I have a freshly built LQ4 that's built for boost that i'm having a hell of a time getting to run without overheating, so much so that after 10-15 minutes of idling it will hit temps of 230+ and start boiling over.

Here's a list of my cooling parts and part of my motor build.

Engine:
2001 LQ4 bored .030 over
Wiseco 4.03 -15cc pistons
Callies Compstar H-beams
Brutespeed blower cam
stock 317 heads with 3 angle valve job
Patriot Dual springs
GM LS9 MLS head gaskets
76mm Turbo - crossover running close to the radiator but wrapped with header wrap.

Cooling:
C&R single pass 2 row radiator
New LS1 water pump (heater core fittings plugged)
Mr Gasket 160 thermostat (6367), bleed hole at the top
CSR straight thermostat housing (modified to fit t-stat)
2 - 12" pusher fans (1600 cfm each)
2 LS6 front steam vent tubes T'd together and returned to fitting in top of water pump outlet

When filling the radiator with distilled water and water wetter, I unhooked the hoses going to both steam vent tubes until water started flowing out of each. I used a Lisle spill free funnel to help "burping" the cooling system. with the motor running I squeezed both upper and lower hoses to free as many bubbles as possible, which worked well. Everything was going good for about 10 minutes until it got to 180* on my Autometer electric temp gauge in the pass head, which is usually about 20* lower than HP Tuners via the stock temp sender in the driver head. Water level in the funnel began to rise until it started to bubble over. it's almost as if the t-stat isn't opening and the water has nowhere to go but out of the radiator. last week I pulled the t-stat and tested it by boiling it in a pan, slowly opens right around 160 and is fully open in less than a minute.

I'm at a loss right now. Does anyone have any suggestions for me.

Please let me know if I need to add details or pics.

Thanks ffor the help in advance.

Avery

 

What # radiator cap do you have? Things change and get funky when you lose pressure in a cooling system sometimes...

 

it's a 19-21 psi cap

 

What is your A/F ratio at idle? A lean ratio will create excessive heat. Vacuum leak check?

 

are you sure the water pump is turning the right direction?

you can get a clear piece of hose from home depo the same size as your radiator hose, either just a small pieces inline with a couple pieces of metal pipe for couplings with hose clamps. Or depending how long and amout of curves your upper radiator hose has in it, you can use a long piece of the clear hose. You just want to use it long enough to see the coolant/water moving from the motor to the radiator.

I suggest to take out you thermostat hook up some clear hose to see if the coolant is moving too fast or too slow..... That will tell you alot, or if your just not getting enough air flow.

 

I would guess one of two possible or a combination of the two.

Radiator is to small or has blockages
Fans are not moving enough air

Ok a third air flow thru radiator or fans is obstructed.

You can use an inferred temp gun to check various spots on your radiator to make sure it doesn't have any blockages.

You can also use the temp gun to check temps around the heads, if you have a hot spot it could be an air bubble.

If the voltage is low to the fans they will run slow.



Good luck

 

my car pushes the coolant out if i let it run too long with the cap off. i think its because its not flowing through the rad fast enough and gushes out. are you over heating when driving? i have had to fit a pair of the derale 16925 pushers to mine to stop it overheating. they are beasty fans but need LOTS of current

dont forget without the cap the water is going to boil at 212f

 

Is all the air pockets out? We remove the top hose from the rad when we "think" it's full and hold that hose up higher and fill it then carefully put back on the rad and try again. We had the problem your talking about and this fixed it. Guess its worth a try...?

 

First thing I thought of as well. It always takes me a couple tries to get all the air out of an LS.

 

I didn't log this but every time I peeked in the car to see the water temp, afr's were in the 13.5 to 14.5 range

running the standard belt routing for a c5 vette, so with the motor rotating clockwise, the WP rotates counter clockwise.

the top hose shouldn't be that hard to add some clear tubing, but the lower might be a little difficult. i'll try and give this a shot too

rad is not blocked, I've flushed it before installing to make sure there was no build up.

it's possible the fans may not be moving enough air, but even idling for 10-15 minutes in 40* weather I wouldn't think the lack of air movement would be this pronounced. I could be wrong though.

i'll check the voltage and see how that looks.

I've only driven it once, less than 5 miles to the gas station and back and yes it got close to 250*. Never got on it and stayed below 2500 rpms, maybe a max of 40 mph.

I guess i'm not able to confirm eliminating all the air pockets. I've been trying to eliminate them by using the Lisle spill free funnel. i'll try jacking it up more and filling the motor through the WP outlet hose

thanks. i'll keep on keepin on and report back

 

there was something on the YB about blocking the heater outlets
was it an LS style thermostat-they have that 2nd valve that closes off I think one of the heater fittings so water car recirculate-I don't remember the whole deal with them

 

Been having a similar problem. A guy suggested better fans. I have not had time or money to investigate further. Curious to see what you find. Mine cools after driving though.

 

Mine overheated a couple of times until I filled it through the top hose on the w/p. Really no other way for all that air in the block to find a way out if the radiator is full and blocking the only escape route.

 

Make sure you dident flip the headgaskets. I had heads and cam 04 corvette built by the owner that ran hot at idle. I have a force filler/bleeder. One thing that tip me off was the steam vent in the back of the head was dry. I pulled the heads and bam the head gasket where backwards. These where gm mls also.

 

If you are running a factory water pump and thermostat , and you plug the heater hose connections instead of looping them, you are creating this problem.
look close at the thermostat location in the water pump , it cannot 'see' hot coolant with the heater hoses blocked until the engine is already too hot. This causes it to overheat. The thermostat needs the looped flow from the heater hoses to 'see' engine heat, in order for it to open

 

X2! This is what I have done as well. This was my next suggestion

 

If you don't have the heater hoses looped that will cause it. One thing no one mention is Harmonic balancer! I have a under drive balancer25% on my engine, and it cause the water pump to turn to slow at idle, water is not moving much at idle. Once I give it gas temp drops right away! I just don't let it idle much, and if I get stopped for a while I just rev it to 1800, until I get rolling!

 

The stock thermostat bypasses when closed. I have two stock ones. One has 4 .100" holes for bypass, the other has steps where it meets the housing in the back to allow bypass.



Might have a look at your thermostat setup. Sounds funky with the modified housing you are using???

I just plugged my heater hose outlets. Today. As a safety measure, I drilled an additional hole in the WP housing for more bypass.

Would be very interesting to see what the heater valve actually looks like. If the hoses really must be looped, that valve must create a loop when the heater is off.

It's an interesting deal, others have reported no issues with the outlets blocked off. I guess I'll find out in about 3 months....when my car runs.

Ron

 

Water coming out of the radiator when hot can be caused by the water expanding when it gets hot.

To properly check you need to keep the cap on and see if it pulls coolant from the expansion/overflow tank as it cools down.

 

I don't believe the oem thermostat bypasses much when closed, as you have to compress the 'bypass' valve's spring in order to seat the thermostat, which effectively restricts the bypass.