Overheating prob.

[thaharlequin]

O.k.. symptoms are overheating, coolant overflows, etc. It'll overheat sporadically, the gauge needle will jump up and back off, then jump higher, etc... The top coolant pipe going into the heater core is hottest, the top pipe going into the radiator the next hottest, then the bottom radiator and bottom heater core pipe. Everything's fine as long as I rev the engine periodically or keep the speed at ~4k rpm in 2nd. I'm guessing the water pump's slipping, but I wanted to double check, so if anyone had any other ideas like thermostat, etc...

[Stillrunning]

Engine, year?

Do the cooling fans come on?

[hooRAH]

If you increase cooling by increasing engine RPM (assuming you're traveling at the same speed), its a textbook case of the waterpump not moving enough water. You'll need to replace the timing belt and the water pump at the same time.

It has nothing to do with the thermostat or cooling fans.

[thaharlequin]

O.k. Thanks for the info!

[Stillrunning]

Originally Posted by hooRAH

...its a textbook case of the waterpump not moving enough water. You'll need to replace the timing belt and the water pump at the same time.

To assume waterpump not moving enough water you have to assume 1. badly worn impeller or 2. rotation of water pump not fast enough

If the cooling system has had at least some care I doubt worn impeller unless no antifreeze was used and it has corroded. thaharlequin has not complained about a leaking waterpump, so I assume shaft seal is ok. How would the water pump not spin fast enough? It is direct drive off the timing belt and unless the pump shaft is sheared or the T-belt is slipping, which would present other more serious problems, there is no way for the water pump to spin slower.

thaharlequin, get back to us on the condition of the water pump after you have it torn down.

[hooRAH]

I was going towards worn impeller.

I figured it wasnt having not enough antifreeze, as he mentioned it overflowed (which says its boiling, not overfull, but it should have enough in there to overflow).

The timing belt can't slip but one or two teeth (and you'd know it), but waterpumps with plastic impellers are not unknown to losing a blade or two when they get old.

[Stillrunning]

It has a plastic impeller???

[Eye8Pussies]

yup....they're plastic.

never heard of one losing blades, but it's possible I suppose....

[Stillrunning]

I've never seen a plastic impeller. My Camry certainly doesn't have one. thaharlequin didn't post his year or engine, why would you assume he has a plastic impeller?

[thaharlequin]

92 3VZ. All I know is the coolant won't circulate unless the engine is spinning over at a fairly good clip. If I pull over and stop, or even cruise like normal in 4th, the air from the heater core isn't too hot but the gauge will spike when the car's running. If I rev it it drops momentarily it'll drop, and driving at ~55mph in second seems to keep temps normal, along with realy hot air like I'd expect. It's so pronounced I can go up a ~5% grade at 4k rpm/55mph w/ stable temps, but if I coast down a grade in N at 55mph, the temp will climb quickly.

[Stillrunning]

It sounds like a flow problem, but flow is also determined by restrictions to flow not just the water pump. Before I would go dismantling the engine I would look to simpler solutions. If there is a restriction then reving the engine could overcome the restriction. Have you maintained your cooling system? When was your last timing belt change with water pump? Right now I'd replace the thermostat, cheap and easy try. Are you getting boiling water coming out of the ovewrflow? If so I'd replace the rad cap.

[thaharlequin]

What would boiling water coming out of the overflow have to do w/ the radiator cap? I was also thinking the thermostat may kinda sorta be going, so that enough flow from the water pump can help push it open, so I suppose I should boil that to check it before disassembling everything. Otoh, the timing belt does need to be change, coolant flushed, etc...

[Stillrunning]

The rad cap maintains pressure in the system, higher pressures mean higher boiling temperatures. if the fluid boils it will blow out the rad cap. You don't want the fluid to boil. I'm not saying that's your problem, but it should not overflow the overfill reservoir, just expand slightly into it. You will probably notice this more when the car is hot and shut off. The engine increases in temp before starting to cool down after shut down.

[thaharlequin]

Which way does the coolant flow through the head and into the heater core? What I found really odd was that the hottest was the line out of the head to the heater core where the thermostat is. The heater core would only get "new" hot water when the engine was revving. If the thermostat wasn't opening, wouldn't this line be cooler, since there would be no flow out of the head?

[Stillrunning]

That would be normal. The flow is from the lower rad hose (cooled fluid), through the thermostat into the engine and head, out the other end of the head where your heater hoses are and the outlet to the upper rad hose. You want heated fluid for the heater core, so that fluid will be the hottest as will the upper rad hose. You might try squeezing the lower rad hose closed before the thermostat when the engine is hot and running, watch for spinning belts and hot places, and holding the hose closed for a few seconds. When you release it you should feel a rush of water if the thermostat is fully open. If not there is a restriction. The only point of restriction in the system is the thermostat unless your rad is plugged with debris. I guess it could be a bad pump impeller, but I've never seen one, and with all the work needed to change the water pump I would not look there first.