80 Operating Temperature per FSM (1 Viewer)

[SUMOTOY]

Mr. T confirms 'normal' operating temps as 203F +/-23F (correction to my previous posts of 202 +/-22) a couple ways in the FSM

Engine temp A/C cutout spec = 226F
Thermostat opening temp spec = 180F
Thermostat fully open temp spec = 203F --- Ideal closed loop engine temperature

The last figure (spec found in FSM EG334 = min spec - 10mm Lift at 203F)) is signiicant to those tweeking radiator fans and/or VC clutches, mechanical or electric. If you tweek the fan clutch to lock up before 203F, your thermostat isn't fully open! Which means exactly, you are using engine power to fight thermostat control. Very inefficient engine heat management I say.

I run into this a lot with the cars that I work on using electric fans. The fully open spec of the thermostat is key to mechanical or eletric fan control. Normally, fans operate in full lockup (or 100% voltage) at ~5 degrees above fully open thermostat spec. If you engage a fan before the thermostat is fully open, you are wasting engine fan load to fight thermostat control. In Audis, there are some 10 flavors of radiator fan temp senders (electric), and 5 or so flavors of thermostats. What I see all the time, is the installed thermostat rated higher than the fan switch. In electrics this can lead to dead batteries. In mechanicals, it's just robbing engine power and efficiency to fight thermostat coolant temp control.

I might go on to say, if you have a thermostat that is less than fully open, you have effectively reduced the cooling efficiency of coolant. Could it be this affects #6 cylinder first where maximum cooling exchange is needed most?

Specific to the mechanical fan in the 80, the target temp for full lockup should be around 210. Like at 100C? More specifically, if you are targetting a lower temp than 203F for mechanical lockup engagement, you should run a cooler thermostat.

Some FSM food for thought that targetting 'cooler' engine operating temps isn't necessarily better.

Scott Justusson
94 FZJ80 Supercharged

 

[turbocruiser]

Something is somewhat wrong with this; I have to push and push and push my rig to get to 100 celcius this is with an unmodified brand new blue clutch, stock fan, stock thermostat, etc. Same thing with the old clutch, same thing with the old thermostat, etc. The rig seems to want to run at about 88 to 92 degrees almost 100% of the time. I think it is a leap to say that the rig should run with fully open thermostat, if that were the case, why not make the thermostat a flapper design where it is full open or full closed and not the type that opens and closes gradually and rarely fully?

 

[landtank]

Looks to me that anything above 203* is overheating. The thermostat is wide open and the truck is still getting hotter.

 

[cruiserdan]

Something is somewhat wrong with this; I have to push and push and push my rig to get to 100 celcius this is with an unmodified brand new blue clutch, stock fan, stock thermostat, etc. Same thing with the old clutch, same thing with the old thermostat, etc. The rig seems to want to run at about 88 to 92 degrees almost 100% of the time. I think it is a leap to say that the rig should run with fully open thermostat, if that were the case, why not make the thermostat a flapper design where it is full open or full closed and not the type that opens and closes gradually and rarely fully?

Could it be a result of the location of your temp sender?

 

[cruiserdan]

Looks to me that anything above 203* is overheating. The thermostat is wide open and the truck is still getting hotter.

Then why does the A/C not cut out until 226?

I'm not trying to be combative here Rick, just wondering out loud.

 

[landtank]

I don't know Dan. My understanding is that the thermostat is supposed to regulate the engine's temperature. If that thing is wide open at 203* and your running higher than that then the system to me is overwhelmed. If Toyota wanted it to run hotter than they would have put in a higher temp T-Stat.

I'm just taking a simpletons look at the cooling system and ignoring what is being done for the AC system. I read somewhere here that the 226* shutoff point was actually there to protect the AC system and not indicative of being engine related. My understanding is that as the temp increases so does the pressure in that system and 226* was the chosen limit.

 

[cruiserman]

I would say that cyl #5 is the hottest, not 6.

At what temp does the fan clutch lock up? Perhaps it's re-engaging at 203 and above. I don't think the AC cutout protects the AC system. It prevents the condensor from dumping more heat into a nearly overheated engine.

 

[-Spike-]

The A/C cuts out as a safety, last-ditch effort to protect the engine. To say the the truck was intended to run at this range is false, IMO. Also, the t-stat should only be fully opened if the cooling system is at it's extreme limit, not as a normal occurance for extended periods. I refuse to believe the cooling system was designed to operate at it's limits, with no consideration for adverse conditions, i.e; with no headroom or ability to take out more heat energy than it would normally see. I can't see them designing the cooling system to run at more than 75% of capacity normally, if even that.

