My car is ridiculous. Nothing making sense!!

[TravisD62]

Hey guys, my car has been having BAD overheating issues lately, all signs pointed to a BHG but I've confirmed that it's not. Oil and coolant look fine, and the test for exhaust gasses came back negative. I just ran a compression test on the car and it goes :
1 - 149
2 - 150
3 - 149
4 - 142
5 - 148
6 - 150

Now, this car has overheated extremely bad on me twice now. Yesterday it was idling in my driveway for about 5 minutes and the needle buried itself waaaaay past the red. I've noticed when I shut the car off a couple minutes afterwards the temperature is about 3/4 of the gauge. I changed my radiator cap and I thought that was the problem originally but it's still doing the same thing. I noticed there is a tiny tiny tiny crack on the top of the radiator that occasionaly leaks a bit, but barely even gets a drop of coolant out. I had it at the track yesterday with no issues at all, till a few hours after when I went to the store and let it idle. The overflow tank is always filling itself way up and spilling over and the radiator is consistently seeming empty. The fan works when the car is running, it always spins, but I've noticed when the motor is off the blades are easy to spin and I can spin them in either direction forever with no issues... Anybody have any idea whats giving me problems here? Any help would be much appreciated, thanks!

Travis

 

[kotu100]

its probably your cracked rad, any leak in a cooling sysem is bad.

 

[toyotanos]

I'd check to see if there's an air pocket in the engine, as well as changing the thermostat out for a brand new OEM one. $30 from the dealer with a new gasket. They're the first things I do when checking for an overheating problem.

You can also take a look in the radiator to see if any of the tubes are blocked or if the fins outside are covered in leaves/cottonwood/bugs. Start with the basics!

 

[Devin LeBlanc]

Compression checks don't always tell you what you need to know. You need to do a leak down test and see if you have any to the cooling system

 

[SideWinderGX]

Lets say you give the fan a good spin, how long does it freewheel for?

 

[TravisD62]

Do you really think that little crack would affect the cooling system that much? I guess this cars finicky but damn! If I spin the fan it goes for a few seconds, probably 2 full rotations? It engages always when the motor is running, which is the weird part to me... I spun the fan on my dads 94 2JZ and I know it's not the same motor, but the fan felt identical to his.

 

[IJ.]

Tiny crack = can't pressurise so it's going to overheat/boil...:nono:

The 7M cooling system is so damn finnicky you're playing Russion Roulette by driving it.

 

[mk3_7m]

I had the same problem last time. When driving my temp gauge would randomly spike over the top. Changed radiator, temp sensor, thermo stat and everything was still the same.
This was a rebuilt engine as well.

Changed the water pump and the problem stopped. I compared the water pump with the other one I had with my last engine, one blade was made out of stainless steel and had a better flowing wheel, the one I took out was made out of cast iron and didn't look like it would flow as good. It may not be the problem but it fixed it for me.

 

[jetjock]

Egypt. Nuff said...

 

[jdemara]

Do what I did, and never worry about it again! Got brand new Mishimoto radiator (direct replacement fits right in!), rebuild the fan clutch (empty and fill with fluid - theres a write up on it), new fan shroud, New thermostat and gasket, ALL new coolant hoses (even the ones to the turbo, back of the head, to the throttle body etc). Do a pressure check on the cooling system to make sure its holding. Flush it. Fill it and make sure there are NO air bubbles.
Couple hundred bucks to do this properly for the rad, and hoses etc.. but its worth it, and it needs to be done eventually anyways if you want a reliable Supra.

 

[suprarx7nut]

You know you need a new radiator. Don't drive it until you get a radiator. Autozone grand or oem, or aftermarket aluminum. Anything.

You might have other problems, but you need a good radiator first.

Don't use any bull shit "stop leak" either. That stiff should only be used if you're in the middle of Africa and desperate...


Sent from my ADR6400L using Tapatalk

 

[Dirgle]

IJ pretty much had the solution, you should listen to him. The boiling point of water increases as you raise the pressure.

The boiling point of water at sea level is 212F.

The boiling point of water in radiator with an 18psi cap at sea level is 255F.

The radiator needs to hold pressure or the coolants capacity to remove heat from the engine is greatly reduced. I would also bet your radiator cap is in need of replacement and not holding pressure based on how often the overflow tank is overflowing itself. And note that auto part store radiator caps are really crappy. I had to go through three auto zone radiator caps before I found one that held pressure properly. Fix the radiator crack and replace the cap, then make sure the hose going to and down inside the overflow tank is in good working order. If not, the system has no way of properly getting the air out.

 

[TravisD62]

Well, I ordered radiator hardpipes, a new thermostat, gaskets, all new hoses, an oem rad cap, and picked up some new Toyota coolant and a flush kit. I would really rather not replace the radiator right now as I'd like to get a PWR replacement in the winter, but shipping time and cost would better suited for then. Is it crucial I get a new radiator asap? The crack doesn't leak for the majority of the time and it's honestly insanely tiny - like barely even a pin hole. I have a plastic radiator patch kit that puts a new piece all the way over the crack, and isn't just a tube of sealant. Would this hold me over for another month or two? If not I understand, and can order a new rad as well, but I only drive the car a few times a week and have a reliable Civic as my DD. I love this car to pieces, but I'm also a medical student and it honestly makes me sick to my stomach looking at my bank statement from the last few months. Oh the joys of modifying a 23 year old car...... LOL.

