Strange over heating

stiguy · #1 03-21-2014, 07:18 AM

Okay so I've been dealing with a over heating problem and it doesn't matter if it's 30 or 90 outside. I drive 15miles to work one way half on side streets and the rest on the fwy. And it will try to over heat on both.

What it does is after driving for prob 20 min and it's all heated up if the rpm don't stay high it will start to overheat. So say I'm at a light and I see the temp climbing I have to rev the engine above 3500 then the temp will come down. Same thing happens right when I get off the fwy :/ I have noticed that if I start slowing down before my exit and downshift early it does seem to help it not overheat as fast.

I changed the thermostat didn't change a thing. Changed the water pump last week didn't change a thing. Tried flushing the system didn't help. Tested the fluid for a headgasket leak a few times all came back negitive. I did blow the cooling hose under the manifold last week.

So wondering if there is a build up of pressure? Maybe a plugged radiator? It looks clean tho.

Any ideas? Thx guys

1986nate · #2 03-21-2014, 05:31 PM

make sure you get all of the air out of the system?
Also, many times head gasket failures won't set off the various tests on EG/EJs especially if you're only doing them at idle and no load. What typically happens is one of two things, coolant is leaked into the combustion chamber burning off ever so slowly and in turn, combustion gases are leaking into the coolant heating it up. This will only happen at higher loads and RPM, then once the engine slows down, the water pump slows, pressure drops and you get flash boiling.

Tapani · #3 03-21-2014, 10:17 PM

See my post #13 in this thread:

http://www.subaru-svx.net/forum/showthread.php?t=58585

As Nate said, you need to load the engine for the test.

/T

stiguy · #4 03-21-2014, 11:34 PM

Quote:

Originally Posted by Tapani

See my post #13 in this thread:

http://www.subaru-svx.net/forum/showthread.php?t=58585

As Nate said, you need to load the engine for the test.

/T

Yeah I've tested it right as its been overheating like pulled over put a rag over the rad cap opened it up and tested it. Stayed blue the whole time.

Tapani · #5 03-22-2014, 03:02 AM

You may still want to double check. When it's not spitting coolant, i.e. before it over heats.

Just make a few full throttle spurts and then quickly to the test. You want to detect the gas bubbles from the gasket leak - not the steam bubbles from the flash boiling.

Just an idea and costs nothing if yo have the kit.

/T

stiguy · #6 03-22-2014, 04:30 AM

Quote:

Originally Posted by Tapani

You may still want to double check. When it's not spitting coolant, i.e. before it over heats.

Just make a few full throttle spurts and then quickly to the test. You want to detect the gas bubbles from the gasket leak - not the steam bubbles from the flash boiling.

Just an idea and costs nothing if yo have the kit.

/T

Okay got it I will try that out and report back thanks

1986nate · #7 03-22-2014, 06:54 AM

Are you having to add coolant after any of these drives? (once the car cools down)

(I'm guessing yes)

stiguy · #8 03-22-2014, 01:37 PM

No I don't have to it doesn't go down

1986nate · #9 03-22-2014, 01:47 PM

Quote:

Originally Posted by stiguy

No I don't have to it doesn't go down

sounds like you have air trapped in the system then. How are you bleeding it?

stiguy · #10 03-22-2014, 02:31 PM

I park it up hill fill it run it with the cap off until I see the water moving and then top it off and put the cap back on and fill the res

1986nate · #11 03-22-2014, 02:35 PM

Quote:

Originally Posted by stiguy

I park it up hill fill it run it with the cap off until I see the water moving and then top it off and put the cap back on and fill the res

do you have the heat set to the highest temperature setting as well and do you run it until the cooling fans come on?

stiguy · #12 03-22-2014, 03:21 PM

Actually no to the heater didn't think of that. And yes to the cooling fans

1986nate · #13 03-22-2014, 03:39 PM

Quote:

Originally Posted by stiguy

Actually no to the heater didn't think of that. And yes to the cooling fans

be sure to turn the heater on when you bleed. It may or may not be the issue, but worth a shot. If you're not losing coolant, then sounds like there is just air trapped.

stiguy · #14 03-22-2014, 06:58 PM

Yeah but you'd think that after like a month of driving it without opening the system it would have worked itself out... :/

Chucksta · #15 03-22-2014, 11:47 PM

Ideas? Yes!... Answers?.. No!

