DIY Overheating Diagnosis

[Mellow77]

Sorry to keep ya'll waiting; been slammed trying to play catch-up after my trip.

It does sound like your truck overheats only in extreme situations, when its under load up a hill hot out with the AC on, other than getting the stock fan to work properly ie install that new fan clutch, i am not so sure there is an actual problem with your truck. 100*F outside, witht he AC on will certainly push a motor, now going uphill for an extended period of time will definetley push the motor hotter. I would fix the and really just expect that if you push the motor to its limits like that, that it will overheat, i mean the air cooling that coolant is at lowest whatever the outside temp is, and then you have the extra heat from the AC in the engine bay so that engine bay is probably close to 150-200*F, i dont know how you can expect the coolant to be cool when the air its using to cool it is stagnent engine bay air mixed with a little outside at 100*F. I'm not sure you will find many 3rd gens that wouldnt overheat in that situation.

Although this is logical, and acknowledged as a possibility by the Toyo Specialist, I really have a hard time accepting it. If I was pulling a trailer, boat or had some big cargo deal on top of the truck then I might be able to accept this as a reality. 3 dudes and our backpack hunting gear hardly constitutes a heavy load even when climbing mountain passes.

Has there been any test for exhaust gases in the coolant? Does the system appear over pressurized? (Puffy hoses, whistling rad cap, foam?)

Also get an UltraGauge so you can get some actual numbers. The dash gauge is useless. It doesn't really start to move from the middle for me till AFTER 230F which is already well into way too hot to be working right.

No puffy hoses, whistling or foam. I watched my torque app like a hawk all the way to CO and back to get some insight into what's actually going on between the coolant temps, tranny temps and engine timing.

You replaced the radiator but what about the cap?

Brand new cap was used with the new radiator.

Good point ! Also...make sure you set the climate control to hot and make sure you fill up the heater core.

Did that several times during the burping process.

electric fan. ie no fan clutch.

I don't think it is your fan because i would bet that the truck moving at 50-60 mph is gonna move much more air through the radiator than the fan will with the truck stationary. If the original red coolant wasn't COMPLETELY flushed out, that could be the cause since mixing the green with red can cause gelling. I know you say you flushed and refilled again but what does your coolant look like? If it kinda brown, i would

Great point and one I was determined to eliminate as a possible cause of the problems. Coolant is back to Toyo Red after another full flush by the Toyo Specialist.

Bad thermostat, but stuck open and or too low of a temperature
Rating. Get a 190 degree one.

Reason ..... When stuck open the
Coolant does not stay in the radiator long enough to be cooled.

Good thought, and I suppose a possibility with a bad*ss water pump but running w/o a thermostat actually just delays your warmup time in cold weather so defrost and heating functions may suffer a little. A brand new Toyo OE thermostat was put back in the truck.

I had a similar issue with my '86... with my head under the hood, I saw the hose that feeds the water pump had collapsed. I could drive at highway speeds fine, but stop and go or working it up a grade was a pain for the heat reasons. New hose and things went back to normal.

Although, I am leaning towards gelled fluids from the one who blew out the wiring...

All hoses are in good shape; no collapses, leaks..etc.

shut the AC off in the blistering heat in stop and go traffic.

Not a viable solution...did you miss the part about living in TX???

I will be the first to say it.

I am not a toyota specialist but I am willing to bet all the money in my pocket that it is a bad head gasket or a cracked head.

Sing, instead of your money I'd rather put your skills to work under the hood of my rig. She needs some more power and after drooling along with your v8 conversion you've got more to offer than cash! In this instance you'd be wrong even though I was terrified at one point that's the only thing it could've been.

You're second to suspect the heads/gasket..."Has there been any test for exhaust gases in the coolant?"

Toyo Specialist confirmed absolutely no traces on anything else other than coolant, which was a HUGE relief to me.

To go another step further I performed a compression test to see if there was anything else I could learn. Results were pleasantly surprising!

