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1998 RAV 4 3S-FE Engine Temp Issues

21K views 44 replies 8 participants last post by  Dr. Dyno 
#1 ·
Live in Costa Rica, very hot climate
Bought RAV 4 first drive 4 hours from San Jose to my home Temp gauge showing very hot all the way to H. Let sit cool down. Temp gauge would fluctuate as I drove from center to high.

Replaced Radiator, Temp Sensor, removed Tstat, flushed cooling system completely.

After the above repairs it drives fine when driving on easy to moderate terrain even for long distances.

The issue is now is anytime I am driving a mountain pass for a long distance the Temp gauge begins to move up, gets to about 3/4 high and then stays for a bit then drops back down. If I am going slow it does this more often than if moving faster (probably the engine is getting more wind through the radiator). I have spoken to my mechanic and we are not sure what could be causing this. The engine is not overheating, and everything checks out ok.

let me know if you need more info.

Any recommendations appreciated.
 
#2 ·
Have you checked that the electric fan is coming on, you didn't mention it in your post?

If I leave my Rav running on tickover when hot, the fan will trip in about every 5 - 10 mins or so and run for about 30 seconds before switching off. My temperature gauge shows a little over halfway when the fan trips in.

I can imagine on steep climbs, in a hot climate, when going slowly, the electric fan would trip in and out as needed to keep the temps correct.
 
#6 ·
My 97 does the same thing. It used to run a lot hotter until I had the radiator flushed. Now it runs cooler unless climbing. The fan will come on when the temps get around the halfway mark, but no other problems. My RAV has 172tmls.
 
#7 ·
the thermostat restricts the flow thru the radiator so that it stays longer and cool better, if you re,move it it not only takesd longer to warm up it will never cool properly because the water needs to stay in the radiator to cool, if it just runs thru it cannot she dthe heat it needs to
 
#9 ·
the thermostat restricts the flow thru the radiator so that it stays longer and cool better, if you remove it it not only takes longer to warm up it will never cool properly because the water needs to stay in the radiator to cool, if it just runs thru it cannot shed the heat it needs to
Actually the purpose of the thermostat is to hold the coolant in the engine until it reaches operating temperature so I agree that w/o one the engine will take longer to warm up. In fact if the system is working properly it will never warm up. But higher flow thru the radiator will end up producing more cooling not less.

My question to the OP is is the system completely filled and does running the heater, yes I said the heater, change anything?
 
#10 ·
The cooling system is completely full, according to what I can tell by the radiator and the overflow, and per my mechanic. I have not tried turning the Heater, although no heat will generate because the TSTAT is gone. I will try that.... what are your thoughts if this makes a difference in the temp gauge?
 
#15 ·
... I have not tried turning the Heater, although no heat will generate because the TSTAT is gone. I will try that.... what are your thoughts if this makes a difference in the temp gauge?
Whether the thermostat is installed or not the water temperature in the heater will be the same as in the engine as long as the water pump is functioning properly. So the amount of heat should mimic the gauge. If there's no heat then either the system is low on water or your temperature gauge is wrong if it reads normal or hot.
 
#11 ·
a heat exchanger will remove more heat the longer the heated water stays in it, a diaphragm type thermostat controls the flow of the water even when it is open, it is a restrictive device, thats how it works if the liquid runs thru it does not remove heatr as efficiently, if you want more flow, leave it out, but it will not work right ever
 
#16 ·
Must have been a really old car for the pump fins to disintegrate that much. Most modern pumps use plastic impellers anyway.
 
#13 ·
When you say you removed the T'stat, did you just to it to flush then put it back (assuming its still good) or is it left out altogether?

Just as Onetimeuser says, Running no T'stat at low speeds and in stop-start seems to work okay until the head cracks due to thermal shock (really old all iron engines did not seem to mind, but running a new one with no thermostat can kill it)

If the thermostat is missing, the coolant is passing through the radiator constantly and cannot dissipate enough heat due to its excessive flow velocity, the thermostat restricts the flow, and shuts it off when the engine it getting too cold.

