Well, with my own and all the other overheating posts I've seen lately i wanted to delve into something that i found to be my issue...The water pump it's self. This is an older "poor mans" test that was used for checking older Chevy v8 water pumps when they would have the same issue.
You see, some will blame the radiator, but when your just cruising and have the stock cooling system (complete with OEM fans) you should never overheat even with the AC on, i don't care how built the engine is. this is because heat is a form of energy transfer from the energy created in combustion... but when you're off boost an not making much power (or energy) the stock system should be more than ample, but if it's not doing the job under daily driving then you have an issue (duhh) but as far as big aluminum radiators and such, they are not needed unless your road racing or running the car for long periods under high power (making more energy dispersed heat than the system was designed for for prolonged times)
the thing is a perfectly good/new reman or aftermarket water pump can cause you to overheat even though nothing "seems" wrong with it and you just put it on
Here's the deal....The tolerances of impeller to housing and the impeller shape and angle of fins on some pumps are not the same as OEM therefore they start to suffer from suction loss on the side they pull the coolant into themselves on. This causes poor circulation and many other things (similar to when an oil pump gets too much clearance and goes bad)...there's only one way i know how to test this but it's a pita, and ill explain in a minute.
But first off, I wish i wasn't packed up and had a camera to get some pics to show you but i compared an OEM to "reman" pump and saw enough differences to convince me to test mine for flow other than just function and found my issue
What you need:
4 hose clamps the size of the heater lines
some radiator hose and 2 pieces of solid tubbing to extend your heat lines
2liter bottle, (clear)
some wire for hanging bottle
a good thermometer that will reach 200+*
How to test:
First this is messy!
you need to take BOTH heater core hoses off and run them outside the car with some extension tubing from autozone..then cut the top out of a 2 liter bottle big enough to put both hoses in and find a way to elevate it to the height of the engine or a tad higher (make sure that both lines stay submerged in water/antifreeze (you may even want to put some water in the jug before starting the car to avoid pulling in an air bubble)
At this point you want to plug your radiator overflow hose as well because if pressure builds that's a whole other issue
Now, with both hoses in the suspended 2 liter bottle, start the car and start warming it up... the coolant will flow from the "out" heater line into the bottle and the pump SHOULD suck it up with the other hose thus giving you an un-pressurized but flowing cooling system
Now as coolant expands of course the bottle might overfill (no worries, dump some off)
What you want to do is.
A.) look for bubbles to start forming while measuring temps of the fluid... bubbles mean it's boiling and this shouldn't happen to at around 180* or so, if it happen earlier the pump probably isn't flowing right, or there could be a head gasket leak letting hot gasses ito the system, this would be accompanied with a lot of extra bubbling in the coolant as well.
B.) make sure that the pump is sucking out the same volume of fluid from the 2 liter that it's pumping into it.(within reason, a slight difference isn't bad, but i do mean SLIGHT). if it's boiling earlier from the reading at the bottle (not the gauge ) or it it's not keeping up with sucking the fluid out as fast as it's going in, well, your pump is not working very well and needs replaced (even if it's new it's no good...fact)
Now since the overflow is plugged and we have an "open in/out" bottle we shouldn't have pressure (this is why the coolant should boil also) if your upper radiator hose is pressurized then you likely have a clogged cooling system that needs flushed and possibly a blown head gasket depending on the bubbles and temperature of the boil
If you suspect a HG just rent or buy a leak down tester and that will tell you FAST if you have a HG issue... in fact with the Rad cap off you can usually hear/see the system bubble with the car off and pressure in the blown cylinder.
this water pump flow issue is a little known, but probably more common cause then you would think when you're driving and everything is cool until you climb a slight hill, accelerate in traffic and so forth but not using any or much boost. a bad HG will push coolant under higher boosts and that's different.
