it cools down when the engine is going slower it sounds like an airflow problem --- how is the air ducted thru the grille to the rad? Is there a way for the air to go over or around the rad instead of thru it? Some shrouding in front of the rad to the grille opening may be in order...
Another possibility is that the lower rad hose (intake) may be collapsing as the engine revs up, especially if it is a soft hose or has somewhat kinked bends. You can get hoses that have a spiral wire like a spring inside to prevent that happening.

 

[CR55]

If it gets hot while driving at highway speed but cools down at an idle, its an airflow problem...had the same thing on a vette once..

 

[NitroJohnny]

I considered the airflow being an issue. The radiator is in front of the cross member so it isnt being blocked. You can see the picture of the front of the truck. All there is is a bent up original grill. I thought about ducting the front to force air through the Rad but that would be tough on this truck and I really dont want to do that if theres another issue that could cause it.

 

[RPM]

What thermostat have you got in it? 200 degrees is not hot and nothing at all to worry about.

 

[NitroJohnny]

Its a 180. Newer engines are designed to work at higher temps. Even up to about 230. But these old engines work best at 180 or close. I know 200 isnt horrible, but there is a limit to most engines that once it gets to a certain temp, it just shoots up quick and you cant get it back down. Temps here are currently about 73 degrees during the day. If it gets to 190 now, what do you think is going to happen in July when the ambent temps are 100+ ?? I wont be able to drive it down the street. So I need to get it right now and be ready for the heat.

 

[zzrodder]

I considered the airflow being an issue. The radiator is in front of the cross member so it isnt being blocked. You can see the picture of the front of the truck. All there is is a bent up original grill. I thought about ducting the front to force air through the Rad but that would be tough on this truck and I really dont want to do that if theres another issue that could cause it.

For an easy way to see if airflow is passing around or over the rad and causing it to heat up, break out the good ol' duct tape, hay wire and cardboard. Create panels bridging the gap between the rad and the grille so all air coming thru the grille is ducted to the rad.
Do a test drive, hey, the worst that can happen is some cardboard flies off --- but it should hang in there long enough to tell you if it works. Gotta be easier than the engine work you've already done.

 

[NitroJohnny]

Made a shroud out of aluminum for the front, race car style. Not totally sealed but should work. Thats when I drove it about 10 miles and got to 190. I think it would have ent higher, but I slowed down. Outside temp was about 75 maybe. I was asked on another forum to look at the exhaust flap to make sure it wasnt closed some. I'll be checking that as soon as I get the time.

 

[LOWANDRATY]

overheating

The cooling fan in front of the radiator may be the problem, a fan in front of the rad. cools about 1/4 less than a fan behind the radiator, do you have enough room to move the fan, and get a good cap on it. if it will run at 190 to 200 all the time that is ok. If the system stays under 180 the thermostat will not open and thats not a good thing, once it is open you want it to stay open, and not cycle open / shut.

 

[NitroJohnny]

I guess you missed that part. LOL The fan is behind the radiator. Its a puller system now. I'm just trying to find the reason for it running hotter only when driving at 50mph or over. ( Estimated speed due to no speedo )

 

[sgtpontiac]

I would think it's a flow issue....

either the pump isn't moving it fast enough or it's moving it too fast....I didn't go back and check the motor type......if there is a diverter plate behind the pump, needs to be there..can't take it out....

If not it, Then I have seen pumps that appear good and move water when idling...but...I have seen impellers that slip at higher under higher flow conditions...the pump is turning like heck and the impeller is not...would cause the issues / symptoms you are encountering..... no way to tell if that is happening other than to replace the pump....chrysler used to have a lot of problems like that especially with rebuilt pumps...just a thought....

 

[NitroJohnny]

It has a new pump. And the old pump wasnt that old at all and seemed to work just the same. I dont remember seeing any diverter plate. That may be my issue. Its a 69 250. If I can remember this, I think with the pump off, I could see the #1 cylinder. Basically just a big hole.

 

[hotrod preacher]

is it possible that there is a collapsing hose? as we all know those springs in lower radiator hoses help keep them from sucking together... just a "grasping at straws" thought

i also know that not every hose has a spring in it but a collapsing hose might be worth looking into

 

[NitroJohnny]

Theres no spring in this one because I had to make it from tow different hoses. But its all new and really stiff. I dont think it can collapse especially with this water pump. They dont seem to move too much water too fast.

 

[hotrod preacher]

timing issues might do the same thing... im not sure [S

 

[NitroJohnny]

I checked TDC while the head was off and it's dead on. I did set it to 12. I could bring it back down a little to see if that helps. I used to run my stock car engines at 32-36 degrees advanced with a locked dizzy and didnt have this hard a time keeping it cool.

The one thing I dont know about is the dizzy itself. When vacume is hooked up at idle, it goes to full advance. Maybe weak springs? I dont remember what it went to in degrees, but I think it was about 27. That number sticks in my brain for some reason but its been a while.

 

[PA41]

I checked TDC while the head was off and it's dead on. I did set it to 12. I could bring it back down a little to see if that helps. I used to run my stock car engines at 32-36 degrees advanced with a locked dizzy and didnt have this hard a time keeping it cool.

