So I had the motor and tranny fully rebuilt on my dart. All new everything. A shop did it. I picked it up yesterday and drove about 5 miles and it started to overheat very quickly. I pulled over and it was bubbling out of the radiator cap. I tightened all of the hoses, bought a new cap and its still doing it. Both fans are working. It wants to overheat super quick. Pretty much new 3 core radiator in it. New water pump.

Motor was just rebuilt and everything in and in it is new. No expense spared. I'm taking it back to the shop on Monday to have them sort it out but if you guys could point me in a good direction and I could learn something in the process that would be awesome.

Let me know if I can supply more info.

Check the thermostat.

Richard

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Part of Tyrde-Browne Racing

X2 on the thermostat. Maybe it's backwards? If so then the upper hose near the thermostat would be the last place to get hot so feel the hose there to check. Dennis

Inspect the tops of the radiator core tubes for debris.
If the rebuilt engine block was "tanked" but not well rinsed, a lot of rust scale can get loosened & "deposited" in the radiator, upon initial start-up.
DD

K I thought about it being the thermostat too but I know they put a new one in. Would it be bad to run the car without a thermostat to see if that's the problem with it overheating so quickly? And I ran it with the radiator cap off to see if any bubbles came up and none did. Is that where I would see the debris as well?

Thank you guys for your help. Sucks when you pay an assload of money and it's all pretty but won't go anywhere! I will say this is my 3rd slant 6 and the first rebuilt one and it's so tight and powerful. I'm really excited about it.

Would it be possible that it's a bad water pump?

No, it can be ran without the thermostat... and I am guessing either it is faulty (if new one ) or as someone else stated installed backwards..

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MRO....

Cheap, Fast, Reliable.... Pick 2...

They may have put a new thermostat in but did they install it properly ? It can be installed backwards easily if you don't pay attention.

Also, with some of the cheap crap on the market these days, I know more than one person who got a bad one off the shelf.

Yes, you could remove it and run it to see if that was the problem but I wouldn't leave it like that. If that is it, put a new one in. Don't continue to drive it like that. Dennis

While you have the thermostat out and before you top off the water look into the radiator to see if there is any crud blocking off part of the tubes as Doc suggested.

Richard

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Part of Tyrde-Browne Racing

Thanks buddys! I'll post an update tomorrow!

There's a baby crack in the radiator! Underneath the cap! Just found it. Would a baby crack make it overheat badly? Jb weld?

Since its a new rebuild, check the obvious things like timing advanced too much or carb lean, those things can make one heat up fast. Also make sure its full of water and doesn't have an air pocket in the block or head preventing it to fully be filled with water.

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There's no such thing as too much cam....only not enough engine!

If the engine begins to overheat, try turning the heater on full blast- hi blower, max heat, windows down. If it pumps out lots of HOT air then that would indicate that the water pump works adequately (& that you have flow problems thru the rad for some reason). If it blows cool, then you might have "bad" water pump, clogged heater core, or possible "air"-bound core (maybe caused by headgasket- combustion sealing problem)

But, If the shop didn't do something right, bring back to them & have them figure it out & fix it. I'd have called them 5 min after it first acted up & towed it back that same day.

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63 Valiant Wagon
225 - 4 bbl

Awesome. Thanks for the info I'll try all of that tomorrow. I called them right when it happened and they told me to bring it back. But theyd have it over the weekend just sitting there so I kept it for the weekend and am going to tinker on it. I figure with your guys brains I could learn something new before I take it back. It's my first ever rebuilt motor so Id like to learn as much as possible while I still can. Definitely need a manual though.

Thank you again.

If that crack in the radiator doesn't allow it to build up pressure, then yes, it could cause your problem. The pressure in the cooling system raises the boiling point of the system by about 45 degrees thus reducing your cooling efficiency.

I checked the coolant in my daily driver some time back(it has a plastic reservoir and cap) and topped it off. After that, my car would overheat every time I drove it. Didn't really put the two together but after much investigating I realized that I wasn't screwing the cap down all the way so it wasn't building up pressure (your crack). Dennis