OK long story short. My slant 6 engine is overheating and I don't know why. I'm not a mechanic but I like old cars so I really don't want to get rid of this car but i'm pulling my hair trying to figure this one out before throw more money at it.

What we've tried.
-New 3 row Copper Core radiator
-New waterpump
-Fan shroud (Later removed it cause it made no difference, plus it's easier to work on the car without it.)
-Engine rebuild (A 3rd party shop did this)
-Checked the timing (Explanation later on)
-New muffler, (the old one blew up, don't ask)


Modifications it has and does not have.
-390 cfm Holley Carb
-4 barrel Offenhouser manifold
-Stock Exhaust Manifold
-Stock 3 speed transmission. (~3,000 RPM on 3rd gear to stay at 65MPH highway speeds)

When I first bought the car I drove it over 100 miles from Los gatos to Sac and have take it to San Fran and even Sonoma Raceway twice. it felt slow and sluggish but it worked so it was alright and we thought it was normal. We've always had a small problem with overheating on it but we kept it under control with light driving. However once we got it rebuilt the problem got worse! Ten minutes of highway driving and the engine gets into the red zone and I have to stop to let it cool off, the water gets boiling hot and if I let it drive longer I know it will spew water out through the safety release valve on the RAD.

The engine has been over-bored by the previous owner, I don't remember to what extent but the mechanic told me this when he rebuilt the engine and assumed it was used for racing purposes. I'll be getting more information later on on this when I revisit the mechanic again.

We kept thinking it was the timing but the timing on this engine was always impossible to get right. It's supposed to be set to "0" but it we can never get it spot on and it's either too high or too low. So it's set as close as it can. Two different mechanics have tried to as well and they've told us that it's because the engine has been modified so they can't set it exactly on the dial, is this possible?

One more thing I kept thinking was the it still has the stock manifold and that the little 1 1/4 inch exhaust is causing too much back pressure. The reason for this is that if the engine has been upgraded for better performance, but will leaving the restrictive slant 6 exhaust manifold cause overheating to this extent? especially at highway speeds?

Either that or the shop rebuilt it wrong somehow and made the problem worse, but the engine idles well and definitely feels more powerful than when I took it in.

I hope I'm not running you guys in circles but any suggestions would be nice. I've been tempted to sell the car but I don't think I can get even $1000 at this point since they wouldn't even be able to drive the thing home.

No, this is BS. Your "mechanic" is either too lazy to do it right or doesn't know how to do it.
Have you replaced the thermostat or at least checked that it is opening at the correct temperature? Did the engine rebuild include cleaning the water jacket in the cylinder head and block? I would start by checking these things.

Too restrictive of an exhaust will rob you of potential fuel economy and power, but won't make the engine overheat. The stock manifold is not too small for your build. A larger exhaust system (2 1/4 inches to the muffler, 2 inches after) will help with power and economy, but won't reduce overheating.

Improper timing can cause overheating. However, the timing should easily be able to be set, but the stock setting might no longer work best for the engine combination.

Do you know the profile of the camshaft that was installed in the engine? Do you know if the cylinder head was milled or the block decked or the piston bores bored oversize? These variables will all affect the timing for the engine. Further, do you know if the stock distributor is being used or if a "high performance" disributor was installed?

You do definitely need to get the timing sorted out. I would start by using a piston stop tool to verify that the timing mark on the vibration dampener has not slipped. If it has, use paint or white-out to make a new temporary timing mark on the damper.

Next I would disassemble, clean and lubricate the distributor. Make sure the mechanical advance weights are free to move and that the springs return the weights to their resting position. While you are in there, verify that the vacuum advance pod still holds a vacuum and check the advance springs. If you have two light springs then you probably need to fine tune the timing curve. When you reinstall the distributor, be sure to hook the vacuum advance line to the carburetor, NOT the manifold.

If the camhaft has been replaced with a "high performance" cam, then you will likely need to run a different base timing than the stock "0" setting. Without knowing your cam profile and compression ratio, it is impossible for us to tell you exactly what is your 'ideal" base timing setting. It sounds like this is a street/strip car, so you will likely want to start with a base timing setting in the 8-12 BTDC range. While you have the distributor apart, look for the number stamped on the governor. Tells us what it says and we can give you a better idea of where to "ballpark" the base timing setting.

It is also possible that the shop that rebuilt the motor did not time the cam correctly, but I would verify that all external causes have been dealt with before pulling the timing chain cover off to verify the cam timing.

The more information you can tell us about the specifics of your build, the better we can help you solve your problem.

