240sx coolant boil problem

[damienknight]

I have a 1990 240sx automatic. I have the stock KA24E engine in it. I'm going to convert it to manual, but first I need to figure out how to fix my damn problem. Here's the deal:

When I drive it around, the coolant will overflow in to the reservoir and start to boil. I've alread tried flushing the coolant system, and when I refilled it the radiator only took 4 quarts of fluid, instead of the specified 7 1/4 quarts. I tried running the engine with the cap off to see if there was air in the system, and the coolant started overflowing from the radiator after idling for less than a minute.

I'm just looking for advice as to what steps to take next, if anyone's had this problem that would be great. I'm afraid it might be the head gasket, but I want to try other things first, thanks.

[navysnail]

it sounds like the head gasket

did you bleed the coolant when you refilled it ( bleed plug on intake manifold)

[damienknight]

yeah, i bled the block

[navysnail]

if it boils after startup, then its gona be your headgasket because the water is still cold. check your compression

[black s13]

change your thermostat, or just take it out like i did..

[CiPHeR_Tx]

even if you bled the system...you might still have an air pocket in the water pump housing...which means no water flow. i had the same problem after i swapped out my radiator, water pump and thermostat....almost forgot...radiator cap could also be the problem...if the spring or seal is bad...the hot water can flow freely into the overflow

[navysnail]

is it accually overheating or is the boiling caused by air shooting into the coolant from a blown head gasket

[damienknight]

it isn't overheating. and it could be a blown head gasket, that's what i'm trying to figure out. the thermostat's been replaced and coolant's been flushed...

[CiPHeR_Tx]

try changin the radiator cap

[damienknight]

yeah, i just ordered one online. i'll do that as soon as it gets here.

[navysnail]

does it "boil" when you first start the car, even when its cold. if it does, its your head gasket

[damienknight]

it usually take about 5 or ten minutes.

[CiPHeR_Tx]

i've had the same problem because of a radiator cap...you'd be suprised at how much those do

[navysnail]

yep, radiator cap is very improtant, it effectively raises the boiling point of water from 212 to about 260 due to the fact that it puts it under 14psi.

[SR20S14]

I wanted to know that fi u take out the thermostat comepleely does that change nething and if u tak it out is it bad to run ur car without one?

[navysnail]

it is ok to remove the thermostat, but it will take the car a long time to warm up and it will be in warm up mode longer

[damienknight]

OK, I tried running it with a new radiator cap, same problem. I popped the hood after I was done running it, and I could watch the coolant surging into the reservoir.

[navysnail]

it rellly sounds like a blown head gasket, have it compression checked. if your compression is low on any 2 adjacent cylinders, then its probobly the gasket

[damienknight]

i don't know if this helps at all, but i noticed a hissing sound when the coolant was boiling. i'm gonna go get my compression tested next week.

[i2ice4m3]

If it were the headgasket, some symptoms are white smoke from the tailpipe, oil/coolant mixed in either the crankcase or radiator.

4 and 7 quarts is a huge difference. Did you fill it correctly? the 7 quart coolant capacity is for the entire cooling system. maybe you just filled the radiator?

radiator cap? if the seal is bad, the water will just spill over all the time.

[damienknight]

According to the manual, the radiator holds 7 1/4 quarts of fluid and the coolant reservoir holds 3/4 to the max fill line. those are the only two places I know to put coolant. and as far as I know, I filled it correctly. I got a new radiator cap anyway, just to eliminate that problem. I'm gonna compression test anyway, just to rule out head gasket. Any chance a clogged radiator wouldn't overheat? or maybe a broken water pump?

[Dattebayo]

the only way to test for sure if its the head gasket is to check the coolant for Hydrocarbons. They have a kind of sniffer for this at most garages. Also, you should notice white smoke coming out of the tailpipe if so. (white smoke = coolant, bluish smoke = oil)

[i2ice4m3]

According to the manual, the radiator holds 7 1/4 quarts of fluid and the coolant reservoir holds 3/4 to the max fill line. those are the only two places I know to put coolant. and as far as I know, I filled it correctly. I got a new radiator cap anyway, just to eliminate that problem. I'm gonna compression test anyway, just to rule out head gasket. Any chance a clogged radiator wouldn't overheat? or maybe a broken water pump?

well the coolant circulates through the engine...so that must be part of the capacity. anyway...a clogged radiator or broken water pump are definite candidates. usually water pumps just leak when they're done...which will leak the coolant unnoticeably initially. clogged radiator means less heat exchange going on. well...good luck w/ ur problem. :aug2

[lost93]

running with out a thermostat lets the engine heat up quickly and makes it hard to keep it cool due to the fact theres nothing to slow the coolant down to let the radiator do its job.

[Chingon]

how 'bout just doing a comp. test to eliminate the possiblility? 5-10 mins, and that doubt is out the window.

[black s13]

running with out a thermostat lets the engine heat up quickly and makes it hard to keep it cool due to the fact theres nothing to slow the coolant down to let the radiator do its job.

you have it completely backwards. the thermostat doesnt help the radiator, it impairs the flow. without a thermostat, in hot weather, my car never gets over 150 degrees. in the winter it never went past 105, which means no heat. my head is cracked, so i cant run a thermo, however i would have one if i could.

[lost93]

yes but the coolant is moving so quickly it does not have time to cool . if your car ever gets hot. i don't know why your car don't overheat with out one.

[Chingon]

actually, a thermostat is there for a reason....and that is to help the car warm up when cold (or when barely starting up). This means that if you have water going through the system, the car will have a harder time reaching operating temperature and warming up the oil. Also i'm not sure if the thermo. closes again in the highway or not. Anyways, you don't want your car too cold and you sure as hell want to have a thermostat in your car.

[SRdave240]

A good alternative to running w/o a thermostat is to drill a couple of holes thru the body of the thermostat. This will increase the flow a little w/o making the coolant flow so fast that it doesn't have a chance to cool thru the radiator. It will also keep your car from taking a long tiome to get up to temp.

[black s13]

wow, you guys are insane, the coolant defenitly isnt flowing too fast to cool down. i run with no thermostat and no fan, and even on 100 degree days, sitting traffic it wont go over 180. if im moving it sits right at 150. with a thermo it was right at 180 all the time.

a thermostat is just a spring that expands and contracts with heat, its constantly changing, keeping the coolant at the same temp (usually around 180) with no thermo the coolant doesnt get slowed down, so doesnt heat up as much in the block.