Overheating

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.

If the system will not hold pressure, it will overheat every time.

If anyone is in doubt, drive it with no cap, or the cap loose =)

Are you sure the fan is running in the right direction?

rainman said:

Are you sure the fan is running in the right direction?

Click to expand...

That's actually a good question, I wired mine backwards the first time, felt right when I put my hand down there, till I stuck a piece of paper on the front of the rad and it blew it off instead of sucking it toward the core. It seems to cool better now.....

I have also been led to understand a puller is better than a pusher.

Cheers

Fan is correct. I always check that. I'm not knew to this at all. Owned a shop and worked as a tech for 2 dealers. But these old 6 cylinders are kind of new to me. I just wanted to see what your opinions were. Since it doesnt overheat until I drive it I thought it may be timing too advanced. Due to it heats up so fast when driving.

On the cap. you are correct. Higher pressure cap will raise the boiling point and allow for hotter water temps. But be carfefull that you dont over pressurize an old radiator and buldge the tanks. I am pretty sure mine are junk so it is getting a new one.

I went ahead and ordered a new aluminum radiator just now with shroud and fan. Also a new cap and overflow tank. This should take care of it. I will check for air pockects when I get it going again.

I just started with the cap, as its a known bad item per your description, but I agree with your plan for certain.

With the engine at idle and the cap off, radiator completely full. Do you see any air bubbles coming to the top of the coolant. Leaky head gasket or a crack if there is. What do you have for a grill in front of the radiator? Sounds like there is not enough air going across the core to take away the heat. Can you post a few pics of the front of this car?

It get a few bubbles when the Tstat opens and lets a little air out. I havent had it run long enough to really get the system burped properly. At least I dont think so. I dont have any oil in the water , and no water in the oil. I have done a compression test when I first got it home and 1 cylinder was a little lower than the others, but not that much.

Not much can be done for the front end.

Hey Nitro, are you positive that the timing marks on the harmonic balancer are in the right place? I've seen a few where the outside of the balancer will rotate a little, on the rubber, and throw the marks off. In my expierience, running retarded will make it heat up. If it's too far advanced, it'll be hard starting hot and probably ping a lot. I had an old Courier pickup that was overheating one day and when I opened the hood to check things out, the exhaust manifold was glowing a good cherry red. The distributor had loosened and retarded the timing enough to heat it up good. You could've lit a smoke off that exhaust. But, I would check the TDC mark on the balancer just for the heck of it anyway. Good luck.

Sure sounds like a head gasket leaking if you are still seeing bubbles come up after the T-stat opens, especially if you've already driven it, it should already have moved the air out of the system. You won't always get water in the oil or oil in the water if it's leaking, but it will sure heat up fast.
Of course a new rad can never hurt and may really be the problem, sure beats pulling the head..

Yea, I thought about that too. I was going to check it yesterday but couldnt find my remote start button. I have a TDC checker but need a way to bump the motor since there isnt a bolt in the balancer like the newer engines. I am going to check that as well.

When I bought this truck and checked it out, it had a base timing of about 12 degrees. I lowered that to 10 since I thought it was too high. I might bump it to 14 and see what happens. I do know at 4 degrees it sounds very retarded.

Another common prob is changing the size of the pulleys! That can speed up or slow the water flow & either one can spell trouble! Check out what size pulleys that motor is supposed to run. March & other companies sell underdrive sets that are supposed to increase HP but can cause cooling probs! Just a thought if nothing else works! Also prefer puller elec fans over pushers! I only use a pusher if i have no other choice!

BoB

Bob, I prefer pullers too. But on this truck the body is dropped 10 inches so the radiator sits well below the old radiator support and there isnt room for a big enough puller fan. The motor sits low too and the water pump pulley is too close the the member as well.

It has stock pulleys and I gave some thought to a smaller pulley to speed it up a little. I dont think thats an issue though. And yes, pulleys can cause issues. If you drive a pump too fast it can cavitate and stop flowing all together but it takes a lot of rpm do do that. I doubt this little 6 will ever see that kind of rpm so it probably wouldnt be an issue really. But I like stock stuff and will try to make this work.

I'm going to try another Tstat. Might drill a small hole in it to help get air out easier. Bump the timing to about 12 degrees. I have read different timing settings for this motor. 10 and 4. It was at 10 when I bought it. But I found the 4 somewhere and reset it. That may be part of the problem too. Plus a new cap. Maybe all of these combined will solve my problem.

Then if all that fails, I have the new radiator with shroud and fan coming. Puller setup. The radiator brackets have it laying back at the top so it pushes the bottom toward the bumper. Which gives me a little more room for the fan. And I can trim a little support if I have to.

I'm also going to do a leak down test to be sure its not a head gasket. I dont think it is, but you never know. I've had head gaskets blow on race motors but they always introduced water into the oil so you knew you had an issue. This one isnt doing that. So my fingers are crossed that its fine.

You are getting good oil circulation at all RPM? Just another thought.

If you are starting it cold, driving it 2 blocks and it is hitting 200, it has to be the engine. So did you idle it for awhile before driving? What was the initial temp when you took off?

What I'm getting at, is the radiator shouldn't even be necessary in that short amount of time. Therefore somehow you are creating tons of heat quickly.

I agree. That why I was asking more for the motor itself. I did install a new cap. 16lbs. New tstat ( again ) and reset timing to 12 degrees. Started it up and let it run. By the time it was at 150 it was already pushing water past the new cap. I think I have a bad head gasket. As was mentioned earlier. But now water and oil mixing so I was hopeing against that. I am going to borrow a leak down tester and check it.

So either its the head gasket or the head itself. OR, I go get my buddies back up 355 chevy race motor and drop it in. Either way its more work than I want to do. I'm kind of tired of working on cars and trucks. LOL

If it has sat for an extended amount of time it's possible the block could be corroded, and gunked up!! Could explain why it idles cool but rises under load!! If memory serves me right those inlines where kind of prone to
partially blocking themselves!!
Once you've tried a few of these other ideas, you might want to try and flush it!! Just a thought!!

Never mind just saw your last post!!

Yea I saw the inside of the block when I had the pump off. Looked really clean. I think its the head or gasket. Unfortunatly.

"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."
When you get the compression leak fixed, the vacuum advance line goes on the venturi port and not the manifold vacuum port. Both of these ports are on the carb, manifold will pull vacuum all the time and the venturi will only pull vacuum when the throttle is opened.

Its hooked up at the correct carb location. I have the manifold vacuum going to the vacuum modulator on the trany.

Ok, time for an update.

I installed a new Champion 2 core aluminum radiater with shroud and electric fan. Pull not pushing air. Had the head cleaned up and it had to be cut 14 thousanths. I never really saw a bad spot on the head gasket, but I think it was leaking a little.

Drove it today. Ran up to 190 for most of the drive, then on the way home climbed to over 200. Went about 15 miles each way. I had the exhaust pipe installed. I dont have a speedo so I guess I was going about 55mph. Not turning high rpm. No tach either yet. If you slow down or stop and let it idle, it would cool back down to about 185 or so. Timing was the same as I last set it. I think I bumped to 12 degrees to try and cool it down.

Any ideas?