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engine over heating

22K views 17 replies 7 participants last post by  Dr. Dyno 
#1 ·
Hi ,
Our rav has cooked itself , once cooled down & refilled with water it starts & runs just as good as it did before hand & slowly heads toward overheating again .
So Far I've checked for leaks & replaced the thermostat after trying with no thermostat it still overheats & blows all the water/coolant out through the over flow bottle with the thermostat fitted or not . I have revved the engine up with the radiator cap off & it pushes the water /coolant out so I'm assuming the water pump is ok .... I've come to the conclusion that either the head gasket is blown or the head is cracked & leaking compression in to a water jacket , there is no oil in the water/coolant & no sign of water in the engine oil . the rav showed no signs of running hot previous to the 1st over heat so I'm assuming the radiator is not blocked . the vehicle takes about 15 mins from cold to get to where I shut it down before it gets dangerously hot .
Any info on common overheat causes with the rav ? are they known for head gasket failure or cracking heads ? at the moment the vehicle is about 20 miles from home & I hope to sneak home in the cool of the night stopping when necessary to cool down & refill to get back home & start the diagnosis/repair process . Please let me know if you have tips/advice etc as you may be a massive help .
thanks
Austin
 
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#2 ·
Austin FWIW, I've seen water pumps with impeller vanes that have corroded down to nubs. They will push some coolant, but not enough. I've also seen water pumps where the impeller slips and only works at low rpms. So don't just assume it's good.
 
#3 ·
Do you know why the first overheating happened? It would be unlikely to all of a sudden develop a head gasket leak. What is happening with the cooling fan. You should have two fans. One is the radiator fan and one is the A/C condenser fan. If your temp is high then the radiator fan should be running. If it is not then check to see why it is not. The coolant coming out of the radiator filler would be a normal thing if the coolant temp is greater than boiling temp. With the radiator cap off, the system cannot pressurize and will boil. The development of vapor in the system will push coolant from the opening. It will also pressurize the system to greater than the radiator cap relief set point and it will push everything through the overflow bottle. If your radiator fan is working correctly and you still are experiencing overheating. I would make sure the water pump is working correctly.


There is a test that can be performed on the coolant system for combustion by products. If they exist it is coming from a combustion leak into the cooling system via a head gasket leak(normally). A combustion leak into the cooling system will drive temperature up pretty quick. The cooling system is not designed to handle that amount of heat load on the system.
 
#4 ·
Hi Everyone thanks for your advice so far , I'm not sure what caused the initial overheat , it was bad as I first noticed it when there was a puff of steam from under the hood & looked at the temp gauge it was way up close to the red ... I let it cool for 4 hours then started it it ran as per normal so refilled with water & limped to my sisters 3 miles away ,thats where I looked at it closer, I'm going to bring it home slowly tomorrow & get really stuck in & see if I can figure the problem . the fan works until I'm assuming the water/coolant turns to steam or boils then no fan running , the engine runs fine when warming up & hot ,when up to operating temp it then heats up rapidly then starts blowing steam out through the overflow bottle etc that's when I shut it off before it gets too hot .
Am Iable to see the water pump impellor through the thermo stat hole ? if I remove the thermo stat ? many thanks so far
 
#5 ·
So you only have one fan? It could be defective, failing when it gets too hot.
 
#6 ·
Removing the thermostat is not a good thing. The coolant flows too fast to cool down the engine.


I don't like the fact that the coolant spews out the filler. That is a sign of combustion gasses getting into the cooling system.


Does the radiator fan come on when the AC is on? Does it come on by itself after 10-15 minutes and turn off?
 
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#8 ·
Removing the thermostat is not a good thing. The coolant flows too fast to cool down the engine.


I don't like the fact that the coolant spews out the filler. That is a sign of combustion gasses getting into the cooling system.


Does the radiator fan come on when the AC is on? Does it come on by itself after 10-15 minutes and turn off?
not necessarily...if it overheats thats whats going to happen.
 
#7 ·
Temp sensor might be bad since the fans are connected to that somehow. Or are you sure both fans are working? check fuses/relays for the fans. You said you replaced the thermostat?

Its possible its a head gasket...but if you have the radiator cap off and no air is coming out of it, it doesnt sound like a head gasket.
 
#9 ·
With a failed or failing head gasket a constant stream of bubbles will come out of the radiator even with the engine cold or cool before any steam develops. I'd suggest checking for bubbles ASA you start the engine. You should expect to see some right after adding water due to air purging itself out but it shouldn't be continuous.

Also never ever pour cold water into a hot radiator w/o the engine running. If you shut off the engine to add water the slug of cold water will crack a cylinder wall when you restart the water pump.
 
