Temperature spike from mixed fluid? (1 Viewer)

[toadshade]

I was driving on the highway for two hours or so and I looked down and saw my temp gauge spiked in the red. I pulled over and popped the cap losing about three gallons of water/steam. I replaced the water and the temp came down. I got back on the road and it stayed that in a normal range so I kept driving. Every now and then the gauge would quickly spike but then go back to normal. To me it seems like air in the line. It is too fast a spike to be a thermostat issue I think. Two years ago I flushed my coolant but I never turned on my rear heater during the flush. I didn’t realize my mistake until after I turned the heater on. I did have Toyo coolant in the truck when I flushed it but changed to Prestone during the change. Is this possibly the result of the two coolants mixing? Could something be plugged? I am going to flush again and delete the heater all together but I would like to know if I should try something extra to clean out the system if i gummed it up.

 

[Kernal]

Do you have any coolant system leaks? PHH and bypass hoses replaced? Are you sure the system was full before it overheated?

Does it only overheat on long highway drives, or also around town on short drives?

First thing you might try is to remove the Thermostat then put the housing back together, ensure the cooling system is topped off, then run the vehicle under the same conditions to see if it overheats without a Tstat. Or, just replace the Thermostat (with an OEM Toyota part), top off the system, and then drive it.

Mixing two coolants may cause some sludge but IME not enough to made the engine overheat. Not completely flushing your heater cores will also not cause overheating like that. The blower motor does not have to be on when flushing, just have the HVAC temp control slider all the way over into the Red.

 

[toadshade]

No leaks. I am sure I would have seen evidence of that. Unless it just happened in a way I never detected on the drive. This was a longer than normal drive but not something unusual at all. Can’t be absolutely certain it was topped off when I left for this trip but I am pretty sure it was ok just because I put back about the same that exploded out when I removed the cap. My other “assumption” is that it is not the thermostat. The spikes in temp were absolutely immediate. The gauge would smack the upper limit and then just as quickly and randomly go back to normal. That’s why I think it is an air bubble. I would have thought a faulty gauge but my engine was definitely hot. My biggest concern was the mixed fluid. If that is not as big a deal as I thought then I am still looking for more possibilities while I am disassembling.

 

[Devils Paw 80]

I am going to flush again and delete the heater all together but I would like to know if I should try something extra to clean out the system if i gummed it up.

I would just drain it and refill, then get it up to running temperature at home and see what happens.

 

[60wag]

And don't open the cap when it is hot.

 

[fjbj40]

This it the tool I use to ensure all air is removed when servicing cooling systems. I have had it for 20 plus years of wrenching on vehicles. Always works and never had a cooling system problem after work was carried out.

Amazon product ASIN B01I40ZQWE

 

[REKCUT]

It has been discussed ad nauseam but for starters your factory gauge is little more than a dummy light. It stay "normal from about 170 to 220. You truck and and probably experiencing wide temp fluctuations and you have no indication until it lets go. 1st step would be to add some kind of true gauge. If its a ODB version of the 80 then you can get it from a simple ODB reader. If not there are multiple threads on installing a mechanical gauge. From there you can get a better idea as to what kind of activity is causing your overheating and get a diagnosis from that point.

 

[toadshade]

I thought of that. I do want to install one but as I have said, it is a spike that is noticeable and rapid. It would be as if the temperature went from 170 to 230 as fast as snapping your finger. A temperature gauge would just show that. Unless the gauge itself is bad which is unlikely since the engine was actually too hot. If it was a bubble big enough to cause that to happen and no noticeable leaks before or since it happened, then I am trying to know if there are other things that can cause this to happen.

 

[Kernal]

Oveheating is not caused by an "air bubble" in the sense you're thinking IMHO (with one exception).

IME overheating is caused by things like:

Low coolant level (most common cause of overheating IME)

Plugged or inadequate radiator for the situation (desert slow crawling)

Defective or inadequate fan clutch (shouldn't cause an issue at highway speed)

Defective thermostat

A water pump where the shaft is frozen or the vanes have worn away which is super rare IME. (If the water pump shaft was frozen you'd know it from the belts sqreeching on the pulley, before they broke)

The one exception IME to an "air bubble" is from an internally leaking head gasket (or internal crack in the block/cylinder) which can fill the cooling system with pressurized exhaust gases.