1 - 210psi / 2 - 210psi
3 - 205psi / 4 - 200psi
5 - 210psi / 6 - 210psi

OK Mellow77, what says the Toyota Specialist?

I wish I had a better answer but after checking everything out the specialist concluded it must be the electric fan setup despite it's greater than stock CFM capabilities. He was not able to duplicate the problem but thought the missing shroud definitely is making a difference and also said the Satoshi grill mod could be slightly constricting the airflow to the radiator. :dammit:

I don't want to give up on the electric fan setup so I plan on integrating it into the factory shroud and taking some CFM measurements in various configurations to see if I can get some actual data to support what is going on. I will report back when I get some data to go along with the different setups.

So I guess those who voted option #4 "Electric Fan Setup is not cooling properly" technically win based on the Toyo Specialist's findings. I personally think those who voted option #7 "???? - Ya got me stumped!" should be the winners based on the lack of evidence and an informed guess by the specialist based on a process of elimination.

Thanks for all those who participated!

 

[Singtoe]

Doesn't make since. The problem you have is at speed. The fan issue would be a problem at idle because of no air flow.

But wait, New theory.


This may be dumb question but are you fans spinning in the right direction? Are the pulling air or pushing air.

I can imagine at speed, if the fan was pushing air into the oncoming air, it could cause an air damn preventing air from flowing.

But at idle, it is pushing air through cooling it down.

 

[nevada]

Fact is that a stuck open thermostat cannot physically result in overheating without other issues with the cooling system. Seriously, the worst thing a stuck open thermostat will do is keep your engine temp lower than optimal – never ever higher. It’s physically impossible.

that is simply not true.
you are 100% wrong.
now, im not saying that is the case with this 4runner, or that its even possible with THAT vehicle. but it absolutey IS possible, and happens.

if the coolant is moving too quickly through the rad, it wont have time to cool down enough. so it will reenter the engine hotter. this is usually only an issue on something with small capacity. motorcycles, 4wheelers or the like. maybe even a small 3-4cyl car. but, to say it cant/doesnt happen is both ignorant, and ridiculous.

again i will say, i doubt this is an issue with the 4runner. its got a pretty big rad, even fully flowing, there should be enough surface area, and cooling capacity to reduce the heat enough.

 

[agloukhoff]

that is simply not true.
you are 100% wrong.
now, im not saying that is the case with this 4runner, or that its even possible with THAT vehicle. but it absolutey IS possible, and happens.

if the coolant is moving too quickly through the rad, it wont have time to cool down enough. so it will reenter the engine hotter. this is usually only an issue on something with small capacity. motorcycles, 4wheelers or the like. maybe even a small 3-4cyl car. but, to say it cant/doesnt happen is both ignorant, and ridiculous.

again i will say, i doubt this is an issue with the 4runner. its got a pretty big rad, even fully flowing, there should be enough surface area, and cooling capacity to reduce the heat enough.

No. That's not how cooling systems work. I worked on watercooling for computers for years, personal stuff and IBM mainframes, bikes, cars etc. High flowrate will NEVER result in reduced cooling. It's just not physically possible. (Ok, it IS if you have lots of air in the system which will cause bubbling and foaming which is really an issue with the AIR rather than flow rate)

Fast moving water will only result in very little tempriture difference between the in and out on the radiator, but it will still be cooling whatever components FAR better than a slow moving system that allows for massive tempriture difference between radiator input and output flow temps.

For example, a LOW flow system temps may look like this:

Rad In: 210
Rad Out: 170
Engine Internal: 230

High flow would look like this:

Rad In: 190
Rad Out: 180
Engine Internal: 220

VERY high flow would look like:

Rad In: 188
Rad Out: 184
Engine Internal: 200

This gives the impression that the radiator isn't working, in reality the heat dissipation is WAY higher as thus so is the cooling capacity as more heat is being moved OUT of the engine which is what you are trying to do. You are trying to cool the ENGINE not the coolant. The coolant is just the means of moving the heat out of the engine to the radiator and into air.

