Overheating again...

[JJ994runner]

Since you're saying it's getting worse I'm guessing it didn't start right after the engine rebuild? You also say that it's happening with strain on the engine so if you are cruising down the highway it's fine? If so my guess would be fan clutch not engaging, at least not enough under slower speeds with strain.

So it was overheating right before it got rebuilt but I’m guessing that was because the water pump went out and a head was cracked but that could have been caused by the car overheating after the water pump went out.

 

[spartacus]

Yea my fan roars when I start it up and like you said then fades away I also checked by spinning the fan while it was cold to see if it would free spin and it didn’t.

Radiator cap not holding pressure? I dont trust the Auto zone radiator but at this point before you start throwing more parts at it. Do a compression test on the motor to rule it out.

 

[Bad Luck]

I have a 1999 4runner 3.4l that I have been having overheating problems with. At first it was only when I would climb up steep dirt roads but it is starting to happen daily driving with any sort of strain on the motor uphill. I replaced the radiator and the thermostat and burped the coolant but none of that helped. The motor was also rebuilt about 15,000 miles ago.

Looking for some suggestions as to what the solution could be.

How are you monitoring your engine coolant temps? What brand thermostat did you use? What position was the jiggle valve?

 

[gamefreakgc]

Hmm, this is a puzzler. If the temp gauge on your dash really is going up, it's hot hot hot. 3/4 of the way up is around 230-240 degrees.

So this is what we know:

1. New radiator (autozone radiators are fine, I've used them)
2. New water pump
3. New thermostat
4. Motor rebuild (overheated before rebuild)
5. Fan clutch appears fine

You've changed the 3 main components of the cooling system. It's a very simple system where the water pump circulates fluid and the thermostat controls the flow. Radiator cools the fluid. So at this point the most likely causes would be lack of pressure allowing the coolant to boil, or a failed "bad out of the box" part. Most part stores will have a coolant system pressure test kit you can borrow for free, I would start there and see if it holds pressure. If it doesn't you'll either see a leak or hear hissing noises.

A brand new OEM radiator cap wouldn't hurt at this point. If you need your vehicle to drive ASAP, you can swap thermostats with a 170 degree or 180 degree thermostat instead of the stock 190. It won't keep it from overheating but will help it cool down quicker once you get up to speed.

 

[JJ994runner]

Hmm, this is a puzzler. If the temp gauge on your dash really is going up, it's hot hot hot. 3/4 of the way up is around 230-240 degrees.

So this is what we know:

1. New radiator (autozone radiators are fine, I've used them)
2. New water pump
3. New thermostat
4. Motor rebuild (overheated before rebuild)
5. Fan clutch appears fine

You've changed the 3 main components of the cooling system. It's a very simple system where the water pump circulates fluid and the thermostat controls the flow. Radiator cools the fluid. So at this point the most likely causes would be lack of pressure allowing the coolant to boil, or a failed "bad out of the box" part. Most part stores will have a coolant system pressure test kit you can borrow for free, I would start there and see if it holds pressure. If it doesn't you'll either see a leak or hear hissing noises.

A brand new OEM radiator cap wouldn't hurt at this point. If you need your vehicle to drive ASAP, you can swap thermostats with a 170 degree or 180 degree thermostat instead of the stock 190. It won't keep it from overheating but will help it cool down quicker once you get up to speed.

I will run and do that and get back to you on what I find out I did get my thermostat from autozone as well because my Toyota wasn’t open at the time so that could be a problem not sure.

 

[19963.4lsr5]

I’ve never got a bad t-stat from a parts store. Mine always failed a few years later by not letting the engine get up to temp.

If you’re only overheating under load and everything was replaced......only overheating under load to me is a head gasket.

My new clutch fan is loud AF for over 1 min. My bad one that wouldn’t keep the AC cold got quiet in less than 30sec.


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[Endlessblockades]

I didn't read the entire thread but do you have access to a simple OBDII reader to get an accurate temp? Autozone. etc. may loan you one. Is your coolant really boiling? It would be good to see that the temp is headed towards with a real gauge. Sorry if I missed that info in the thread.

 

[JJ994runner]

Hmm, this is a puzzler. If the temp gauge on your dash really is going up, it's hot hot hot. 3/4 of the way up is around 230-240 degrees.

So this is what we know:

1. New radiator (autozone radiators are fine, I've used them)
2. New water pump
3. New thermostat
4. Motor rebuild (overheated before rebuild)
5. Fan clutch appears fine

You've changed the 3 main components of the cooling system. It's a very simple system where the water pump circulates fluid and the thermostat controls the flow. Radiator cools the fluid. So at this point the most likely causes would be lack of pressure allowing the coolant to boil, or a failed "bad out of the box" part. Most part stores will have a coolant system pressure test kit you can borrow for free, I would start there and see if it holds pressure. If it doesn't you'll either see a leak or hear hissing noises.