Those gases displace, or blow, the coolant out of the head/water jacket so it's the same effect as a low coolant level. The gases can't carry away the engine heat to the radiator like water/coolant does.

Whether or not the factory temp gauge jumps up in a second is irrelevant, the engine is overheating.

IMHO first thing I would do is replace the Thermostat with a new Toyota part then go from there ensuring the system is clean with a 50:50 concentration of coolant.

If you do flush the system again be sure to open the engine block drain plug during the process. If the Tstat is stuck it would help to remove the Tstat first then button up the housing before flushing.

Tip: don't hook up your garden hose to a flushing T, that can overpressurized the cooling system.

FWIW

 

[toadshade]

All the parts you mentioned are two years old or less and OEM (fan clutch, thermostat, belts, coolant (Prestone), pump and even the radiator). It is one of the reasons I was definitely looking at my installation procedure. But there really isn't anything complicated about any of that. Only thing I was worried about was the mixed coolant. But now it seems like there are two reasons that probably isn't the issue. If I have a cracked block I am going to be pissed. I am going to give it a flush, and new thermostat and see what happens.

 

[Kernal]

Just noticed that your sig indicates the 95 FZJ80 is sold, is it the HDJ80 that's overheating??

If you have a FZJ80, have you checked the PHH (Pesky Heater Hose) or the nearby Bypass hose for leaks and has either been replaced during the time you've owne the vehicle?

There are other hoses on the firewall or under the vehicle going to the rear heater which can leak and not much if anything might end up on the ground.

Get a bright flashlight and check everywhere: sides and rear of block looking from the top down and from underneath looking up. Also check underneath the floor where the rear heater lines are located ie: on the ground looking up for signs of leaks (crusty orange/pink/red/green stains).

 

[REKCUT]

I thought of that. I do want to install one but as I have said, it is a spike that is noticeable and rapid. It would be as if the temperature went from 170 to 230 as fast as snapping your finger. A temperature gauge would just show that. Unless the gauge itself is bad which is unlikely since the engine was actually too hot. If it was a bubble big enough to cause that to happen and no noticeable leaks before or since it happened, then I am trying to know if there are other things that can cause this to happen.

The temp spike you are seeing is a direct reflection from the factory gauge. It will show perfectly normal and not move at all until you get to almost 225 degrees. You can can be slowly fluctuating between 180 an 220 and It will not move. But if you reach 255 then it will spike up and usually if you get to 225 its going to keep going.


190 normal
195 normal
200 normal
210 normal
220 normal
225 spike

Install a gauge and see what kind of driving is taking it to 200 and so on.

Once again, you could be hitting 218 all the time but the one second you go to 225 your guage will "spike"

 

[SpenserAK]

If you have OBD2, a real-time gauge (scangauge, cheap wifi dongle, whatever) is a great thing to have, even with a perfect cooling system. As mentioned above, the stock gauge is a dummy, sadly. So, the real-time gauge wouldn’t “just show” a spike, it would show the slow climb you aren’t currently able to see, and then factory gauge will start jumping up when you pass a certain point where you’re already too hot.

Best of luck regardless!

 

[toadshade]

Thanks Rekut. I bet that is exactly what is happening. That makes the most sense. Now it still sounds like I have a possible issue but I am getting an external gauge and see what the temp is. So far that is a load off my mind. At least a little.

 

[REKCUT]

You have an issue for sure, but seeing what your real Temps are will help you diagnose instead of just parts changing

 

[BILT4ME]

I pulled over and popped the cap losing about three gallons of water/steam.

What on God's green earth would possess you to do this?

This is possibly the worst thing you could do.

You allow the engine to heat soak and spike because you removed all the coolant.

You run extreme risk of being severely burned.

Then you pour in cold water into a hot engine.

WTF?

 

[Kernal]

@toadshade : I noticed that your sig indicates the 95 FZJ80 is sold, is it the HDJ80 that's overheating or some other model??

 

[toadshade]

Bilt4me. I didn’t do that. Thanks for the help.