hacker-pschorr

I agree putting in a colder thermostat to "fix" an overheating car is a band-aid. The idea behind running a colder thermostat is an attempt to make an already well running car run cooler.

Reason why Todd doesn't have a thermostat in either of his cars. He tries to keep his engine temp around 170 degrees.
Colder head temps is one way to try and lower / eliminate detonation.

From what I gather around here, GTS's are already prone to pinging. Trying to keep the engine as cool as possible (not just within the OEM specs) sounds like a good idea to me.

Good to know.
Those S4+ cars are unnecessarily complex

SteveG

Isn't the only purpose of a t-stat to provide for a faster warm up? I believe this is fairly important, but once it opens, and fluid goes to the rad, the t-stat is out of the picture?? and neither 83 nor 75 is going to be seen til the next start up?? Correct me please if I'm wrong.

My other question then is what is the optimum operating engine temp for the shark engine? Isn't this what you should be pointing toward, assuming the system is clean and fluid is circulating properly??? What are the factors that influence this? Airflow, OAT, RPM, rich/lean, timing/detonation? I'm a student here, but I've been told running too cool is not desired.

dr bob

The thermostat is the primary means of temperature control at all times. It opens gradually to meter water into the radiator, all with the intent of keeping the engine temps as constant as possible as load and ambient conditions change. 185º seems to be a point where the controls no longer think the engine needs to warm up more, so the factory thermostat temp seems perfect. 5-10º of coolant temp change won't make a huge difference in detonation, but 185º will allow the oil to heat up enough to boil condensation out.


In the perfect world, there's always enough radiator and fan capacity to let the thermostat do its job without going wide open. Early in the life of the car with a clean radiator, fans that always work, and an engine that runs perfectly, the thermostat doesn't need to open all the way under most conditions that us mere mortals see. Remember that the cars were exposed to extended test periods in middle-eastern desert climate during development, so the original cooling was battle-proven. Now, 20+ years later, some of that radiator and fan capacity is gone due to radiator fouling, fan malfunctions, and engine wear. We don't notice that there's any loss until we see that the safety margin is now gone, and coolant temps are higher than we are used to seeing, in situations/conditions where we regularly drive. All we need to do is restore that original cooling system capacity. We need to make sure the car is running correctly, so we aren't generating "extra" heat while doing a normal amount of work.

The radiator is the part of the system that's most prone to capacity reduction with time and miles. Internally, it suffers from deposit that accumulate in the tubes. Lack of maintenance is the primary cause, as is the use of mineral-laden water. The engine heats the water and makes it easy to hold the minerals in solution. But when there's a sharp drop in coolant temp as it enters the radiator, the minerals precipitate out, and 'plate' the walls of the tubes. Heat transfer is reduced as the minerals insulate the coolant from contact with the cold tubes. That's why we typically see internal fouling start at the bottom tubes; they are the coldest typically, since heat rises and the hot intake is at the top. And the bottom of the radiator is often receiving the most direct flow of air through the grill.

The block itself is also prone to accumulating junk, but not nearly as seriously as the radiator. There are relatively hot and cold areas of the block for instance, and we often find more precipitate in the bottoms of the block passages when we pull the drains during a cooling system service. Many have posted here that they've had to poke around the block drain holes through the crud to get the coolant to come out. That's a clue that there's a problem. That "crud" was something important at some time, or maybe it's just something that was in the water used to dilute the coolant. Hard to believe all those little rocks were poured into the system. More likely is that the minerals have been precipitated out by temp changes and the additives in the coolant itself. Certain additives like phosphates modify the pH of the coolant slightly and help the minerals drop out rather than plate out. We don't like to adjust the pH much with the aluminum, so a low-phosphate or phosphate-free coolant is often specified. Instead we depend on additives that tie up the calcium and other minerals like silica, and cause the molecules to bond to each other rather than to the aluminum. When the coolant is new and fresh, all this works pretty well. But the additives do get spent when there are lots of molecules to treat, and eventually they no longer do the job.


So: Keep the radiator and the block clean with regular coolant flushes and changes. Pull the block drains and flush the system to get the little ***** of precipitate out. Use only distilled water in your coolant mix. Use the correct coolant in the correct concentration. Don't let the system run low on coolant. Regularly, maybe coincident with timing belt changes, remove the radiator and thoroughly clean the outside. Clear all the stuff that gathers between the AC condenser and the radiator, clear all the junk that gathers in the fins, and use detergent, the garden hose, and maybe compressed air to get the outside of the fins and tubes clean as new. I used wire-ties with the ends cut blunt to push junk and bugs out of the fins; using a metal tool risks damage to tube surfaces and may bend the fins. The radiator was supported horizontally on a couple plastic saw horses so I could look down through the fins and see where there was blockage. And there was quite a bit. Push stuff out from back to front, out the way in came in.