---------- Post added at 11:36 PM ---------- Previous post was at 11:28 PM ----------

IJ pretty much had the solution, you should listen to him. The boiling point of water increases as you raise the pressure.

The boiling point of water at sea level is 212F.

The boiling point of water in radiator with an 18psi cap at sea level is 255F.

The radiator needs to hold pressure or the coolants capacity to remove heat from the engine is greatly reduced. I would also bet your radiator cap is in need of replacement and not holding pressure based on how often the overflow tank is overflowing itself. And note that auto part store radiator caps are really crappy. I had to go through three auto zone radiator caps before I found one that held pressure properly. Fix the radiator crack and replace the cap, then make sure the hose going to and down inside the overflow tank is in good working order. If not, the system has no way of properly getting the air out.

I just replaced the cap and it seems to be holding pressure, when the motor is warm and I squeeze the upper rad hose it's holding pressure and not budging. Hose to the overflow bottle also seems to be okay, I cleaned it out and checked it over. Sorry if my reasoning sounds overly basic, but I'm no expert with cars. If the radiator is consistently low on coolant, and the overflow bottle is always full and occasionally overflowing, the system is letting fluid out when it's hot, but not allowing any back in when it cools off right? The system is unable to build enough vacuum pressure to force coolant back through, so is this causing air pockets in the cooling system, or is the car simply just running on too little coolant? Again I apologize, but I'm having a hard time wrapping my head around what's causing the problem, if this is the case then a thermostat or plugged radiator would almost be negligible when trying to find the problem because it's unlikely either part would cause a loss in vacuum pressure right?

 

[jdemara]

I had the SMALLEST hairline crack in my rad a few years ago that could only be seen if you flex or bend the upper hole for the hose. Caused all kinds of weird overheating and temp spikes. Also, overflow would sometimes fill up, and sometimes not. If you dont want a big head gasket job with a big price tag, spend the couple hundred bucks for a new radiator sooner than later. You'll be happy you did it. The coolant should always be full inside the radiator when you check it, if not, you are either losing it out the overflow, a leaking hose, through a blown headgasket... etc

 

[TravisD62]

Alright then, I'll order a new rad right away! I guess in the meantime I can finally get the build thread going for it! Been meaning to get on that for over 2 years now, hahaha.

 

[jdemara]

http://store.driftmotion.com/static/i-mmrad-sup-86.php

Thats the rad I bought. Love it, fits perfect. I would recommend it if you want a direct fit replacement, and a LOT better cooling capacity. But that being said, search around and see what you like best.

 

[Dirgle]

Well, I ordered radiator hardpipes, a new thermostat, gaskets, all new hoses, an oem rad cap, and picked up some new Toyota coolant and a flush kit. I would really rather not replace the radiator right now as I'd like to get a PWR replacement in the winter, but shipping time and cost would better suited for then. Is it crucial I get a new radiator asap? The crack doesn't leak for the majority of the time and it's honestly insanely tiny - like barely even a pin hole. I have a plastic radiator patch kit that puts a new piece all the way over the crack, and isn't just a tube of sealant. Would this hold me over for another month or two? If not I understand, and can order a new rad as well, but I only drive the car a few times a week and have a reliable Civic as my DD. I love this car to pieces, but I'm also a medical student and it honestly makes me sick to my stomach looking at my bank statement from the last few months. Oh the joys of modifying a 23 year old car...... LOL.

---------- Post added at 11:36 PM ---------- Previous post was at 11:28 PM ----------



I just replaced the cap and it seems to be holding pressure, when the motor is warm and I squeeze the upper rad hose it's holding pressure and not budging. Hose to the overflow bottle also seems to be okay, I cleaned it out and checked it over. Sorry if my reasoning sounds overly basic, but I'm no expert with cars. If the radiator is consistently low on coolant, and the overflow bottle is always full and occasionally overflowing, the system is letting fluid out when it's hot, but not allowing any back in when it cools off right? The system is unable to build enough vacuum pressure to force coolant back through, so is this causing air pockets in the cooling system, or is the car simply just running on too little coolant? Again I apologize, but I'm having a hard time wrapping my head around what's causing the problem, if this is the case then a thermostat or plugged radiator would almost be negligible when trying to find the problem because it's unlikely either part would cause a loss in vacuum pressure right?

This is a good observation, the system not drawing the coolant back in to the radiator from the overflow is a sign the system is not sound and not holding pressure. Start with the simplest or most obvious solutions first. You know the radiator has a crack in it. So get your PWR radiator now or accept that you are going to need an interm solution and get the radiator repaired or replaced. Deal with this issue first so that if the overheating issue persists you don't have a cracked radaitor impeading the troubleshooting process, potentaily causing you to spend more money on the problem than is necessary . Also remember that as materials go through heating cycles that they expand and contract. Every time you heat cycle that radiator the crack is going to grow.

 

[planemos]

If you are getting a "waterfall" type of sound coming from under the dashboard then it could be your heater core. My car had very similar symptoms as yours. My Supra had a blown head gasket a long time ago before I was the owner. It got fixed but I think it also caused the heater core to crack. And I live in BC it is quite similar temps and weather as you.