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Casually looking for a Clifford hyperpak intake for cheap.

I forgot to mention that thermostat was the first thing we replaced and when we checked it, it did open in boiling water. Heck we ran the car without it for a while, same problem and it just took longer to idle properly in the mornings.
No, that's something I will have to check. (under investigation.)

If i recall correctly I remember him complaining the piston bores bored oversized because he needed to reorder new piston rings due to size issues. (under investigation.)
I do know that the stock distributor is being used and it's a points not electrical. (I'll be taking it apart today and checking that, maybe I'll be trying different timings then.)

Thanks for all the info, I will speak with the guy and see what camshaft it has and compression ratio the engine has. In the meantime I will be playing the the distributor and see what number it has on it.

Also this was supposed to be a daily driver cruising car but for some reason the engine has been rebuilt in the past according to the last owner and for all I know it could have been poorly modified for performance.

Does it overheat at idle, no load?

0. First....Did you replace the temperature sender?

They can go bad on the first overheat cycle.
Maybe the lower radiator hose is loose letting air into the system which will cause steam and overheating issues.......or a leak in the small bypass hose between the water pump and block.

1. Do you have an overflow coolant tank so when the engine cools off it will draw water back into the radiator thus keeping it full?

2. Is the radiator cap new 16 lb version with double seals for coolant recovery?

3. Is the radiator cap surface smooth and free of defects creating a good seal at 16 lbs.

4. Have you taken a hand held laser temp gauge to verify temps?

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

This sounds like an older car if it has points. But just to be sure, it does not have a catalytic convertor on it does it?

Can you see water circulating into the radiator once the thermostat opens?

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

Yes. I am wondering if the water pump impeller is loose on the shaft.

Sam

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--Ted
Hmm I haven't replaced the temperature sender. It still seems to work but might as well.

The rad cap has seals for ~15Lb and it does have a resovior tank, i added those myself, the coolant is flowing when the engine's warm as I can see it rush through as I rev the engine. but I don't think i'll need a temperature gauge to tell me that the water is literally boiling hot as it bubbles out of the resoivor tank.

heck, just for fun on Sunday I topped off the water, warmed up the engine, checked water again and took it for a drive, and what do you know? the engine got hot, worst of all it started to rain a bit and I sure knew it wasn't the weather causing the overheating!

I've replaced the top and bottom hoses with new rubber ones and they are as stock as can be, no funny bends and a very clean direct flow. I kind of ruled out that when I tried "burping" the system to check for air gaps. I feel it's going to end up being the timing as I never paid much attention to it as I should have.

--Sean,
Yeah it starts to get hot just warming up the car, if I don't keep an eye on it, it will overheat just sitting there, even at stop lights the temperature rises a bit, the only time it doesn't get bad is at around 40MPH feathering the throttle. I assume cause the water's moving and cool air plus the light load.

--Sam
I don't know what a loose impeller on the shaft is, but the water pump should be new, and the water circulates fine, again I just think it might be ignition or engine related.

--Rick
Yeah it's a 1970, i should have mentioned that but no CAT thank goodness.


Thanks all for your suggestions, I'm making a list of what to double check[/url]

Just so you guys know what i'm dealing with here, he's a vid of the engine just warming up. I know it won't help but at least you can see what I have.

http://vid1009.photobucket.com/albums/a ... EO0012.mp4

Where is your PCV valve?

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Casually looking for a Clifford hyperpak intake for cheap.

I have had one and my brother-in-law had one also (impeller loose on the shaft higher motor speed makes them slip on the shaft).

Richard

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Part of Tyrde-Browne Racing

Bingo!

This is classic symptom of internal water pump failure. At 40-45 mph there is enough air passing through radiator, and enough heated coolant convection to keep engine from over heating.

Many moons ago I drove a 273 Dart 100 miles with water pump making a clicking noise (later discovered plastic impeller was in several chunks) at that magical 40-45 mph range, engine maintained normal temperature.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

If anything that engine bay is very handsome!

Hopefully wjajr is right, it's only a water pump. Sounds logical, at that speed you are getting good air through the radiator and there is very little load on the motor.

I am with a couple others....water pump.Make sure its a good one, stay away from the cheapie ones.
Good looking car too!

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Wife's: 64 Valiant
My: 70 Road Runner, 67 Barracuda, AND the 62 Valiant drag car!!

You should inspect the "new" 3 row radiator to see if it has any plugged tubes.
This can happen when the engine rebuild is done after the radiator work.
The block cleaning process can loosen / leave crap in the block, that stuff makes it's way into the radiator and clogs it up.
DD