-Spike

 

[SUMOTOY]

I don't know Dan. My understanding is that the thermostat is supposed to regulate the engine's temperature. If that thing is wide open at 203* and your running higher than that then the system to me is overwhelmed. If Toyota wanted it to run hotter than they would have put in a higher temp T-Stat.

Accepted theory is that primary engine temp function is a closed loop thermostat system. Above WOT (wide open thermostat) nothing is "overwhelmed", temp just becomes regulated (augmented) by the fan circuit. Ideally, the wide open thermostat stays wide open all the time, life is good, engine is operating inside the coolant (engine temp only) closed loop system. A higher load inducing variable will push that temp above a wide open engine thermostat, which then means engine temp is controlled by the engine fan system (specifically the engine coolant control goes open loop).

A lower load (vs ideal) will cause the thermostat to begin to close, which decreases cooling efficiency in an attempt to bring the temp back up to target. The *problem* comes when folks try to override the closed loop cooling control (engine temp) with a open loop compensation (engine fan). You have an engine thermostat closing to bring temps back toward ideal, and a fan thermostat working harder to overcome that closed loop cooling inefficiency. Neither is smart enough to know what t'other is doing. This is true in mechanical and electric setups.

I'm just taking a simpletons look at the cooling system and ignoring what is being done for the AC system. I read somewhere here that the 226* shutoff point was actually there to protect the AC system and not indicative of being engine related. My understanding is that as the temp increases so does the pressure in that system and 226* was the chosen limit.

I don't agree with this statement at all. The A/C pressure switch shutdown *pressure* is 412psi, and turns back on at 327spi. In my ABC Cooling Part I, R134a at 412psi = 186F, R134a at 327psi = 167F. So, A/C pressure(temp) shutdown is independent of engine temp shutdown. Specifically, a 226F condenser temp could never be reached without pressure switch intervention, or compressor failure.

Understanding that, I propose that the 226F is to reduce the heat exchange load on the radiator only, and has nothing at all to do with R134a pressures or temps. And in fact, you routinely can have engine temp A/C cutoff with ideal 134a temps/pressures.

I believe the FSM is pretty clear in terms of what Mr. T targets for ideal temps in the closed loop thermostat temp circuit. I also believe that lowering the open loop threshold for fan intervention, is not good for engine heat management efficiency.

Scott Justusson
94 FZJ 80 Supercharged

 

[cruiserdan]

Understanding that, I propose that the 226F is to reduce the heat exchange load on the radiator only, and has nothing at all to do with R134a pressures or temps.

Absolutely.

 

[SUMOTOY]

Guys and gals:
My posts are only addressed at tweeking the open loop portion (fan intervention) below the wide-open engine thermostat threshold. Specifically, *if* you want to choose this fan intervention avenue over what Mr. T dictated (203F), a lower *engine thermostat* would give better engine efficiency to that mod.

You can propose that primary (closed loop) engine thermostat function has a temp range of 180-203, and that secondary (open loop) engine fan control has a temp range of 203-226 (terciary control above 226 = A/C shutdown and radiator pressure release). Mr. T. then defines primary ideal closed loop operation of the 1FEFZ as installed in the 80 as 203F. By definition of the primary (engine) cooling circuit, below 203F tenps you have too much cooling capacity (thermostat then intervenes to add thermal load), and above 203F temps you don't have enough cooling capacity (radiator fan intervenes to add thermal capacity).

THEN, it follows....
Low
Below 203F the closed loop system restricts flow > reduces cooling efficiency vs ideal temp. Above 203F the open loop system (fan intervention) increases cooling efficiency (overcapacity) vs ideal temp. Above 226 electronic control decreases cooling load vs ideal temp.

HTH

Scott Justusson

 

[Epic Ed]

Good info, guys. So how, then, would you propose improving the efficiency of the AC condensor at low speed/idle? In my 4Runners, there is an electric fan in front of the radiator that runs during low air-flow situations, and this keeps my AC temps cold as ice even if I'm idling along for more than an hour in rush hour traffic in the middle of the summer with temps exceeding 110 outside. I don't get this with my Cruiser. The AC works, but it's clearly not as efficient at low speed/idle as it is when moving. I had considered installing an electric fan to improve the output, but it sounds like I'd be walking a fine line between making the AC more efficient and making the engine cooling less efficient. Suggestions?

Ed

 

[LandCrusher'70]

Good info, guys. So how, then, would you propose improving the efficiency of the AC condensor at low speed/idle? In my 4Runners, there is an electric fan in front of the radiator that runs during low air-flow situations, and this keeps my AC temps cold as ice even if I'm idling along for more than an hour in rush hour traffic in the middle of the summer with temps exceeding 110 outside. I don't get this with my Cruiser. The AC works, but it's clearly not as efficient at low speed/idle as it is when moving. I had considered installing an electric fan to improve the output, but it sounds like I'd be walking a fine line between making the AC more efficient and making the engine cooling less efficient. Suggestions?

