80 series getting hot on slow climbs. Not cool!

[Brian Maenpaa]

A few weeks ago we drove out to Death Valley for the Super Bloom. It was over 100 degrees. We were running light. Just a big cooler full of drinks. Not loaded for camping at all.

On three occasions I pulled over on slow sustained hill climbs as the temp neared the red line and I could smell burning coolant. This was unprecedented. This engine was rebuilt by Toyota in 2021 with only 14k thus far and I replaced the radiator and hoses myself in 2019. It runs like a champ but the air con can be intermittent on really hot days (which may be related.)

Because I realize that the Toyota engineers are way smarter than me, I'm focusing on maintenance first. I bought a new thermostat to replace the original (I know) and I bought special lube for the fan clutch which has never been serviced. The threads I've read indicate this can help the fan better engage relative to the engine heat, however, I've never opened the hood and found it not spinning when the engine is running, so I'm not sure how to measure success. I mean, Are there actually times when the engine is running and the fan is not? That would be weird, right? Anyway...

I flushed the coolant last year with Toyota Red and the overflow reservoir is half full. Belts are solid. There No leaks.

I'm just think about ways to get ahead of this.

Non-OEM ideas include aux fan units (of which there are many.) And I've been bending my brain on the idea of adding a radiator by running a heater core bypass at the firewall up to a hood-mounted radiator (like the new 70-series.) Hey, the Bentley Continental has 16 radiators. Why can't I add one...

Any insight would be appreciated.

 

[Fj80oregon]

So your fan dos not spin? It has been well documented an electric fan is borderline worthless for cooling, it does help at slow speeds with the air conditioning. You need to fix replace your fan clutch it sounds like.

 

[Heckraiser]

AC cuts out at 226*, so if you've had intermittent AC issues, that's probably what's happening. Also, don't rely on the stock temp gauge it will only tell you there's a problem when it's already way hot, get a real water temp gauge with numbers on it.

I agree, fan clutch is likely the first thing to check. I modded my stock black one by adding thicker fluid and it still didn't do the job, but I bought a new modded blue fan clutch (such as offered by Landtank) and it made a big difference. When you did the radiator, did you get a stock toyota aluminum and plastic version? My truck came with the brass one and it didn't cool nearly as well as the TYC aluminum I replaced it with.

 

[Dirtygumboots]

Were you in 4-low on this slow hot climb running the motor in its power band (2800 ish RPM’s) or were you lugging it slowly up the hill with the air conditioning on and at low rpm’s? I’d consider a modded fan clutch, burping the cooling system and using 4 low to keep the rpm’s up and the fan spinning faster. Good luck.

 

[Brian Maenpaa]

So your fan dos not spin? It has been well documented an electric fan is borderline worthless for cooling, it does help at slow speeds with the air conditioning. You need to fix replace your fan clutch it sounds like.

No. It's always spinning when the engine is running, so I'm confused about what the fan clutch does. I bought some 10k lube to service it but I don't know what this accomplishes. I'll read up on it more....Thanks

 

[george_tlc]

^ there's "spinning" and then there's "moving lots of air"...
With the engine hot the viscous coupler in the fan clutch should be locking up and there's should be a LOT of air moving!

I assume the radiator has all the appropriate insulation/sealing gaskets around it to ensure air is being sucked through effectively and the shroud is in good condition etc.

cheers.
george.

 

[thedoughboy]

@Brian Maenpaa What year is your truck? This will help in determining what type of temp guage you can buy.

As others have mentioned, get a modified fan clutch, or buy a blue one and modify it yourself.

I originally put 20K in it (Blue). I still saw some higher engine temps, so I added some 40K. I'd guess the resultant mixture is ~30K. For the record my fan is always spinning.

 

[Brian Maenpaa]

AC cuts out at 226*, so if you've had intermittent AC issues, that's probably what's happening. Also, don't rely on the stock temp gauge it will only tell you there's a problem when it's already way hot, get a real water temp gauge with numbers on it.

I agree, fan clutch is likely the first thing to check. I modded my stock black one by adding thicker fluid and it still didn't do the job, but I bought a new modded blue fan clutch (such as offered by Landtank) and it made a big difference. When you did the radiator, did you get a stock Toyota aluminum and plastic version? My truck came with the brass one and it didn't cool nearly as well as the TYC aluminum I replaced it with.

Agreed. I pulled off before it even reaches the red line assuming the gauge is behind the curve. I'll look into that.
I'll take a look at the after market fan clutch. The radiator is an aluminum and plastic model from Japan, but not OEM...
Thanks for your help.

