5.7 Running hotter than usual.

Starting talking about this in another thread related to towing however this seems to have less to do with towing.

lately my truck has started running at idle around 197deg and climbing as high as 207deg while driving around town unloaded but up hills. For reference it’s only mid 60’s ambient here.

I recently drive 300 miles across the state at 75mph the truck ran about 200-202deg.. on the way home I was towing a 3500lb trailer and it ran about 197-200deg

I never paid too close attention but From what i remember before the truck ran 185 and was extremely consistent.

I noticed this fluctuation after replacing the tstat, I did burp it and reinstalled the old tstat to rule that out. Replaced the rad cap, which made no change.

I also tested the fan clutch, at engine temps of 185 I can stop the fan while the engine runs but at engine temps in the 195 range the fan runs stronger. So I think the fan clutch is getting weak, but would this really make a difference on the highway?

Truck has 171k miles never had any issues, water pump was replaced maybe a year or two ago. Can’t see any leaks around it.

 

That all sounds normal to me, with the exception of the 207 driving around town. Mine will consistently hit 203 if it's working harder, and otherwise stay between that and 190 or so. The 207 around town is getting oddly warm, and that definitely can be caused by a bad fan clutch. The fan clutch is an absolute bitch, or it was for me when I did it two weeks ago; not a lot of room to work and a lot of stuff to bang your hands on.

 

Good call, I’ll go look at that.
I did think maybe the radiator is just getting old, thought about removing and having it flow tested

 

If you remove it, may as well replace! With that mileage it may start leaking soon. I look at them as almost a maintenance item on these around 150k.

 

Yeah I have seen it before at 202ish but not going 75 on flat ground, low rpm not really working that hard.

Does the fan help evacuate hot air from behind the rad at highway speed or does it contribute very little at that speed?
I’m also not sure how to test it? Seems like at 185deg it's weak and 195+ it's stronger.
Here is a video of it stopping after reaching operating temp at idle, I believe the gauge said 184.

https://youtube.com/shorts/Pqe-zmf3f4g?feature=share

 

If you happen to offroad thru tallish grass, check from underneath between a/c condensor and radiator, mine gets full of grass there after a couple offroad trips.

The radiator cap sounds suspect too, does the coolant reserve tank look normal (moving between the hot/cold marks)?

My 5.7 doesn't leave the 190-194 range regardless of ambient temps, up CO mountains or hot beaches just cruising. (I scan it with Torque). Now the transmission temps are another story, one like all of you are not happy with.

 

Yeah looks normal, when cold it’s half full, when it’s warm it’s full.

I agree I think mine used to stay below 195

 

Pulled the cap off looks in tact, tested the fan clutch a little more thoroughly and it actually seems ok, I think I assessed it at too low a temp before. Looks like it engages around 190deg

I ordered a cap, I suppose if that doesn’t work i’ll pull the radiator and have a rad shop flow test it, I also ordered a combustion gas test kit, hoping it’s not a start to a head gasket issue

 

Combustion leak test passed so I pulled the radiator and had it pressure tested, small leak in the top by the return hose.

Toyota said the factory radiator is 2-4mo out. Anyone have a good aftermarket recommendation? Or know the Denso part number for the factory radiator?

 

Check the aluminum ones
https://www.mishimoto.com/performance-aluminum-radiator-toyota-tundra-2007.html#prettyPhoto

 

Those temps are normal.

 

Another option is a lower temp Thermostat - https://www.mishimoto.com/toyota-tundra-2007-low-temp-thermostat.html

 

Well I replaced the radiator, thermostat and the coolant and cap. Now it idles about 188, haven't seen the temp go above 198 yet since then.

I guess the bad radiator was allowing air to get trapped.

 

Did you use oem from Toyota, Denso, or mishimoto for the radiator?

 

Well I ordered Denso twice since Toyota said they had no idea when they could get one. Both Denso rads came damaged badly. So I went with performace radiator,
They seemed fine and honestly the quality of the rad looked better than denso IMO