Ed

An Aux. fan in front of the A/C condenser.

I too have been following these 'cooling' threads for a long time. Very good info. Tons of it. Just have to sift through all the info and figure out what is best for my (or your) application.

Good stuff.

 

[landtank]

by running the truck in wide open Thermostat the flow of coolant would be at it's highest rate. Now according to Robbie, Toyota engineers explained that one of the changes to the new style HG was to reduce the size of the holes to slow down the flow rate to improve the rate of heat absorbsion. Any ideas out there on how higher flow rates might cause hot spots or other heat related problems within the engine?

 

[cary]

I believe that Sumotoy is absolutely right in theory. The one thing that we are missing is how the engine temperature read by the temp gauge corresponds to the temperature at the thermostat? There could be a 10F+ difference between the two.

Also, keep in mind, for many people the issue is not keeping the engine running at 190f all the time (which I believe is an unrealistic goal), but to keep it from running at 210f+ in hot weather. At this point the thermostat should be clearly open all the way and you are dealing with the open system issue on how to remove heat from the closed system.

 

[SUMOTOY]

Epic Ed:
Search ABC's of 80's Cooling, or ck FAQ = Aux Fan for cooling Condenser and hookup is Part I-III

Landtank:
The smaller holes will indeed slow down the coolant, but I'd sure like to see where that actually makes a difference to HG failure. It's really tough for that fix to be the cure all, especially in an engine driven water pump where flow is an engine rpm variable. Specifically, a wide open thermostat coolant flow rate is massively different at 800rpm vs 4800rpm. If these are universally equal smaller holes in the head gastket, that revision might address #5 and #6 at a given flow rate, but likely at the expense of increased temps at #1-4 at that same flow rate. Ideally, if working with a headgasket on a long inline engine (water pump at front), the holes will be larger in the front, and smaller in the back. That's not an ideal for production costs (read: hence the universal hole size #1-#6)

A better way to address this problem is to add water ports to each cylinder, or at least to the rear cylinders. This is a pretty common fix on the 2 valve long Audi I5 engines (add water ports to the head at 4&5), and the later production 4V heads used a 5 port water manifold. The problem with long inline motors is equal cooling of the cylinders vs production costs of doing a more ideal 'unequal' cooling of individual cylinders.

Cary:
We certainly can say that Mr. T believes the 80 design is at heat exchange equalibrium at 203F. Yes it is in theory, yet application is a series of compromises. In mechanical driven fans, there is more overlap of ideal temp vs (secondary) open loop operation. This really has to do with how quickly temp spikes can happen, and the reaction time of the temp circuits. Especially one that isn't based on engine temp directly (VC clutch).

My own goals and targets have always been to get to 100C (212F) and then have an overabundance of secondary cooling capacity to stay at that temp. This is the way Audi chose 20 years ago, and it's still in their engineering today. One of the main reasons I want to get the VC fan out of my truck. It's speed variable output is what makes it less than ideal. The advantage to electrics is exactly that fan efficiency is a constant in the open loop cooling circuit. And it's operation can be tied directly to engine temp vs engine bay temp (read: active vs reactive secondary cooling circuit).

Scott Justusson

 

[landtank]

It's really tough for that fix to be the cure all, especially in an engine driven water pump where flow is an engine rpm variable.

That's my whole point, it isn't a rpm variable at all, it has to do with how open the T-Stat is. All the RPMs in the world won't yield any flow with a closed T-Stat.

 

[SUMOTOY]

That's my whole point, it isn't a rpm variable at all, it has to do with how open the T-Stat is. All the RPMs in the world won't yield any flow with a closed T-Stat.

Sure it will Rick, the coolant just doesn't get directed thru the radiator, there is definitely flow thru the block and head! It's just the closed loop circuit is bypassing the radiator when the thermostat is closed. Once it's open, it flows thru the radiator.

Scott Justuson

 

[SUMOTOY]

Guess at any road speed that forces more air through the radiator than the fan does is a bad thing cause there is exess 'open loop' cooling.

Not at all. Road speed (ram air increases) just changes the coolant temp, which then changes the thermostat opening. So, if road speed increases to the point where you have more excess cooling capacity, the thermostat will close.

However, if engine load increases as ram air speed increases, so the equilibrium is 203F, you have ideal heat exchange again. If engine load increases beyond the ram air added cooling capacity, the open loop (fan intervention) becomes the temperature control.

ST

 

[cary]

Just to note that the future of the cooling is coming. BMW in their new generation engines has gone to electric WATER pumps. The advantage is that they can get max cooling at low speed where needed, but minimize drag at higher speeds where it isn't.