Even in a colder climate like where I am, if I took the T'stat out and hit the highway in ANY of my cars, I would experience the same thing, over-cooling at low speeds in traffic, overheat on the highway or pulling hard for long periods of time (IE going through mountains)

replace the thermostat with a good new one and she will be good as gold.
 
#17 ·
...
Just as Onetimeuser says, Running no T'stat at low speeds and in stop-start seems to work okay until the head cracks due to thermal shock (really old all iron engines did not seem to mind, but running a new one with no thermostat can kill it)

If the thermostat is missing, the coolant is passing through the radiator constantly and cannot dissipate enough heat due to its excessive flow velocity, the thermostat restricts the flow, and shuts it off when the engine it getting too cold.

Even in a colder climate like where I am, if I took the T'stat out and hit the highway in ANY of my cars, I would experience the same thing, over-cooling at low speeds in traffic, overheat on the highway or pulling hard for long periods of time (IE going through mountains)
Where are you guys getting thus stuff??
If thermal shock was going to happen it certainly wouldn't without a thermostat where the continuous flow would maintain the most constant or gradually changing temperature.
If shock was a problem it would be most severe in a cold climate with a thermostat blocking flow as the engine gets heated up. Then its opening allows cold, possibly very cold, radiator coolant into the engine. Talk about thermal shock! Fortunately thermostats are very slow opening devices to allow the cold coolant to mix in gradually.

If you guys still believe that a higher flow rate means less cooling in a radiator and a lower rate means more, but overlook that the opposite is happening in the engine, that is a lower flow rate generates more higher temps, such that higher flow thru the whole system minimizes engine temperatures, well then, I give up. :shrug:
 
#14 ·
Another thing to note is, the ECU in most cars will not change over to a "hot engine" fuel delivery map, so when its running cool, you are running on cold start injection, and wasting fuel.
 
#18 ·
So I am a bit confused.... Should I replace the TSTAT or leave it out? I tend to side with Dr. Dyno on the fundamentals of cooling in relation to a TSTAT. But should I have it put back in. My Mechanic strongly believes that it does not need to be there, because of the hot climate area the engine gets to operating temp quickly, so with out it you have constant cooling of the engine resulting in a better form of cooling. That seems to be the case with normal to moderate driving but not when working up hills long term.
 
#19 ·
My main concern is that the cooling system should be able to keep the engine temperature below hot even up hills in a hot climate. And all removing the thermostat should do is make it run cooler overall thus leaving more temperature margin before hitting the hills. But as Aussie50 says, unless it warms up enough the ECU will make it run richer than normal.
When you say, "the engine gets to operating temp quickly" what we need to know is what is that temperature. Is the gauge reading correctly? That's why I suggested checking the heater output. Starting from a cooled off engine it should be cool. When the gauge reads 1/2 it should be warm. At 3/4 it should be hot. If all that checks out the gauge is reading correctly and I'd reinstall the thermostat unless fuel economy isn't a concern. I'd use a 180F thermostat. Again, assuming the gauge is right, the temp should read in the normal range and stay there until the hills where it may go to 3/4. I wouldn't be concerned unless it kept climbing above 3/4.
 
#20 ·
I cannot vouch for people splitting heads or blocks by removing a thermostat (couple of mechanics have told me that) but I have seen an overheat occur due to the owner taking the thermostat out, it does happen, and I advise the owner to replace his one and give it a try. if the problem does not go away, then hell, I am wrong.

There could be something else wrong with the cooling system (bad water pump or blockages?) but no mechanic in their right mind should tell you to remove a thermostat in a hot climate, then go hill climbing or hit the motorway at high speed, the engine is producing way too much heat for the radiator to dissipate with such high flow speeds through the core.
 
#22 ·
I cannot vouch for people splitting heads or blocks by removing a thermostat (couple of mechanics have told me that) but I have seen an overheat occur due to the owner taking the thermostat out, it does happen ... There could be something else wrong with the cooling system (bad water pump or blockages?)
If an engine overheats or heads or blocks crack because there's no thermostat, then I only agree that something else is wrong and that's the original cause. I've actually seen that kind of damage on a Tercel (which has it's engine mounted fore and aft so that the front cylinder is next to the radiator.) The car had overheated for some reason and ran low on coolant. With the engine off but still hot someone poured cold water into the radiator. And whether the thermostat was open or removed the thermal shock cracked the top front of the front cylinder wall ruining the block. The Cardinal Rule is you never add cold water to a hot engine. In an absolute emergency you do it only slowly and ONLY with the engine running even if steam is coming out everywhere.

