Well I finished my lq9 swap 390ci, and my car is overheating bad! I don't get it... I drove it for months and it was fine, then one day it over heated and luckly I caught it before it got to bad and shut the car off and costed to the side of the road. There was coolant spit up all over my engine bay. I first tried a thermostate, replaced it started filling up my car with coolant and noticed my radiator was leaking, so I got a new radiator. Well then I start it let it run, seems fine figured it was fixed, walked away for a second and my car dies. I look at the temp gauge and it was at 260... Now I'm just stumped. I checked my lower radiator hose and it was cold and so was my entire radiator. Thought I bought a bad thermostat so I bought a new one started it, still does it. I'm really stumped... Can anyone help? It's not smoking any, my oil looks perfect, and my radiator is not bubbling at the cap while running so I'm pretty sure its not a head gasket... Does anyone have any ideas?

 

Try taking the thermostat out and fire the car up....you should be able to see/ feel the coolant flowing freely through the system....I've never seen an ls water pump go out, but I'm sure it can and does happen....if your not getting and flow without the thermostat in then I'd try replacing the water pump

 

Thanks il go try it right now and report back. Not sure why i didn't think to try that...

 

Sounds like trapped air in the system. Loosen the coolant crossover lines until you get a good flow of coolant from each one. With air in the system it will heat up fairly quick. Good luck.

 

Water pump is flowing and I thought the same about the air... But I took off the steam por which looked to be the highest point in the system and its flowing out of it... Or is the steam port not sufficient enough

 

just curious if youve tried a new radiator cap? or have had yours tested?

 

Did you loosen both sides?

 

No I never tried a radiator cap... Maybe that's my problem? I just got a new one when I swaped my engine but its an advance auto one so maybe that's it...

 

No just the one that flows out and into the house, the driver side one.

 

The 5.3 in my mustang if i did not use my funnel to get the air bubbles out it would over heat every time but if you have a big funnel put it in your radiator make sure you have a tight fit arround the radiator opening and fill the funnel up to the brim and let ur car run and let watch the bubbles come to the top when it stops bubbing put ur radiator cap on and go for a test drive.. every once in a while i would suck in air somewhere and i would have to bleed it out hope it helps!!

 

I was just filling it without a funnel I don't have access to one right now but I was topping off the fluid while it ran. I'm going to take it to my work and try to use this thing we have. U put it on the cap opening and hook it to compressed air and it puts a vacum on the coolant system and you can watch the hoses shrink from it. Then it sucks all the coolant in real fast. Il probably buy s cap to just to rule that out.

 

Did you rebuild this engine? Were the heads off?

 

Yeah I built it from the shortblock up, I'm pretty sure its not a headgasket though. I could do a compression test on it if all else fails...

 

You probably had that radiator leak for awhile. It was probably so small a couple weeks ago that it only spit coolant out after you shut it down and walked away from it when temps and pressures RISE for about 30 minutes after shutdown. Then when it cooled down it sucked air in. Then when that air space in the system go to the breaking point...you overheated.

Now....you have air in the system. If the lower hose and radiator were cool and you overheated...the -t-stat never opened because there's an air bubble on the engine side of the t-stat.

Do this...works every time: Might take a couple tries though.....just keep an eye on the temp gauge so you don't overheat while doing it.

**Bleeding the system of air:
Take the radiator cap off when its COLD, top it off, start it up and let it idle, and let it warm up till the t-stat opens. I rapidly squeeze the upper and lower radiator hose like 20 times each while its warming up to help move any air bubbles through the system and by the t-stat on the engine side. When the t-stat opens you’ll see the level drop as you squeeze the hoses, its sucking the coolant through the system. You will also see the coolant start to flow in the radiator fill neck, once it starts to flow the level should drop down a lot, IMMEDIATELY top it off with coolant/water. Then the flow will stop when the t-stat closes. Wait one more time for the t-stat to open again and start to flow, if it drops down again top it off again. Do it a 3rd time if you want to make sure. When the level does NOT drop down when the t-stat opens and coolant is flowing....you're system is free of air bubbles. I always squeeze the upper hose during the whole process to keep any air bubbles moving through. Always works like a charm. Just keep checking your temp gauge until the t-stat opens for the first time to make sure it’s not sitting there overheating from a trapped bubble. May take 10-15 minutes for the t-stat to open the first time.
If you do start to get hot while sitting there and the t-stat will not open…..you have a good sized air bubble on the engine side of the t-stat. Shut the engine off and rapidly squeeze the upper and lower radiator hoses again. Then start the engine again and see if the t-stat will open. Sometimes you just have to work those hoses to move the air through. Even after it seems topped off after a couple cycles…check it the next time you have a cold engine…top off if needed.

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Couldent I just put a vacum on it and do the same thing with no thermostat in? Then put the thermostat back in and hope the air bubble is gone from inside the block?

 

I've seen people leave a paper towel, tools and loose nuts and bolts in an engine before believe it or not.

If your water pump is working and you're getting flow up top but not through the radiator, there could be something clogged in there somewhere.

Are you sure there isn't a paper towel stuffed in the water jacket around one of the cylinders somewhere or in the water pump hole? Maybe in one of the heads?

Just trying to think outside of the box since you've gone through everything else.

 

I'm positive, I was very **** about that and its been fine for months untill now...

 

A radiator cap will not cause the problem of no flow..........
Did you try filling with the ft end of the car jacked up?

 

No that's what I'm gonna try to do though, I think I have an air pocket.

 

you said you pulled the line off he crossover and were is this connected to the system?

Is the heater hose looped or hooked up?

Tim