New possibility with 3fe overheating

[SciroccoDamonte]

I have been pinging ideas off of chat gpt (i know i dont trust it) but due to the fact ive replaced every component of the cooling system and im still having issues. (you can read my other posts if you want, basically the truck overheats at low rpm crawling or around town stop and go. Usually only in hotter climates like 80F and up.) Im starting to believe its something else. The cursed AI says it could be ignition timing or vacuum leak. My truck does have a pretty decent rough idle, and has for the last 17 years according to the previous owner. It does also backfire when im going downhill 25mph ish with no throttle around 1900rpm. Ive replaced the cap and rotor along with spark plugs but i do know thats only surface level stuff. Does anyone have advice on ignition timing adjustment? Its not something ive ever messed with or learned about. Additionally the engine bay of my LC gets extremely hot, to to point where any metallic surface is too hot to touch. including the hood and upper fenders. This ive tried to mitigate by putting hood spacers on, which i havent noticed them doing anything. still just trying to figure out these issues.

I do also plan on swapping in the full drivetrain from a 2000-1998 100 series from motor to T case this coming winter anyway but it would be nice to have a somewhat driveable truck until then. and if you have any knowledge on anything regarding a 2UZ swap into the 80 series I would love to hear it.

 

[jonheld]

ive replaced every component of the cooling system

With OEM parts?
Rough idle and backfire is not good. Do you have error codes?

Overheating at slow speeds points to the fan clutch.
Is your fan shroud in place? Does it have a good seal against the radiator?
Does the coolant level in the overflow rise and fall with engine temperature?
Have you cleaned out the accumulated crap that builds up between the radiator and the condenser coil?
Is the lower splash guard in place?

Rough idle is almost always associated with unmetered air entering the system. The top half of the 3FE wants to be air tight.
Air leaks can come from several places. The large intake plenum downstream of the AFM is #1 on the list.
Several spots on the valve cover including the oil fill cap gasket, the dipstick tube gasket, the valve cover grommets, the valve cover gasket, etc.

The 3FE engine bay always runs hot.

 

[Marco Lau]

can you explain more in details of the "Overheating"? what is the stock gauge indicating? Did you have coolant dumping out of overflow?? Do you have a way to tell what the temperature is indicated when overheating? aftermarket temp gauge ??

 

[SciroccoDamonte]

With OEM parts?
Rough idle and backfire is not good. Do you have error codes?

Overheating at slow speeds points to the fan clutch.
Is your fan shroud in place? Does it have a good seal against the radiator?
Does the coolant level in the overflow rise and fall with engine temperature?
Have you cleaned out the accumulated crap that builds up between the radiator and the condenser coil?
Is the lower splash guard in place?

Rough idle is almost always associated with unmetered air entering the system. The top half of the 3FE wants to be air tight.
Air leaks can come from several places. The large intake plenum downstream of the AFM is #1 on the list.
Several spots on the valve cover including the oil fill cap gasket, the dipstick tube gasket, the valve cover grommets, the valve cover gasket, etc.

The 3FE engine bay always runs hot.

Yea man OEM parts, check engine light comes on from time to time but always goes away before i can get home and read it. Ive got upgraded thicker oil in the fan clutch and a solid seal. And yes to all other questions.

 

[SciroccoDamonte]

can you explain more in details of the "Overheating"? what is the stock gauge indicating? Did you have coolant dumping out of overflow?? Do you have a way to tell what the temperature is indicated when overheating? aftermarket temp gauge ??

For sure, the needle wont ever hit the red but it will steadily climb and almost get there if im idling in a hot climate, or driving on a dirt road slowly. AKA anything lower rpm. It doesnt dump out of the overflow but it will bubble and hiss after shutoff when overly hot. I havent got around to an aftermarket gauge but i am planning on just temp gunning the radiator to make sure that at least is functioning.

 

[Marco Lau]

For sure, the needle wont ever hit the red but it will steadily climb and almost get there if im idling in a hot climate, or driving on a dirt road slowly. AKA anything lower rpm. It doesnt dump out of the overflow but it will bubble and hiss after shutoff when overly hot. I havent got around to an aftermarket gauge but i am planning on just temp gunning the radiator to make sure that at least is functioning.

Do you have a transmission cooler? I suspect your transmission temp is getting up there on 4Lo type rock crawling, and it is possible the tranny temp is affecting your coolant temp. I have had a hard time keeping my engine temp down on 4Lo type rock crawling in the summer and occasionally it would creep up to 215F ish. and that was with a Ron Davis 2 roll alum.. radiator, 20k oil in the fan clutch, sealed shroud, etc. etc. I was also on 37s and extra weight with steel bumpers, skids, sliders, etc. With the dual elec. fan conversion, my temp is finally back down to 190-200 range, much more manageable now as my fan is not RPM dependent.
The 3FE will handle overheating fairly well without compromising your head gasket given if you don't let the temp get up to 240F plus for a duration of time, however, your transmission will cook at those temp. I have overheated my tranny and it will not be as forgiven as the mighty 3F-E....
The best insurance is to install a tranny temp sender in the oil pan to monitor your transmission as well as your engine temp. an external oil cooler for the tranny is a must...

