So im loosing coolant in my 95 4runner. Probably about 2L every 150kms maybe? Always topping up my rad. Cant figure out where its going. Did a pressure test at work today, held up great no pressure drops. If it was leaking that much I would of noticed it by now. All I can really think is a blown headgasket but I dont smell coolant being burned and I dont smoke white. Any way to tell if my HG is done? Took a look at it while I was doing the pressure test and I dont see any seepage. Pretty stumped. Any help would be appreciated.

 

Well the fact that your pressure test turned out ok would lead me to think the HG is fine... USUALLY you see a drop in pressure in the cylinder nearest where it failed.. any chocolate shake in the oil?

 

The best way to check the head gasket is to do a compression test on the engine. Also if it's an automatic trans check the fluid in there. If the cooler in the rad goes you'll lose coolant into the transmission.

 

I did a coolant pressure test if you mistaked that for a compression test Spazz, Im going to do a compression test on it now. If that turns out good im going to go ahead and suspect its my heatercore. Lost heat earlier today for a bit, engine temp went up then the heat randomly came back then the temp dropped to normal again. Rad was full. I hear the coolant wooshing around in the dash which makes me believe its the heatercore. But if the heatercore was leaking wouldnt my floor be soaked?

 

Check for hydrocarbons in the coolant. You can get a test kit at most auto parts stores.

Sounds like the headgasket is failing and allowing exhaust gasses into the coolant system. When enough 'air' builds up around the thermostat, it will no longer open since air can't transfer enough heat. This in turn causes the coolant to overheat and spit out of the overflow. It will also cause the heater to stop putting out hot air due to the stopped waterflow.

 

Sounds like an air pocket in the heater core due to the coolant being low or not being bled properly when you refilled it. You may want to try a block tester to check for exhaust gasses in the radiator. Also, when you do the compression test, try to take a look at the tops of the pistons with a flashlight. If 1 or 2 of them are nice and clean, you're burning coolant.

 

Beat me to it! I type slow!

 

Ahh.. Gotcha.. Yep I thought you were talking a compression test. My bad. I think these guys are on the right track with the advice.

 

Well, just did a compression test. My motor has 250kms (155miles) and it came out great.

cyl 1 - 183psi
cyl 2 - 178psi
cyl 3 - 182psi
cyl 4 - 172psi
cyl 5 - 179psi
cyl 6 - 185psi

as you can see those are excellent numbers, I think ive determined its not my head gasket, what do you guys think?

 

The water bypass tube under the lower manifold between the heads may be leaking filling the valley with coolant.

3.0 coolant leak from bypass tube

 

The pressure test would have revealed any leaks.


Hard to say...water pump could be cavitating, water pump bearings could be failing, timing belt tension could be loose, etc., etc.. If the heater core and/or radiator were clogged, I don't think it would be intermittent. With those compression numbers, I think it's also unlikely it's a cracked head or failing headgasket.

Edit - after it starts to overheat, is there anything coming out of the overflow?

 

If no leaks as determined by the pressure test, where is the losing 2 liters of coolant every 150 km stated in first post? There is a leak or burning of coolant someplace in that engine that the pressure test failed to detect.

'scribing to see what the fix ends up being.

 

One example that comes to mind is a water flow issue as I mentioned above. What happens when water flow slows/stops? Overheats and and spits the expanding coolant out of the overflow. If the temp returned to normal before the OP stopped, he wouldn't have noticed coolant coming from the overflow. The heater also stops working when water flow stops, and that was one of his symptoms. That's not the case with a simple coolant leak.


Could also be a bad radiator cap. Or as simple as a thermostat (sticking and/or no air bypass). The absolute first thing I would do is check the rad cap test the thermostat. Drill a 1/8" hole in the outer ring of the thermostat and position it at 12 o'clock when reinstalling...I bet that fixes it.

 

just a ? if it is the head gasket would there be a difference in the way it runs ? and is there a way to check the head gasket without a compression test .do not have a tester or $ to get one, and the only advanced auto is about 30 miles away .

 

This is interesting.. I just did my HG's because it was eating coolant though i only found a little milkshake under the oil cap but that was it. Anyway after it it still eats a bit but not very much. I can drive it for atleast 2 months and not top the rad up. But still it shouldnt eat any. Im going to get a mew rad cap and after that maybe try the hole in the t-stat thing.

Good luck man!

 

Good points. Suppose it could be a simple crack in the overflow tank too. One would think that much coolant would fly back and hit something hit and smell, but maybe not.

 

Smell is a very good indicator. Nine times out of ten you can smell the antifreeze as it spews while driving.

 

Tried a new rad cap and it didn't work. I think the next thing im going to do is drain the cooling system and fill it and try and bleed it properly. I should probably check my thermostat before I do that though.

 

Maybe take out the overfolw tank and give it a good looking over and also the hose from the top of the radiator to the tank?

 

well, put a new thermostat in and tried to bleed the cooling system.

Overheated on me again today, added like 5L of coolant can still hear water rushing through the dash and it feels like im loosing a bit of power untill 3000rpms then it picks up and goes.

Im almost certain at this point its my head gaskets. Anything else I should check? And how can I for sure confirm its my headgaskets before I get into the job?