Overheating on idle

[FariZ]

Hey all, I hope you’re all doing well.

I’m posting about an issue I’ve had with my LC100 for a couple of years now.

It overheats while idling, only in the summer when though. The car doesn’t overheat while driving and cruising, AC is weak as well and the compressor needs changing.

So to start off with what I’ve replaced on the car to try to address the issue.

• Radiator
• Radiator cap
• Thermostat (I’ve tired both the petrol and diesel versions, and even tried a thermostat delete and it didn’t help)
• Fan clutch
• Fan shroud
• Fan
• Water pump
• Condenser
• The electric fan behind the grille
• Compressor

I have no idea what else could be the problem. Currently it overheats when I’m going 130KM/H as well. So I bought a new fan clutch and water pump I’m probably going to replace tomorrow.

Do any of you have any idea what could be the problem?

 

[TLCPNW]

My first thought is that you didn't fully burp the system of air. I'd start there (do you have a radiator funnel unit with the stopper?).

Search around for directions... But essentially hook the special funnel up and then get your vehicle up to temp, and then get to 3000+ rpm over and over again and you'll see air bubbling up. Ideally the front end is lifted in the air a little bit too so the top of the radiator is above all of the coolant in the system.

 

[Super77]

^ good tip to burp. Air can mess with the temp sender.

Whenever I get an odd reading, I question the source first. I would take some actual temperature measurements before throwing more parts at it. Do you have an electronic thermometer with a thermocouple attachment?

Not expensive, and you can slip the end of the thermocouple wire (the blue one shown above) into the hose connection to the radiator. It may leak a small amount during testing, but you'll get an actual temperature. You can even measure multiple spots at once with a multi-channel thermometer. This will rule out whether the vehicle is getting a bad reading - that's a different problem than actual overheating.

 

[lanierchris]

You've replaced nearly the whole cooling system and it's still hot, and now it's hot at 130 km/h too. That last part is the clue: at highway speed you have ram air and the fan is irrelevant, so this isn't an airflow problem. Either heat isn't leaving the block, or the gauge is lying to you.

How I'd work it:

1. Confirm the temp is real first. IR gun on the thermostat housing and upper hose, better yet a scan tool on the coolant temp PID. The 100 gauge is heavily damped and reads "normal" across a wide band, and a bad ECT sensor or corroded ground skews it. If actual coolant is 95-100C you have a gauge problem, not an overheat.

2. Combustion gas in the coolant. Block tester (blue fluid on the filler neck), ten minutes. A head gasket that only leaks under load pushes gas in, it collects at the high point, and you get exactly this pattern. Also watch for the overflow bottle rising after shutdown, and pressure-test cold to see if it holds.

3. Trapped air. The 100 is genuinely hard to burp. Spill-free funnel, nose up on ramps, heater full hot, run to temp and rev in cycles until bubbling stops. Do it twice.

4. Radiator flow. Aftermarket radiators vary a lot - thin cores, plugged tubes. At temp, scan the core with the IR gun in a grid; you want a smooth top-to-bottom gradient, cold patches mean blocked tubes. Same for the condenser stack, which packs full of fine sand in the desert and you can't see it from the front.

5. Fan clutch, hot, engine off: it should take real effort to spin and should stop within a turn. Plenty of aftermarket clutches never lock up at temp - this is one place the OEM Aisin unit is worth the money.

6. Retarded timing or a plugged cat both dump heat in and heat-soak at idle. A backpressure test at the front O2 bung is easy.

The thermostat delete making no difference points away from restriction and toward gauge error or combustion gas. Do the block test first, it's cheap and it either finds or eliminates the expensive problem.

 

[David310]

So I guess I will add my opinion to this matter.

Every summer, despite an entirely new cooling system my truck runs hot. On the really hot days in Phoenix I would see 225 to 230. My ac would shut off in stop and go traffic. When finally moving again my temp would only drop to 217. So at the behest of a friend we decided to juice my old blue hub with 60000csk.

My truck now runs the coolest it has during this summer and last.

I would not be afraid to really juice the clutch. I was running 24000 csk in my blue hub before.

You’re in 110–120 F weather, so some heat soak wouldn’t surprise me. These vehicles hold a lot of heat under the hood. I’d run at least 30k cSt silicone fluid in the fan clutch. There are plenty of threads on this in the 80 Series section see the quoted post.

Do you have a scanner to check actual coolant temp? Seeing 200–220 F in 115 F ambient temps doesn’t seem that crazy.

A few weeks ago I was towing about 3k lbs in 105 F weather. At 70–75 mph I saw 205–210 F on inclines with the A/C blowing warm. At a drive-thru it heat soaked around 212 F. Later, I pulled into a gas station at 210 F, popped the hood, and coolant quickly dropped to about 192 F and the A/C started blowing cold again. Heat soak gets bad when these engines are worked hard in high ambient temps and take a while to expel heat at idle.

This is on a vehicle where I’ve replaced just about everything over the 6 years and 25k miles I’ve owned it.

No issues idling in 98 F weather with 30k cSt fluid. 192.2 F max after 45 minutes and 194 F max after 117 minutes.

 

[ceylonfj40nut]

What does the front of your car look like? Big fog lights? Winch? Obstructing air flow?

 

[OEMGUY0720]

Since that looks like a full list of your cooling system all new, get yourself one of these: Head Gasket Test Kit
Do you have the 1FZ or 2UZ LC100?

 

[FariZ]

My first thought is that you didn't fully burp the system of air. I'd start there (do you have a radiator funnel unit with the stopper?).

Search around for directions... But essentially hook the special funnel up and then get your vehicle up to temp, and then get to 3000+ rpm over and over again and you'll see air bubbling up. Ideally the front end is lifted in the air a little bit too so the top of the radiator is above all of the coolant in the system.