The whole "needs to stay in radiator to cool" is a misconception and anyone with any cooling experience will tell you so. This is why you get "High Flow" radiators...

I'm done ranting. So you can either take my informed opinion based on experience or disregard it. Your call.

 

[Mellow77]

Doesn't make since. The problem you have is at speed. The fan issue would be a problem at idle because of no air flow.

But wait, New theory.


This may be dumb question but are you fans spinning in the right direction? Are the pulling air or pushing air.

I can imagine at speed, if the fan was pushing air into the oncoming air, it could cause an air damn preventing air from flowing.

But at idle, it is pushing air through cooling it down.

BINGO, that's where my head has been! The only thing that would explain that is the grill mod blocking air into the rad but I just don't see how that's possible thus wanting to measure the CFMs somehow.

Not a dumb question; at this point I'm considering everything. The fan was bought and installed as a "puller". With the hood open and the fan on I can stand by the drivers door and feel a stiff breeze from the fan. I'm struggling to see how it's an airflow issue.

 

[agloukhoff]

Do you currently have a fan shroud at all? (You really need one)
Is it one of those fan and shroud in one setups that you tie to the radiator? (Does it leave gaps?)
How much space is there between the fan and the radiator? (You want as little as possible)

I am having a tough time accepting the radiator fan as the issue. I've driven track cars with electric manual fans that you need to turn on with a switch, and those things stayed off except when pulling into the pits. Hell that's the setup that was going on to my E30...right up until I sunk my E30 money into a JDM engine...

Anyway, you should be able to feel air getting sucked into the radiator from the front with the fan on.

Keep in mind that electric fans that may have 4000+ CFM ratings but have far less power behind the blades than the belt driven one. This means that once you strap it to a radiator and it has to actually pull the air through, the actual quantity air moved THROUGH the radiator is far less than the 4000CFM especially if you do not have a shoud. The fan will suck in air through the easiest means, meaning if it's easier to suck in air from around the shroud or the sides of the fan rather than through the radiator, that's what it will do. You'll still feel air blowing behind the fan but it won't be doing much good to the radiator.

Easiest way I can think of testing your fan would be to block of parts of your radiator (slide cardbord in between your rad and ac) this will let you get hot on idle, manually turn the fan off and on to see if it's able to bring the tempriture down at all or if it's pulling around the rad.

 

[MadCityRich]

Assuming good air flow, good coolant, good radiator, good radiator cap, good thermostat, and properly burped system, my thinking is the water pump.

Of course you could take advantage of the situation and start using the heat for some tasty cooking.

MadCityRich
2002 4Runner

 

[cj80cruiser]

I remember another member on here had issues with over heating after installing electric fans. He ended up removing it.

 

[NOT ME OR SOMEBODY]

No. That's not how cooling systems work. I worked on watercooling for computers for years, personal stuff and IBM mainframes, bikes, cars etc. High flowrate will NEVER result in reduced cooling. It's just not physically possible. (Ok, it IS if you have lots of air in the system which will cause bubbling and foaming which is really an issue with the AIR rather than flow rate)

Fast moving water will only result in very little tempriture difference between the in and out on the radiator, but it will still be cooling whatever components FAR better than a slow moving system that allows for massive tempriture difference between radiator input and output flow temps.

For example, a LOW flow system temps may look like this:

Rad In: 210
Rad Out: 170
Engine Internal: 230

High flow would look like this:

Rad In: 190
Rad Out: 180
Engine Internal: 220

VERY high flow would look like:

Rad In: 188
Rad Out: 184
Engine Internal: 200

This gives the impression that the radiator isn't working, in reality the heat dissipation is WAY higher as thus so is the cooling capacity as more heat is being moved OUT of the engine which is what you are trying to do. You are trying to cool the ENGINE not the coolant. The coolant is just the means of moving the heat out of the engine to the radiator and into air.

The whole "needs to stay in radiator to cool" is a misconception and anyone with any cooling experience will tell you so. This is why you get "High Flow" radiators...