... but no mechanic in their right mind should tell you to remove a thermostat in a hot climate, then go hill climbing or hit the motorway at high speed, the engine is producing way too much heat for the radiator to dissipate with such high flow speeds through the core.
Sorry, not true. Not how the systems works as a whole. If you want to insist that a high flow rate thru the radiator inhibits cooling then you also have to say the water is flowing thru the engine too fast for the engine to heat it. Do you really want to say that?
 
#23 ·
I am getting the Thermostat reinstalled today and will drive for a few day to see how that does. I am also going to try the heater core test as Dr. Dyno suggested.

One thing I will also mention is the performance overall after replacing the spark plugs and cables and Fuel filter is still not right in my opinion. Sometimes when I first start the car in the morning (not always) the engine will chug for a sec then start. The idle is at about 1000 for a while even after driving, before it gets to around 700. But the performance seems to be most noticeable when going up a hill. If I press the gas at a steady level it feels like it is bogged down, and struggles to climb. If I stomp on the gas it will jump in to a low gear and then really seem to pull like it should, but the car RPM's go really high 4500 so I let off the gas a few sec after the automatic transmission shifts down .

Any thoughts on that and is there any more info I could get you?

thanks
 
#24 ·
A new thermostat will help if all else is fine, you could have a failed water pump causing a lack of flow, but either way, you will need a new thermostat regardless of what gets replaced.

Oh, and make sure the old thermostat does not go back in just in case it was sticking shut in the first place, seen it before and its an engine killer, buy a new one.

and regardless of what Dr.Dyno says, the cooling system is a well proportioned system that Toyota spent a lot of time developing and testing, taking a crucial part out of it will make it rather unhappy.
 
#26 ·
I will also mention that when the old radiator was removed there was a bunch of sludge at the bottom looked like stop gap according to my mechanic. He is concerned that if is a head gasket when we first started with this issue we ran a test using combustion leak detector through the radiator which checks for gases. This came out ok. He also talked about the water pump and possibly being an issue as you describe above. The Heads is an enormous job and not cheap, the water pump is better.

He is going to do some troubleshooting today and retest using the leak detector. But is there anyway to test to know if the pump is bad?? My Mechanic says there is not a way to test it, except for pull it apart and inspect.

thanks much
 
#28 ·
But is there anyway to test to know if the pump is bad?? My Mechanic says there is not a way to test it, except for pull it apart and inspect.
A couple of ways. Depending on how your radiator is set up (where the cap is with respect to the top hose) you can often actually watch the water flow across the top of the fins with the cap removed.

Another way to check for good flow is with the thermostat removed and the engine idling (to please our down-under friend altho the same would be true at any speed) an infrared thermometer should show the radiator and block temps within a few degrees of each other and it should stay that way as the engine warms up.

The fact you found gunk in the radiator is an indication the block and heater core should be flushed. Last winter I fixed a friends no-heat issue on his F-150 by disconnecting the heater core and reverse flushing it. You should have seen the goop that came out! Of course that was after he froze the winter before. :surprise
 
#27 ·
The Mechanic put the thermostat in today and after driving around it gets a little above half way, on the temp gauge. Before it was a little below half way without the TSTAT.

Current theory is its possible that some water drops are hitting the pistons in the morning at first startup which is causing the ruff start up in the morning, then once they are burned off it seems to run fine, except for the heat issues when driving up hills..... and now with the TSTAT installed possibly easy to moderate driving.... i will see over the next day.