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#10 ·
thanks for all the info so far ... just so everyone is on the same page , there are 2 fans one for a/c & one for radiator , I put a new thermostat in the car after trying without one fitted as the temp went straight up with out one fitted . I've made sure the engine has cooled down before refilling the coolant .
My main concern is the initial overheat it was really hot when that happenend & I let it cool down for 4hours before refilling...when we purchased the vehicle 2.5 years ago I could see someone has had it apart to service the valve clearance & cam belt & possibly had the head off... I have been wondering if it was not torqued down properly if they had the head off .. there are no bubbles in the water /coolant with the engine running once the system is purged of air after refilling however am wondering if once the temp increases if there is a crack in the head that opens up & allows the compression to leak into the cooling system or if the temp increase allows the head gasket to start leaking compression into a water jacket by the time the temp is at this point I can not check for bubbles in the water as it is starting to blow steam ...the cooling fan will switch on initially when it first gets the signal from the sensor as the temp rises .. then if it gets to blowing steam the fan does not operate I would assume that the sensor needs hot liquid around it to send the signal to the fan as opposed to steam & there fore may not trigger the sensor , please tell me if I'm incorrect about my theory with the sensor .
well I'm off to get the poor old rav & bring it home slowly it will be a long trip .
thanks Austin
 
#11 ·
Okay, lets review. You have a 1995 RAV4 with probably a zillion miles on it. In New Zealand temps are warming since you're in summer not winter like most of us in the northern half. It's hitting freezing in CT, USA.
Maybe we're over analyzing this. Before we wonder about the head having been off etc, could it be that the initial overheat was due to the aging radiator just not being able to keep up with the warmer weather? Check it for disintegrated or clogged fins. Maybe there's nothing wrong with the engine.

Happened to me on a very high mileage Accord years ago. It kept running warmer & warmer altho I never allowed it to overheat knowing that's the easiest way to blow a head gasket. Bought a new radiator very cheaply on eBay, installed it in 15 minutes and all was cool again.

Another point: Except with the A/C on on the very hottest of days, driving on level roads at 60 mph or so with a properly working cooling system creates enough air flow to cool the engine w/o any fans running. So you should be able to pull onto a highway starting with a cold engine and drive w/o needing the fans until you slow down again.
 
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#12 ·
Hi , thanks for the advice & have a happy new year , I spent yesterday & some of today working on the rav , before I did my journey home I put a new radiator cap on & that made a huge difference so the trip home was better than expected , now the cooling fans have stopped working , once home I was relieved the head gasket is intact in my opinion now , I flushed the radiator , checked fuses , relays , fans & replaced the thermo switch as the old one was defective according to the ohmmeter .still no fan coming on except for once at too high a temperature for my liking . the radiator is in good condition .
So in the meantime I've cut one of the wires to the thermo switch & wired a switch to the dash so I can switch the fan on manually when needed as I do a lot of towing in hilly areas & mild off roading on the beaches where I live , I guess the way I've left the wiring intact if the fan decides to start working at the right temp I will know if I'm not operating them manually .
sorry if I've led you astray with my earlier comments , I'm used to old vehicles with much larger cooling systems by todays standards & really thought the rav had cooked itself good & proper .
happy new year !
 
#13 ·
Flushing the radiator probably helped a lot. To help clean the engine and radiator cooling surfaces for better heat transfer I often add some low sudsing laundry detergent to the system, drive for a few days and flush the system again before adding coolant.

BTW, I'm sure you know that your ohmmeter test should show the thermo switch open until subjected to high enough temps.
 
#14 ·
:D many thanks for the info & help the people & this website has given me , this has saved me having to buy a workshop manual for the rav , I'd like too & cannot find a decent one over here only Haynes which in my opinion are rubbish , I've found info on this website that is far more informative like awkward hidden bolts for example .
Well the rav overheat saga carried on once a week a new leak & been fixed as the leaks came , I ended up replacing the water pump & rear housing & put a cambelt kit & seals in .. so hopefully that is it sorted ,just goes to show how running hot will cause other parts to fail.
I think you need to have a little bit of contoursionist in your blood line to do this work to the rav ... I 'm glad I did the cambelt as it had either been assembled wrong or skipped a tooth before I got in there it goes a lot better now.
I could not see the timing marks line up on the cam wheel with the mark on the bearing cap when reassembling , so removed the cam wheel again & made some marks with a pen & straight edge that are visible with the cam wheel on & also found some old fencing wire that fits the hole in the cam wheel that you line up with the mark , I ground one end of the wire to a point poked the wire through the hole in the cam wheel & could feel the notch / mark when the cam is in the right position for reassembly , hope this helps someone else who is having the same problem .
I have one question is it normal for the a new cambelt to be slightly noisier than the old one ?
thanks for all your help
 
#15 ·
My cam belt went from noisy (flappy) to dead quiet when I did it on Bluey RAV, not sure whats going on with yours if its suddenly gone noisy?

But you are not wrong about needing to be a contortionist to change it :D. its manageable, but not that easy.

Although it will not increase coolant flow due to a bad water pump, I have limped cars home by running the AC with the compressor clutch disconnected. just turn the cabin fan to Min, then turn it on, the condenser fan will help out without the added heat of compression from the compressor, just something to think about if anyone is stuck in traffic with a dead radiator fan on a hot day. I saved my BM 7 series head that way after the visco fan went limp. (Note, fan may not come on if AC system is not charged (LP cutout engaged) but you could also bridge that out in an emergency)
 
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