I'm done ranting. So you can either take my informed opinion based on experience or disregard it. Your call.

I know I said I was not going to add any more to this, but your hypothectical numbers imply that you agree with me, and with higher flow there is lower delta T across the radiator.

So, the higher the flow the less cooling, EH? hmmmm... interesting.

I have had a car I bought start over heating, and it was because it had NO thermostat. The previous owner took it out thinking it would run cooler. ( I called them and while asking them if it had ever overheated on them they mentioned that they had removed the thermostat). This is real life practical experience that I have had with an automobile.

It did OK the first few months I had it, until the summer temperatures got into the 90s to 100s, then it would get too hot.

When we put one it it was OK. In the 90 + degree weather.

To the OP.
This whole was just Cheap trick I say.

If you mentioned no fan shroud in the beginning it would be easy to say that was this problem. It doesn't take a specialist to see the fan shroud, an integral part of the cooling system is missing.

 

[Mellow77]

Do you currently have a fan shroud at all? (You really need one)
Is it one of those fan and shroud in one setups that you tie to the radiator? (Does it leave gaps?)
How much space is there between the fan and the radiator? (You want as little as possible)

I am having a tough time accepting the radiator fan as the issue. I've driven track cars with electric manual fans that you need to turn on with a switch, and those things stayed off except when pulling into the pits. Hell that's the setup that was going on to my E30...right up until I sunk my E30 money into a JDM engine...

Anyway, you should be able to feel air getting sucked into the radiator from the front with the fan on.

Keep in mind that electric fans that may have 4000+ CFM ratings but have far less power behind the blades than the belt driven one. This means that once you strap it to a radiator and it has to actually pull the air through, the actual quantity air moved THROUGH the radiator is far less than the 4000CFM especially if you do not have a shoud. The fan will suck in air through the easiest means, meaning if it's easier to suck in air from around the shroud or the sides of the fan rather than through the radiator, that's what it will do. You'll still feel air blowing behind the fan but it won't be doing much good to the radiator.

Easiest way I can think of testing your fan would be to block of parts of your radiator (slide cardbord in between your rad and ac) this will let you get hot on idle, manually turn the fan off and on to see if it's able to bring the tempriture down at all or if it's pulling around the rad.

I agree with your logic and that's why I really want to test the CFM's coming out of the back of the radiator. The problem is at highway speeds pulling up a grade and even with the fan off enough air should still be forced through the rad to keep it cool.

Assuming good air flow, good coolant, good radiator, good radiator cap, good thermostat, and properly burped system, my thinking is the water pump.

Of course you could take advantage of the situation and start using the heat for some tasty cooking.

MadCityRich
2002 4Runner

I initially considered this to be the problem but the Toyo Specialist confirmed the water pump is functioning correctly.

I remember another member on here had issues with over heating after installing electric fans. He ended up removing it.

I am a little to stubborn to go that route just yet... :ybrick:

To the OP.
This whole was just Cheap trick I say.

If you mentioned no fan shroud in the beginning it would be easy to say that was this problem. It doesn't take a specialist to see the fan shroud, an integral part of the cooling system is missing.

New Parts: KoyoRad, DexCool fluid, 170 degree thermostat, temp probe / fan relay / temp adjustable harness and SPAL electric fan in place of the factory fan and shroud. I also installed a Satoshi modified grill I had been working on at the same time.

L2READ PEWN & thanks for cluttering up my thread with a pissing contest

 

[NOT ME OR SOMEBODY]

New Parts: KoyoRad, DexCool fluid, 170 degree thermostat, temp probe / fan relay / temp adjustable harness and SPAL electric fan in place of the factory fan and shroud. I also installed a Satoshi modified grill I had been working on at the same time.

I apologize I missed that.

You are right.

And too bad about the pissing match, it just irritates the hell out of me when some arrogant ass jumps on someones ideas and slams them as if they have no value at all.

And the comment he directed at his kid had me VERY PISSED.

Again I apologize to you.