I have burped the system multiple times.

I could be wrong though but from what I know if the system isn’t burped correctly it’d overheat even while driving and during the winter.

 

[FariZ]

^ good tip to burp. Air can mess with the temp sender.

Whenever I get an odd reading, I question the source first. I would take some actual temperature measurements before throwing more parts at it. Do you have an electronic thermometer with a thermocouple attachment?

View attachment 4202860
Not expensive, and you can slip the end of the thermocouple wire (the blue one shown above) into the hose connection to the radiator. It may leak a small amount during testing, but you'll get an actual temperature. You can even measure multiple spots at once with a multi-channel thermometer. This will rule out whether the vehicle is getting a bad reading - that's a different problem than actual overheating.

I don’t own one but I’ll check where I can buy it.

 

[FariZ]

You've replaced nearly the whole cooling system and it's still hot, and now it's hot at 130 km/h too. That last part is the clue: at highway speed you have ram air and the fan is irrelevant, so this isn't an airflow problem. Either heat isn't leaving the block, or the gauge is lying to you.

How I'd work it:

1. Confirm the temp is real first. IR gun on the thermostat housing and upper hose, better yet a scan tool on the coolant temp PID. The 100 gauge is heavily damped and reads "normal" across a wide band, and a bad ECT sensor or corroded ground skews it. If actual coolant is 95-100C you have a gauge problem, not an overheat.

2. Combustion gas in the coolant. Block tester (blue fluid on the filler neck), ten minutes. A head gasket that only leaks under load pushes gas in, it collects at the high point, and you get exactly this pattern. Also watch for the overflow bottle rising after shutdown, and pressure-test cold to see if it holds.

3. Trapped air. The 100 is genuinely hard to burp. Spill-free funnel, nose up on ramps, heater full hot, run to temp and rev in cycles until bubbling stops. Do it twice.

4. Radiator flow. Aftermarket radiators vary a lot - thin cores, plugged tubes. At temp, scan the core with the IR gun in a grid; you want a smooth top-to-bottom gradient, cold patches mean blocked tubes. Same for the condenser stack, which packs full of fine sand in the desert and you can't see it from the front.

5. Fan clutch, hot, engine off: it should take real effort to spin and should stop within a turn. Plenty of aftermarket clutches never lock up at temp - this is one place the OEM Aisin unit is worth the money.

6. Retarded timing or a plugged cat both dump heat in and heat-soak at idle. A backpressure test at the front O2 bung is easy.

The thermostat delete making no difference points away from restriction and toward gauge error or combustion gas. Do the block test first, it's cheap and it either finds or eliminates the expensive problem.

1. I just checked with the IR gun. It gives me 139° C

2. I don’t have the block tester available I’ll have to buy it and make sure. I’ll update you once I get it.

3. I have burped the system and it still happens.

4. I have bought both the condenser and radiator from the dealership. Knowing how different our climate is, I wanted to be safe and get the original from the dealership. I also clean my radiator fins every month or so.

5. Fan clutch is also original. I have made sure and it stops after one spin.

6. Timing is fine. I haven’t checked the cat though.

 

[FariZ]

You’re in 110–120 F weather, so some heat soak wouldn’t surprise me. These vehicles hold a lot of heat under the hood. I’d run at least 30k cSt silicone fluid in the fan clutch. There are plenty of threads on this in the 80 Series section see the quoted post.

Do you have a scanner to check actual coolant temp? Seeing 200–220 F in 115 F ambient temps doesn’t seem that crazy.

A few weeks ago I was towing about 3k lbs in 105 F weather. At 70–75 mph I saw 205–210 F on inclines with the A/C blowing warm. At a drive-thru it heat soaked around 212 F. Later, I pulled into a gas station at 210 F, popped the hood, and coolant quickly dropped to about 192 F and the A/C started blowing cold again. Heat soak gets bad when these engines are worked hard in high ambient temps and take a while to expel heat at idle.

This is on a vehicle where I’ve replaced just about everything over the 6 years and 25k miles I’ve owned it.

No issues idling in 98 F weather with 30k cSt fluid. 192.2 F max after 45 minutes and 194 F max after 117 minutes.

View attachment 4202975

View attachment 4202976

I’ll have to check with the silicone fluid and make sure where I can get it here.

Unfortunately I don’t have a scanner but I checked with an IR scanner and I got 139° C

I’ve had these issues for a couple of years now and I have yet to solve it.

I made an appointment with the techs at the dealership in 2 weeks. If I can’t fix it by then I’ll make them take a look and see what could be the issue and what do they suggest.

 

[FariZ]

What does the front of your car look like? Big fog lights? Winch? Obstructing air flow?

I have nothing obstructing airflow. The car is stock since when bought it from the dealer 20 years ago.

 

[FariZ]

Since that looks like a full list of your cooling system all new, get yourself one of these: Head Gasket Test Kit
Do you have the 1FZ or 2UZ LC100?

The link doesn’t ship to me but I’ll find something similar.

I have the 1FZ.

 

[ceylonfj40nut]

Engine bay pics pls showing fan clutch and shroud

 

[FariZ]

Engine bay pics pls showing fan clutch and shroud

I took multiple photos with multiple angles.

 

[OEMGUY0720]

I have no idea what else could be the problem. Currently it overheats when I’m going 130KM/H as well. So I bought a new fan clutch and water pump I’m probably going to replace tomorrow.

It “could be” something may be blocking your water jackets somewhere in the block or head why the engine is overheating even at cruising speed even with new WP, rad and thermostat.
• Check clarity of coolant see if there is contamination.
• Run a coolant system pressure test to see if it’s losing pressure (do not go higher than 15psi).