 

[Brian Maenpaa]

@Brian Maenpaa What year is your truck? This will help in determining what type of temp guage you can buy.

As others have mentioned, get a modified fan clutch, or buy a blue one and modify it yourself.

I originally put 20K in it (Blue). I still saw some higher engine temps, so I added some 40K. I'd guess the resultant mixture is ~30K. For the record my fan is always spinning.

It's a '96. I'll start with the lube service and more accurate gauge so I can get an accurate benchmark and move on to the blue clutch if I don't see an improvement. Thanks

 

[Brian Maenpaa]

Were you in 4-low on this slow hot climb running the motor in its power band (2800 ish RPM’s) or were you lugging it slowly up the hill with the air conditioning on and at low rpm’s? I’d consider a modded fan clutch, burping the cooling system and using 4 low to keep the rpm’s up and the fan spinning faster. Good luck.

No. This only occurs in 4H below 45 mph. Dropping into a lower gear and higher rpm just exacerbated the issue. Maintaining RPMs below ~2600 seemed to slow the issue, but eventually it would spike and I would have to pull over.
Last year I did a sustained 4L climb with RPMs under 2600 and the temps remained normal. Even though I was running really heavy. But the ambient temp was only ~80.
The universal response seems to be the blue clutch. Looks like I'm buying a clutch.

Thanks to everyone for taking the time.

 

[Marco Lau]

when your stock temp gauge hits 3/4, you are looking at 225 plus. F. your fan clutch is most likely the culprit. Upgrade your clutch with a blue hub or better yet, put in some 10-15k oil will help keep the temp. manageable during 4-lo or slow/heavy traffic type driving.

 

[Brian Maenpaa]

^ there's "spinning" and then there's "moving lots of air"...
With the engine hot the viscous coupler in the fan clutch should be locking up and there's should be a LOT of air moving!

I assume the radiator has all the appropriate insulation/sealing gaskets around it to ensure air is being sucked through effectively and the shroud is in good condition etc.

cheers.
george.

You know, the insulation across the top of the radiator isn't there anymore. I'll replace it. The others were installed with radiator and are still intact.
Thanks George.

 

[jonheld]

A properly setup fan clutch should be able to hold a small cat to the front grill of the truck.

Looking at the hub of your fan clutch, it appears brown which doesn't seem right at all to me.
The OEM Aisin fan clutch has a blue hub. Aisin part# FCT-004.
Also, the southwest desert folks will say that 10K clutch fluid is very weak. They usually opt for 30K.
I run 20K in mine and I'm in the northeast.

I highly recommend Rick's @landtank modified fan clutch if you don't want to mess with it.

 

[jonheld]

Lots of info in this thread:

Post in thread 'Running hot and out of ideas....'

Jun 25, 2024

Couple of things after just completing a 1300 mile road trip in 90+ degree heat. Loaded, auto climate control temp set to 75, highway temps steady at 194-198 at 65-70 mph for hours on end.

Denso is NOT the OEM for Toyota radiators. TRAD is the OEM.
Your local Toyota parts department will show 16400-66081 for the 1996 radiator, however 16400-66040 for the OBD1 FZJ80 fits as well and has better cooling capacity. That's what's in my 97 LX450 right now.
The OEM radiator cap (16401-54750 that comes with a new OEM radiator) is critical for proper cooling.
The OEM thermostat (90916-03117) starts...

• jonheld

• 

 

[LongDuck]

Has your transmission been showing any signs of slippage? I ask because that heat will be shed in the bottom of the Radiator and adds to your overall heat transfer that the Radiator has to deal with. Common knowledge is to turn Overdrive OFF and let the trans lockup to avoid slippage on slow, long climbs - or better yet, manually shift into a lower gear depending on vehicle speed so you can get RPMs up and coolant volume up.

Overheating sucks, and every time you see the needle climb, you're running at risk. Of you let it touch the red, you're really pushing it too far. You already know this, and just warning for anyone else who shows up to read later. Once in the red, you're seriously tasking the system. I ended up with a Factory Short Block after ignoring this hard won lesson...

That said, you mention your Radiator isn't OEM Mr. T - do you know who makes it? Here in AZ, we swear by OEM first or the TYC1918 Radiator that has larger tubes to flow more volume, but the same basic design: aluminum construction with plastic top and bottom tanks. These TYC1918 Radiators work well, but may not last as long as OEM, and they're about 1/2 the price of OEM, so you make your choices.

Start with the modded Fan clutch, as that will definitely allow overheating, then start looking at your Radiator and Radiator Cap. If the Cap is bad, it will bypass coolant to overflow early, and you mentioned smelling hot coolant. It's cheap insurance and easy to replace.