There's some definite weirdness in the problem. As noted, if it's a head gasket problem, anything I write after this point has absolutely no worth at all.

I've had a temp sensor go bad... mine made my dash gauge read way low, when in fact it wasn't.. could it be possible that they can also malfunction and read to high? I don't know the answer to that one. The other side of that coin is that revving the engine brings the reading down. Revving the engine does two things, burns more gas ( more heat generated ) and spins the water pump faster and pushes the coolant harder. Then the gauge goes down.. Do you have the hardware and software necessary to read the coolant temperature from the ECU coolant temperature sensor?

You blew the coolant hose under the manifold.. In your opinion, was it ripe and ready to go, or, if it was in good shape, why didn't the rad cap vent the pressure?

You changed the thermostat.. I did too.. then found out that the bleeder / bypass nipple has to be facing up. If it's not, it can make getting all the air out of the system almost impossible. ( tip of the hat to previous posters on this thread).

Maybe a plugged rad? You flushed it, right? Was it a chemical flush, designed to remove rust, scale and build up? If so, did you see any evidence of unwanted material come out? That it looks clean can be misleading, any buildup inside the tubes acts like a blanket that stops heat transfer, and restricts flow. Did you mix the anti freeze with tap water? I was advised that this was important... it should only be mixed with distilled water. and that Subaru Anti-freeze is recommended. As near as I could find out, Zerex pink ( also refered to as Zerex Asian), is either very close, or identical.

The issue presents itself as a slow overheat.. with increased pump speed being the temporary solution. Just for an experiment, try turning on the defroster on high as the temp climbs. The heater core is nothing more than a miniature radiator. The air should come out of the vents smoking hot, and, if the temp rise is not as dramatic as usual, it points a finger at the rad as being the culprit. Not definitive, but indicative. If, with low revs, the defrost duct air temperature drops, it points to, for whatever reason, the coolant not circulating properly. From the best I can wrap my head around an SVX cooling system, flow through the block and flow through the rad are two different beasts. A restricted rad would result in more coolant coming back through the pump from the bypass line.

Also, from what I can glean about the SVX cooling system, it's meant to have a fairly high flow. This means (to me) that there shouldn't be a high drop in temperature between the coolant temperature between the rad intake and the water pump intake. If you have any way of measuring the temp difference, it would be interesting to see what the temperature drop is. An infra red thermometer would tell you what the drop is at various RPM. Eg: a small drop in temp at idle would show that the flow is fast ( which is fine) OR that not much heat is being extracted, or something in between. A small temperature drop at higher RPM would indicate the exact same thing. What you'd be looking for would be that the temperature change would be linear relative to RPM. The larger the drop in coolant temperature at the idle compared to the drop at higher RPM would seem to point to a restricted rad. The air temperature from the fans would be the last part of this very objective observational test. If the air being pulled at idle is ... say 120 F, and then quickly climbs to 150 F when the engine is revved, it would seem to indicate restrictive flow. If there really isn't much of a difference in air flow temperature, it would seem to more point to adequate flow, but insufficient thermal transfer. ( radiator tube scaling restricting heat transfer).

I know exactly what I meant to say there, but have severe doubts that I expressed it properly, in a manner that makes sense. If you don't think that last paragraph made sense, or can't figure out what I think I meant to say... just ignore it

Keep in mind, that most of my automotive training came from when cars had carburetors and point ignition.. If someone says "don't listen to him".. Listen to them... I will take no offense..None at all.