 

[gmv4k]

I hate to revive an old posts, but I am having the same problem.

New radiator, flushed, new Toyota coolant / distilled water, new water pump / timing belt, new clutch fan, new thermostat.....

My truck gets hot (208 degree F) going uphills, even when it's really cold outside (20 degree F) and going 40+mph. It's fine all other times, well it ranges from 195-203 degree F. I'm thinking about checking the jiggle valve on the thermostat.

Mellow77 did you ever resolve this problem? If I didn't have an ultraguage I would never know.

I've searched and this seems to be the best thread on overheating at speed I've found.

 

[Mellow77]

I hate to revive an old posts, but I am having the same problem.

New radiator, flushed, new Toyota coolant / distilled water, new water pump / timing belt, new clutch fan, new thermostat.....

My truck gets hot (208 degree F) going uphills, even when it's really cold outside (20 degree F) and going 40+mph. It's fine all other times, well it ranges from 195-203 degree F. I'm thinking about checking the jiggle valve on the thermostat.

Mellow77 did you ever resolve this problem? If I didn't have an ultraguage I would never know.

I've searched and this seems to be the best thread on overheating at speed I've found.

I had to go back to the OEM radiator fan & shroud setup. Once I did the problems went away.

I'm convinced it was an airflow problem even though I don't see any reason the electrical fan setup I had wouldn't work. I think these trucks are very dependent on the airflow provided by the factory shroud.

 

[gmv4k]

Thanks for the reply.... I just re-read your complete thread and found the answer in an earlier post, sorry about that. I guess I'll keep searching. I think I have the original shroud in there. I'll have to double check.

 

[DocW8494]

Shroud if not on already, my eyes get screwy when reading a lot
Cracked Thermostat housing - #1 culprit - that's where my $$ is!
Water pump, but I'm assuming that has been changed within the last 100K miles.
If not that - I really want to know what it is.

 

[Singtoe]

I had to go back to the OEM radiator fan & shroud setup. Once I did the problems went away.

I'm convinced it was an airflow problem even though I don't see any reason the electrical fan setup I had wouldn't work. I think these trucks are very dependent on the airflow provided by the factory shroud.

I think that electric fans were hooked up backwards.

When at idle, they blow enough air to cool the radiator but when the air coming in from driving, the electric fans cause an air dam and the radiator does not cool.

True story. My electric fans for my 4runner stopped working ( blew a fuse) and I noticed at traffic lights, the temperature would get in the hot zone. But as soon as I got onto the highway, the air would flow across the radiator and the temperature would come down the the normal range.

 

[BrianSD_42]

Bringing this thread back to ask a decent question.

Why is it that the hot engine warning (above the middle on gauge or CEL I assume) doesn't happen until at least 230 F ?

Is 225F still safe although very hot?

I just recently - with the help of mechanic had my cooling issue solved. There were massive air pockets in my radiator; it just had not been fully burped which I was told isn't easy to always do.

I had also changed out the t-stat and didn't have enough coolant in the engine and it heated up to 227 for about 1 minute and then I turned off the engine. Let it cool and then limped over to the mechanic with the heater on high - at about 210-215 while driving.

I understand that 227 is too hot but I don't think I "damaged it" (at least I hope) as the temp gauge didn't even blink. I then read that this Toyota gauge doesn't complain until 230+F. Assuming that is true why is that the case? Do you think I have anything to worry about?

The truck is running GREAT NOW and consistently between 185 to 197 with the AC on high and going up a hill.

 

[FordF150]

"missing shroud"


Taking off the "shroud" will definitely lead to an overheat:bluejump:

I did this in an old voltwagon. = overheat.

That is the problem here. :brick:

 

[Bad Luck]

"missing shroud"


Taking off the "shroud" will definitely lead to an overheat:bluejump:

I did this in an old voltwagon. = overheat.

That is the problem here. :brick:

Last post (before yours) was in 2014...

 

[FordF150]

Last post (before yours) was in 2014...

The original post was 2012.

So what!