A new TYC1918 Radiator (*with your own foam added) would be my next step beyond the easy things,

 

[Marco Lau]

Has your transmission been showing any signs of slippage? I ask because that heat will be shed in the bottom of the Radiator and adds to your overall heat transfer that the Radiator has to deal with. Common knowledge is to turn Overdrive OFF and let the trans lockup to avoid slippage on slow, long climbs - or better yet, manually shift into a lower gear depending on vehicle speed so you can get RPMs up and coolant volume up.

Overheating sucks, and every time you see the needle climb, you're running at risk. Of you let it touch the red, you're really pushing it too far. You already know this, and just warning for anyone else who shows up to read later. Once in the red, you're seriously tasking the system. I ended up with a Factory Short Block after ignoring this hard won lesson...

That said, you mention your Radiator isn't OEM Mr. T - do you know who makes it? Here in AZ, we swear by OEM first or the TYC1918 Radiator that has larger tubes to flow more volume, but the same basic design: aluminum construction with plastic top and bottom tanks. These TYC1918 Radiators work well, but may not last as long as OEM, and they're about 1/2 the price of OEM, so you make your choices.

Start with the modded Fan clutch, as that will definitely allow overheating, then start looking at your Radiator and Radiator Cap. If the Cap is bad, it will bypass coolant to overflow early, and you mentioned smelling hot coolant. It's cheap insurance and easy to replace.

A new TYC1918 Radiator (*with your own foam added) would be my next step beyond the easy things,

totally agree - That's exactly why having that 3rd gear lockup with the custom VB is key on long hill climbs to keep the temp down....

 

[77mustard40]

My money is on the fan clutch... massive difference for me with the blue hub mod'd to open at 100* and loaded with 15K oil. I rarely crack 195* is the middle of the summer

 

[Brian Maenpaa]

Has your transmission been showing any signs of slippage? I ask because that heat will be shed in the bottom of the Radiator and adds to your overall heat transfer that the Radiator has to deal with. Common knowledge is to turn Overdrive OFF and let the trans lockup to avoid slippage on slow, long climbs - or better yet, manually shift into a lower gear depending on vehicle speed so you can get RPMs up and coolant volume up.

Overheating sucks, and every time you see the needle climb, you're running at risk. Of you let it touch the red, you're really pushing it too far. You already know this, and just warning for anyone else who shows up to read later. Once in the red, you're seriously tasking the system. I ended up with a Factory Short Block after ignoring this hard won lesson...

That said, you mention your Radiator isn't OEM Mr. T - do you know who makes it? Here in AZ, we swear by OEM first or the TYC1918 Radiator that has larger tubes to flow more volume, but the same basic design: aluminum construction with plastic top and bottom tanks. These TYC1918 Radiators work well, but may not last as long as OEM, and they're about 1/2 the price of OEM, so you make your choices.

Start with the modded Fan clutch, as that will definitely allow overheating, then start looking at your Radiator and Radiator Cap. If the Cap is bad, it will bypass coolant to overflow early, and you mentioned smelling hot coolant. It's cheap insurance and easy to replace.

A new TYC1918 Radiator (*with your own foam added) would be my next step beyond the easy things,

I couldn't remember the manufacturer until Mr. Held above jarred my memory. It is a Aisin radiator. I vaguely remember ordering OEM and being surprised that the box that arrived indicated Aisin. Apparently Aisin is an OEM supplier. Confusing... The cap is OEM. I filled the overflow tank half way and after this last trip, it seems down a pint, so I think the system is pulling and not ejecting coolant.

I read a few threads to that affect as well. The transmission has been flawless. Amazing after 275k.

Thanks for your help.

 

[ppc]

I filled the overflow tank half way and after this last trip, it seems down a pint, so I think the system is pulling and not ejecting coolant.

On a cold engine the fluid in the radiator should be at the top and the fluid level in the overflow at the cold line. Filling the overflow to half full is a mistake

 

[Brian Maenpaa]

No. This only occurs in 4H below 45 mph. Dropping into a lower gear and higher rpm just exacerbated the issue. Maintaining RPMs below ~2600 seemed to slow the issue, but eventually it would spike and I would have to pull over.
Last year I did a sustained 4L climb with RPMs under 2600 and the temps remained normal. Even though I was running really heavy. But the ambient temp was only ~80.
The universal response seems to be the blue clutch. Looks like I'm buying a clutch.

Thanks to everyone for taking the time.

As a follow-up, I'm wondering if there is an air pocket in the coolant. You mentioned burping the system. The last change I did, I first filled the block from the hose, then the radiator. Is there a best practice for eliminating air in the system?
Thanks again..