Rebuilt Chevy 400 Coolant Surging Problem

[corey6969]

Hey guys,

I finally got my engine built, its a small block 400 bored .030 over. I am having a problem with the coolant surging and kinda seems like its boiling. Weird thing is both temp sensors say the coolant is no more then 190 degrees when its bubbling. I have one sensor in the intake(had fuel injection on it for a while) and one in the driver side head. Stock guage shows straight up in normal and the computer showed 180-195.

Is it possible that block couldnt take the .030 over and its creating hot spots. I have heard that some 400 blocks cant take an overbore or you should sonic test(??) the cylinder walls before boring, not sure about that last one. I used the 400 head gaskets and did check before i bolted the heads on that the steam holes lined up.

I have had the heads off before i rebuilt the engine, the only thing I did different this time was put in the coolant restricter metal things in the intake gasket. I thought it might help my carb fuel boil when the engine turns off. I even poked around with an infrared temp gun and the temp shows the same as the sensors to. It will even start to surge like that when you just first start it up cold and let it warm up. The heater hose even moves up and down a little by it self

Any ideas??

Other then that it runs good and has tons of power. Ive ran it like that for about 700 miles now.

 

[Hogback Fabrication]

Bubbling coolant can often mean a blown head gasket, though its usually accompanied by overheating.

 

[Jason4x4]

How are the heater hoses hooked up?

one to radiator and one to w/p or intake?

If one is to intake, and one is to w/p, it might be possible to do that, but I'm not sure.

 

[corey6969]

How are the heater hoses hooked up?

one to radiator and one to w/p or intake?

If one is to intake, and one is to w/p, it might be possible to do that, but I'm not sure.

One goes to the radiator and one goes to the intake

 

[mike in mo]

did you have the heads checked for cracks 400 heads are thin cast and bad about cracking. any anitfreeze lost?

 

[fried_guy]

I just got my 400 + .030" running last night. Is there a specific spot you think the boiling is happening? Did your lower radiator hose collapse under the vacuum from the water pump (happened to my last engine)?

 

[ramjet gmc]

sorry but i cant offer any teck info -- but would a electrical waterpump offer more flow -- would help cool down

 

[corey6969]

did you have the heads checked for cracks 400 heads are thin cast and bad about cracking. any anitfreeze lost?

I had the heads redone about 40000 miles ago so i didnt have them redone again when i rebuilt it. I dont know if they checked them at that time. Not sure on lost antifreeze i dropped the old stuff out and put in some new john deere stuff. Theres no external leaks so Ill try and keep track.

I dont believe its sucking it back in from the recovery tank either and it did do that before I rebuilt the engine.

 

[corey6969]

I just got my 400 + .030" running last night. Is there a specific spot you think the boiling is happening? Did your lower radiator hose collapse under the vacuum from the water pump (happened to my last engine)?

I cant find my infrared temp gun so I havent been able to see if I can find a hotspot. I put on brand new hoses and mine didnt collapse. I didnt realize the new hoses didnt come with springs anymore, shows how old mine was.

 

[GNERGY]

Change the radiator cap if it isn't sucking it back from the overflow tank.
Tarey

 

[corey6969]

I put one of those radiator caps with the temp guage in it and it shows the water never gets above 140 so i would assume the radiator is good to go, anyone have any other ideas on the coolant surging(kinda like its overheating). It isnt overheating just sounds like it is.