It's supposed to get into the mid 90's today. No better chance for me to go verify that all the radiator cleaning has really paid off.

Mongo

I can only provide in detail how a 75C functions on my S4, but have not noticed anything unusual when it comes to running (after all my issues were addressed with grounds and wiring).

On cold starts, the only thing I notice is that it takes a little while longer to warm the car up. This has never really posed an issue though. As stated in my post on the first page, the 1/4 temperature mark on my gauge appears the be where the car 'operates' at when in motion. As time progresses, the car's coolant gets warmer and I notice the temperature varies between 1/4 and 1/2 on the gauge.

In stop and go traffic though, the car WILL rise to 3/4s but the radiator fans quickly suppress the higher temperatures. Temperature will linger between 1/2 and 3/4s until I am in motion at speeds above 35-40 mph, which will then drop it back down between 1/4-1/2 on the gauge.

As Hacker stated above, the idea of using a cooler thermostat is simply to make the car run cooler by opening the thermostat sooner. For the purpose of hot weather in San Diego, I put a 75C in my car. Now that I am up in the Bay Area, I supposed I could switch it back to an 83C, but I just give my car time to warm up between 1/4-1/2 temp on the gauge prior to any WOT runs.

Randy V

That describes my condition.

I cleaned the radiator fins out last year when I replaced a leaking end tank.

Looks like I need to investigate fans and airflow. I had a cracked fan shroud that I repaired to original configuration. Other than that, everything is stock and appears to be functioning correctly.

Randy V

Tom - (your post disappeared as I was writing this response)

It gets up to the third line and sometimes creeps over. Fans run continuously when it approaches that third line.

I do have an IR gun and will check the hose temp, but I'm thinking the guage is reading correctly based on the behavior of the fans.

dr bob

Randy--

Both fans running together OK? No weird squeaks, rumbling or grinding noises from the fan motors? Connections for fan power leads clean and snug at the battery?

The controller for the fans is stupid-smart, in that it will cause one fan to run at higher speed when it detects that the other has failed completely. One that's "dragging" isn't failed as far as the controller can see, so the next fan speed doesn't get used until radiator outlet temp goes up some more.

If you haven't changed it already in your ownership of the car, the rear thermostat seal can lose contact with the rear disk on the thermostat as it deteriorates. This would allow an extra portion of the circulating coolant to bypass the radiator. With the lower circulating speed of the engine in-town, and the much lower flow resistance in the bypass loop, a disproportional amount of coolant can recirculate. That might be part of the cause of the slow-is-hot, fast-is-cool symptom you describe.

I'm of the opinion that the thermostat and both seals should be replaced with every coolant hose change; for my car that's with every other timing belt change.. And "every coolant hose" means both the event and the scope of the hose change. Heater hoses, connectors to the Y-pipe from the reservoir and the front of the water bridge, the vent lines from the radiator and the water bridge, the heater valve stub connector hose, and of course the two big hoses to and from the radiator. And a new reservoir cap at the same time. I have to tell you that I hate being stranded by stupid stuff like this. I know there are plenty of cars that still have the original 25+yo heater hoses on them. And that those hoses are time-bombs that never detonate in the driveway on a day when you were planning to work on the car anyway. Nooooo... They fail on the hottest days in the most inconvenient locations, when you don't have replacements, coolant, tools, time, patience (grasshopper) to deal with them. So there.

Randy V

All good, info Doc - thanks.

I actually just replaced the thermostat, o-ring and gasket a few months ago as a PM, so it's lower on the list of suspects at this point.

Tom. M

I deleted because I read the first post...does sound like it's getting a bit toasty in a high load condition...eg. hot outside..and load on engine (a/c)... but checking the actual temps rather than relying on the gauge might give you some psychological relief...

BTW..my GT is running the 75 degree thermostat..and the gauge now never is even close to the third line...where it used to run all the time...

hacker-pschorr

You did install it spring side first.......

jthwan22

Does it help to take out the air flap assembly even if is at the open position all the time?

Mongo

Not really. Just pull the fuse and leave it open. Installed or removed makes no difference really.

Randy V

OK, screw it, based on that I'm gonna swap one in and see what happens - thanks.

D'oh! (installed correctly)

If it was installed backwards wouldn't it be constantly overheating?

depami

My Supra did this. It ran a little warmer each year until I couldn't let it idle or drive in traffic without it overheating.

Get it moving over 40 and no problem.

Nothing with the T-stat, hoses, fans or coolant helped.

Then, during T-belt change, I pulled the rad and cleaned it. I got five gallons of mayflies out of it. Haven't had cooling issues since.

OrionKhan

Randy,

Did you ever install the 75 degree thermostat? If so, did it make a difference?