A brand new OEM radiator cap wouldn't hurt at this point. If you need your vehicle to drive ASAP, you can swap thermostats with a 170 degree or 180 degree thermostat instead of the stock 190. It won't keep it from overheating but will help it cool down quicker once you get up to speed.

Just did a pressure check on my coolant system pumped it up to 15 psi and couldnÂ’t find any leaks from the water pump or any of the hoses or anything it also held pressure except it maybe drops half a psi after letting it sit for 15 minutes.

 

[JJ994runner]

I didn't read the entire thread but do you have access to a simple OBDII reader to get an accurate temp? Autozone. etc. may loan you one. Is your coolant really boiling? It would be good to see that the temp is headed towards with a real gauge. Sorry if I missed that info in the thread.

All I have is one of the FIXD obd2 sensors but I can go rent one from autozone and try it out to check if the temperature really is getting hot.

 

[JJ994runner]

I’ve never got a bad t-stat from a parts store. Mine always failed a few years later by not letting the engine get up to temp.

If you’re only overheating under load and everything was replaced......only overheating under load to me is a head gasket.

My new clutch fan is loud AF for over 1 min. My bad one that wouldn’t keep the AC cold got quiet in less than 30sec.


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Would the cooling system be able to hold pressure if I had a bad head gasket?

 

[Bad Luck]

Would the cooling system be able to hold pressure if I had a bad head gasket?

Are you doing the pressure testing with the engine cold? If you aren't, then you should be. Cooling system pressure will decrease on it's own if the engine is warm due to components cooling off.

And yes, it's possible the head gasket could have a small leak and still hold that pressure.

 

[JJ994runner]

Are you doing the pressure testing with the engine cold? If you aren't, then you should be. Cooling system pressure will decrease on it's own if the engine is warm due to components cooling off.

And yes, it's possible the head gasket could have a small leak and still hold that pressure.

Engine was cold while I was doing the test.

 

[19963.4lsr5]

Are you doing the pressure testing with the engine cold? If you aren't, then you should be. Cooling system pressure will decrease on it's own if the engine is warm due to components cooling off.

And yes, it's possible the head gasket could have a small leak and still hold that pressure.

I agree that it could be bad and not show up in a test cold.

As you get into the throttle the combustion pressure increases. Which can push its way through a failing (not blown) head gasket.

A leak down test with a hot engine and rad cap off may or may not reveal it because the highest pressure you can use is 120psi.


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[plcfcng]

There is a test that can be done if you have a blown head gasket. If you go to a shop they can take a gas sample of the radiator to tell if there is combustion gases are in the cooling system. If you are hitting your head against a wall the test could be worth it. Call and ask for a price at a local shop this can help you decide on what to do next. If this turns out negative then I think it would be a flow problem like something plugged up or something weird like that.:yo:

 

[19963.4lsr5]

There is a test that can be done if you have a blown head gasket. If you go to a shop they can take a gas sample of the radiator to tell if there is combustion gases are in the cooling system. If you are hitting your head against a wall the test could be worth it. Call and ask for a price at a local shop this can help you decide on what to do next. If this turns out negative then I think it would be a flow problem like something plugged up or something weird like that.:yo:

I bought the napa test kit. I think I paid 50-60 dollars for it. The fluid has a shelf life though.


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[t3rr1ck]

I have a 97 3rz-fe, the truck temp gauge on my dash rose to 3/4 on a long hill. Coolant was topped up and had replaced t-stat a month earlier. She rose to 3/4 on 2 other occasions but no higher. I only drove for 5 minutes max at the 3/4 mark before pulling over. Takes a good 45 minutes of idle or driving to notice. Any thoughts? Stumped asf..

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[Endlessblockades]

I have a 97 3rz-fe, the truck temp gauge on my dash rose to 3/4 on a long hill. Coolant was topped up and had replaced t-stat a month earlier. She rose to 3/4 on 2 other occasions but no higher. I only drove for 5 minutes max at the 3/4 mark before pulling over. Takes a good 45 minutes of idle or driving to notice. Any thoughts? Stumped asf..

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Don't take this the wrong way, but get a temp gauge that reads actual engine coolant temp data from the ECU. The dash gauge on these is dangerously inadequate. Mine never went over "1/2" under any conditions and I found I was running 212 degrees with a $35 OBDII plug-in gauge. "3/4" could mean nothing or be a potentially serious situation.

 

[phattyduck]

I have a 97 3rz-fe, the truck temp gauge on my dash rose to 3/4 on a long hill. Coolant was topped up and had replaced t-stat a month earlier. She rose to 3/4 on 2 other occasions but no higher. I only drove for 5 minutes max at the 3/4 mark before pulling over. Takes a good 45 minutes of idle or driving to notice. Any thoughts? Stumped asf..

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Get a new OEM radiator cap.

-Charlie