The one thing I dont know about is the dizzy itself. When vacume is hooked up at idle, it goes to full advance. Maybe weak springs? I dont remember what it went to in degrees, but I think it was about 27. That number sticks in my brain for some reason but its been a while.

That part of the situation sounds like you have the dizzy vac line hooked to the wrong port in the carb/intake. I realize you have checked that, but you might revisit the vacume layout. It needs to be hooked to a port where the vac increases as the throttle is opened. If the vac port really increases with the throttle, then it would be the dizzy.

PA41

 

[NitroJohnny]

Its hooked to the only open port on the carb which is on the base plate. But I dont know if this is ported above or below the throttle plate. Should be in the correct location since its the only port available. I'll have to check it with my vacume guage.

 

[sgtpontiac]

You would need a crap ton of timing..

to cause it to overheat on the road...I still think it's a flow issue....for some reason.....get back to the basic's....like a flow chart....sometimes you miss the easiest things looking for the difficult ones...
Start with the engine....it's either a head gasket, cracked head...if neither exsists its in the cooling system...Radiator, water pump, hoses, cooling fan or air flow or circulation of the coolant...I'm leaving out the thermostat as you've said you replaced it....
If a head gasket were gone or the head cracked I'd think you would see some coolant loss or the radiator would pressurized very quickly....if the radiator was bad (clogged) you would see reduced flow and possibly cool spots ahead of the clog on the finned area of the radiator.... if a hose is collapsing you might be able to duplicate the driving down the road by simply bringing the engine speed up to highway speed and watching the hoses.....I guess what i'm saying is go back and start at the beginning and forget what you've already checked and start over....for the timing to effect the cooling issue would result in a lot of spark knocking and such... some engines run vac advance at idle for emissions reason.....can be changed to ported vacuum without a problem....JMHO...start back at the beginning and go back thru it like a flow chart, eliminate the basic stuff first and move on to ultimately find the problem....JMHO

 

[sgtpontiac]

Ok..went back to the begining of your post...

Quick question since I am not figuring it out on my own. I have a 250 L6 Chevy. Had the radiator cleaned and repaired. Best it could be repaired. Several tubes are closed off and it does have damage. So I know its not the best Radiator but shouldnt act like it does now. New water pump and 180 thermostat. New electric fan without shroud pushing good air. 3 Core Radiator. I dont know what it is out of. Has top and bottom tank. 2 inlets on the top and one on the bottom on passenger side. Maybe someone knows what it is out of.

I can drive it about 2 blocks and it hits over 200. Tstat opens around 200-210 gets back down to 170 range and shuts. I dont like the late opening so I am going to change it. It ramps back up and drops a couple of times due to cool water getting to the engine of course. But then keeps heating up to about 220 max before I shut it off. I dont know if it will go higher since I am not going to run it and see how high it will get.

It does need a new cap. Tried 3 that I had laying around that I used on my old race cars. And none seem to hold pressure at all. Even 190 degree pressure once the engine is shut off. Running it holds. Shut it off and they release pressure and water. Caps up to 16psi.

Also I can have it idle in the driveway for quite a while and not dirve it. Seems to stay at around 180-190 for 15 minutes or so and I think all is good so I shut it down. Drive it and it heats right up.

I have reset the timing a couple of times. It was at a base timing of 12 degrees advanced. I have gone to 4 degrees to try and help it. I have found that 4 degrees is what it is supposed to be set at. But once the vacuume is hooked up the dizzy goes full advance and is idleing at around 26 degrees. I was thinking week springs but maybe they are supposed to run like this. This is my first old straight 6 engine. I always run V8 engines with HEI distributors and Mechanical advance.

So thats for the help. BTW it is about 70 degrees here outside temps now. This engine should not heat up this fast.

Not to beat a dead horse....I went back to the original post.....
A few things i've noted.....the radiator issue...do you know for sure these things are any good.....2 row 3 row means nothing if it's clogged or has areas closed off and soldered up...
Radiator Caps.....unless the water is boiling over and or the pressure is too high (possible head gasket issue), the caps should not blow off when you shut it off....if you've tried 3 caps of unknown condition buy a new one, they are cheap...
As for the timing......again JMHO..the timing sounds like you have it right so I would rule that out unless you can't really check or confirm the timing for sure......
I would encourage you to start back at the beginning....confirm that the head isn't pushing combustion back into the radiator and that the radiator is moving water and air properly....from the original post, I'd be looking for a bad head gasket and or cracked head....again JMHO...sorry I didn't check back into the post from the beginning....

 

[NitroJohnny]

Thanks for the advice, but it looks like you missed my updated post. Head is fine and been rebuilt. Gasket looked ok, but could have been the issue. So top end is complete and not the issue. Radiator is brand new, including the fan and shroud. Water pump and Tstat is also brand new. The old pump worked fine, I just replaced it because it was cheap and I didnt want future problems.

I agree that the timing shouldnt be the issue. no knocking or pinging, and it runs just fine.

I am leaning towards gunk in the block may be the issue. So that will be cleaned. I will check the lower hose to be sure it isnt collapsing.