 

[SciroccoDamonte]

Do you have a transmission cooler? I suspect your transmission temp is getting up there on 4Lo type rock crawling, and it is possible the tranny temp is affecting your coolant temp. I have had a hard time keeping my engine temp down on 4Lo type rock crawling in the summer and occasionally it would creep up to 215F ish. and that was with a Ron Davis 2 roll alum.. radiator, 20k oil in the fan clutch, sealed shroud, etc. etc. I was also on 37s and extra weight with steel bumpers, skids, sliders, etc. With the dual elec. fan conversion, my temp is finally back down to 190-200 range, much more manageable now as my fan is not RPM dependent.
The 3FE will handle overheating fairly well without compromising your head gasket given if you don't let the temp get up to 240F plus for a duration of time, however, your transmission will cook at those temp. I have overheated my tranny and it will not be as forgiven as the mighty 3F-E....
The best insurance is to install a tranny temp sender in the oil pan to monitor your transmission as well as your engine temp. an external oil cooler for the tranny is a must...

I do have a transmission cooler. I am aware the 3fe is extremely robust when it comes to temperature. I have had fan clutch issues and buried the needle in the red over a mountain pass trying to get home. I do have a trans temp light in my dash and its never come on before. I have been thinking about switching to dual e fans, what did you go with for fans? Im not looking to break my bank on some summit racing or mishimoto but any suggestions are appreciated. people often mentioned aftermarket gauges so i reckon ill have to bite the bullet and get some gauges.

 

[Marco Lau]

I do have a transmission cooler. I am aware the 3fe is extremely robust when it comes to temperature. I have had fan clutch issues and buried the needle in the red over a mountain pass trying to get home. I do have a trans temp light in my dash and its never come on before. I have been thinking about switching to dual e fans, what did you go with for fans? Im not looking to break my bank on some summit racing or mishimoto but any suggestions are appreciated. people often mentioned aftermarket gauges so i reckon ill have to bite the bullet and get some gauges.

before you go down the rabbit hole, i would suggest adding 20-25k oil in the green hub and see if that improves your engine temp. Are you still running the factory radiator? The factory trans temp light comes on around 235-240f ish, so definitely not something you want to see often....The reason i would stay clear of going full elec. fans is that you will need to upgrade your factory alternator to a high output ones like 130-150 amp range as well as upgrade all big 3 wires. So there are a lot of steps involved. For the 3FE, go with some ultra slim KOSO gauges, i have 2 of them. one for the coolant and one for the transmission. Below is a pic of my coolant temp gauge....

 

[SciroccoDamonte]

I do have 15k oil in the fan but can for sure get 20-25k. I have a 4 core aluminum radiator, nothing was wrong with the factory one but as ive said ive fully replaced the cooling system trying to chase this issue. i didnt realise that requires upgraded alternator, that for sure makes it a bigger job/more expensive then id like. That gauge is sick as hell, ill look into it.

before you go down the rabbit hole, i would suggest adding 20-25k oil in the green hub and see if that improves your engine temp. Are you still running the factory radiator? The factory trans temp light comes on around 235-240f ish, so definitely not something you want to see often....The reason i would stay clear of going full elec. fans is that you will need to upgrade your factory alternator to a high output ones like 130-150 amp range as well as upgrade all big 3 wires. So there are a lot of steps involved. For the 3FE, go with some ultra slim KOSO gauges, i have 2 of them. one for the coolant and one for the transmission. Below is a pic of my coolant temp gauge....View attachment 4182386

 

[jonheld]

I do have 15k oil in the fan but can for sure get 20-25k. I have a 4 core aluminum radiator, nothing was wrong with the factory one but as ive said ive fully replaced the cooling system trying to chase this issue. i didnt realise that requires upgraded alternator, that for sure makes it a bigger job/more expensive then id like. That gauge is sick as hell, ill look into it.

IMO, you are chasing a phantom. The 3FE puts out 155 hp. I find it difficult to believe that a fully refreshed cooling system can't keep it from overheating at idle with no load, as you've mentioned.
I've driven cross country twice with my 91 FJ80 pulling a small trailer. 100% OEM cooling system and no problems.
You have an underlying issue that you're missing.
Rough idle and backfiring are telling you that. This engine should idle smooth at 650 RPM. Backfiring sounds like over fueling to me.

Some snips from the FSM:

 

[SciroccoDamonte]

Thats good info, a few of those things ring a bell. From what that says it could be off ignition timing with a fuelling issue, I’ll do some research on addressing that. I’ll rent a smoke machine to see vacuum aswell.

IMO, you are chasing a phantom. The 3FE puts out 155 hp. I find it difficult to believe that a fully refreshed cooling system can't keep it from overheating at idle with no load, as you've mentioned.
I've driven cross country twice with my 91 FJ80 pulling a small trailer. 100% OEM cooling system and no problems.
You have an underlying issue that you're missing.
Rough idle and backfiring are telling you that. This engine should idle smooth at 650 RPM. Backfiring sounds like over fueling to me.

Some snips from the FSM:

View attachment 4182831
View attachment 4182832