If there is a water leak in the engine what does this involve and require for a repair, again the combustion leak test was ok no gases entering the radiator. His diagnosis says it is not the water pump??

thanks
 
#30 ·
It sounds like the car has been ran without a proper coolant mix for a while and all kinds of things are plugged up, not fun trying to clean that out without using harsh chemicals (I would not advise it)

I think he needs to borescope the cylinders before going for a head gasket change, look for an unusually clean cylinder (steam cleaned valves and hard deposits on the spark plug) it will be obvious if one is getting coolant in it.

if the cooling system pressurizes very quickly and the coolant goes yellow and stinky (like a burnt glycol/exhaust smell) it could be getting small amounts of exhaust gas in it, but if he is confident its not, well, my guess is the WP, especially since old steel impellers rust away, at least if its been changed for a stainless one it may be fine, as dalbo says, you may be able to see it through the thermostat housing with a borescope.
 
#31 ·
I think he needs to borescope the cylinders before going for a head gasket change, look for an unusually clean cylinder (steam cleaned valves and hard deposits on the spark plug) it will be obvious if one is getting coolant in it.

if the cooling system pressurizes very quickly and the coolant goes yellow and stinky (like a burnt glycol/exhaust smell) it could be getting small amounts of exhaust gas in it, but if he is confident its not,
The head gasket starting to fail was my initial thought on the first post. Would allow either aeration or oil contamination of the coolant both of which would reduce heat transfer. Both would lead to overheating especially under load and explain the initial rough running. But both are easy to detect. There would either be a constant stream of bubbles with the radiator cap off or oil floating on the water or discolored coolant and oil. He'd also have either steam or smoke out the exhaust which he doesn't mention. And as you mentioned one of the spark plugs would be markedly different looking than the others.
....well, my guess is the WP, especially since old steel impellers rust away, at least if its been changed for a stainless one it may be fine, ....
I agree as bad impellers (I've actually seen broken off plastic ones) would cause low flow leading to overheating under load. But you're saying that removing the thermostat also causes overheating due to too high a flow? Having trouble making that make sense.
 
#32 ·
The issue with removing the thermostat is something I learned when being taught about heat exchangers, if the water flows through a heat exchanger too fast it becomes inefficient, the water does not get enough of a chance to absorb or loose heat, depending what part of the system its going through.
then when a professional mechanic mentioned removing a thermostat can cook an engine on the highway I found a common example of where it happens.

I am not saying its going to happen to every car, every time, but its something to consider.

Toyota put a pretty big cooling system on the RAV, so with a new radiator and t'stat it should run perfectly, however in the case of the OP's RAV, something else must be wrong if it continues to do it.
 
#34 ·
No need to take the piss...
 
#35 ·
The TSTAT is now re-installed and it gets to temp much faster. So far after about 15 min of driving the temp gauge will get up to about just below 3/4 finally the fan kicks on and it drops the gauge down to about half. It then slowly goes back up and the cycle starts again. I am planning on taking it for a little longer drive tomorrow, prior to putting the TSTAT back in as stated before I could drive for long distances easy to moderate terrain without the temp gauge getting above half. Now that the TSTAT is back in it seems to be rising quicker, and in a shorter span of time.

My question is should I try having the water pump and belt replaced first, or should I just have the head gasket replaced and then do the pump and belt at the same time. The Head gasket is a much bigger job and costs much more. I still don't have an absolute surety it is the head gasket. Also would I be able to be driving it around for the last 6 months without it blowing or overheating if it was the head gasket?

thanks much
 
#36 ·
Sounds like water pump, I would get borescope inspections done first before doing the head, it will be obvious if coolant is getting into the cylinders, and if exhaust is getting into the cooling system.
 
#37 ·
... it will be obvious if coolant is getting into the cylinders, and if exhaust is getting into the cooling system.
Agreed, and I actually wonder if everything but the rough startup isn't normal.

The thermostat is doing what it's designed for - keeping the flow to a minimum so the engine warms up quickly until the thermostat's temperature is reached. Then opening to hold that temp. Apparently there's some overshoot for some unknown reason. Possibly the thermostat is sticking while opening and closing. I've tested them in a pan of water on a stove with a candy thermometer. You can watch both the movement and the temp it happens at.
BTW, is the thermostat a new one or the old one?
 
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