I'm feeling sick today so if i think of more I'll add it on here, but now i know i have a water pump job ahead of me and I'm not buying another reman or aftermarket pump again, I'll pay the extra for the mitsu model as they are built to the specs we NEED and move coolant well at all RPM's
I first suspected this because no matter how well i maintained the cooling system I've had overheating issues under light loads with the AC on only, i can boost 30psi all day in 90+ ambient temps with no overheating)
one day while inspecting things noticed i would have the one heater hose colder than the other and i would have to rev the engine to get heat, and it would fade again at idle...the pump just wasn't moving the water until it was revved
You see, some will blame the radiator, but when your just cruising and have the stock cooling system (complete with OEM fans) you should never overheat even with the AC on, i don't care how built the engine is. this is because heat is a form of energy transfer from the energy created in combustion... but when you're off boost an not making much power (or energy) the stock system should be more than ample, but if it's not doing the job under daily driving then you have an issue (duhh) but as far as big aluminum radiators and such, they are not needed unless your road racing or running the car for long periods under high power (making more energy dispersed heat than the system was designed for for prolonged times)
the thing is a perfectly good/new reman or aftermarket water pump can cause you to overheat even though nothing "seems" wrong with it and you just put it on
Here's the deal....The tolerances of impeller to housing and the impeller shape and angle of fins on some pumps are not the same as OEM therefore they start to suffer from suction loss on the side they pull the coolant into themselves on. This causes poor circulation and many other things (similar to when an oil pump gets too much clearance and goes bad)...there's only one way i know how to test this but it's a pita, and ill explain in a minute.
But first off, I wish i wasn't packed up and had a camera to get some pics to show you but i compared an OEM to "reman" pump and saw enough differences to convince me to test mine for flow other than just function and found my issue
What you need:
4 hose clamps the size of the heater lines
some radiator hose and 2 pieces of solid tubbing to extend your heat lines
2liter bottle, (clear)
some wire for hanging bottle
a good thermometer that will reach 200+*
How to test:
First this is messy!
you need to take BOTH heater core hoses off and run them outside the car with some extension tubing from autozone..then cut the top out of a 2 liter bottle big enough to put both hoses in and find a way to elevate it to the height of the engine or a tad higher (make sure that both lines stay submerged in water/antifreeze (you may even want to put some water in the jug before starting the car to avoid pulling in an air bubble)
At this point you want to plug your radiator overflow hose as well because if pressure builds that's a whole other issue
Now, with both hoses in the suspended 2 liter bottle, start the car and start warming it up... the coolant will flow from the "out" heater line into the bottle and the pump SHOULD suck it up with the other hose thus giving you an un-pressurized but flowing cooling system
Now as coolant expands of course the bottle might overfill (no worries, dump some off)
What you want to do is.
A.) look for bubbles to start forming while measuring temps of the fluid... bubbles mean it's boiling and this shouldn't happen to at around 180* or so, if it happen earlier the pump probably isn't flowing right, or there could be a head gasket leak letting hot gasses ito the system, this would be accompanied with a lot of extra bubbling in the coolant as well.
B.) make sure that the pump is sucking out the same volume of fluid from the 2 liter that it's pumping into it.(within reason, a slight difference isn't bad, but i do mean SLIGHT). if it's boiling earlier from the reading at the bottle (not the gauge ) or it it's not keeping up with sucking the fluid out as fast as it's going in, well, your pump is not working very well and needs replaced (even if it's new it's no good...fact)
Now since the overflow is plugged and we have an "open in/out" bottle we shouldn't have pressure (this is why the coolant should boil also) if your upper radiator hose is pressurized then you likely have a clogged cooling system that needs flushed and possibly a blown head gasket depending on the bubbles and temperature of the boil
If you suspect a HG just rent or buy a leak down tester and that will tell you FAST if you have a HG issue... in fact with the Rad cap off you can usually hear/see the system bubble with the car off and pressure in the blown cylinder.
this water pump flow issue is a little known, but probably more common cause then you would think when you're driving and everything is cool until you climb a slight hill, accelerate in traffic and so forth but not using any or much boost. a bad HG will push coolant under higher boosts and that's different.
I'm feeling sick today so if i think of more I'll add it on here, but now i know i have a water pump job ahead of me and I'm not buying another reman or aftermarket pump again, I'll pay the extra for the mitsu model as they are built to the specs we NEED and move coolant well at all RPM's
I first suspected this because no matter how well i maintained the cooling system I've had overheating issues under light loads with the AC on only, i can boost 30psi all day in 90+ ambient temps with no overheating)
one day while inspecting things noticed i would have the one heater hose colder than the other and i would have to rev the engine to get heat, and it would fade again at idle...the pump just wasn't moving the water until it was revved
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