Chasing an Issue.

[CruiserQuizzo]

I live on the Lower Texas Gulf Coast in Corpus Christi. I have had my 100-series for about five years now. I purchased it used with 187,000 miles on it from a family that used it mainly for highway travel between Corpus Christi and Houston, Texas. I do my best to perform routine and preventive maintenance and keep it in good driving condition for the harsh conditions of the Padre Island National Seashore (55 miles of raw beach) where we do lots of catch-tag-photo-release shark fishing.

My cruiser currently has 235,000 miles, runs great, no leaks of any kind, and it has not always had this issue. The issue I am chasing has to do with highway driving and never during city driving. My temperature gauge usually reads right in the halfway point between hot and cold while driving. However recently I have noticed that the temp creeps up at speeds any higher than 75 mph (about 2600 RPM). It is my understanding and experience that the faster you move, more air moves, engine runs cooler. That is not the case here. It is not overheating however, and when I slow back down it comes down to the normal halfway mark. I don' t drive fast, the speed limits are typically 75 mph on highways here. My fear is that the temp rising is going to cause some other part to fail as it goes under more pressure.

I perform regular oil changes (Mobil1-HM), In the last year I've replaced the radiator and hoses, coil packs and plugs (Denso, NGK), In the last few years I have replaced the water pump, timing belt, thermostat, brake booster (Toyota), Aternator (Mean Green), and Battery (NorthStar).

I am struggling with this one and I do not know what to check next. I have not looked toward my exhaust system yet (possibly catalytic converter getting clogged).... Has anyone ever had this or a similar issue? I need some cruiser advice, please!

 

[2001LC]

A lean fuel condition will result in high cylinder head temps.

Using 44K on a regular basis is beneficial, keeping fuel & combustion system clean.

Fuel pump weakening, fuel filter restriction, fuel pressure regulator weak, fuel injector need servicing. These can all reduce fuel flow resulting in lean condition, which may not throw code.

 

[Spike555]

Yes at high speeds you get faster air flow, you do not get more air flow, you get faster air flow, BUT the engine is working harder so it runs hotter.
Simplest and most cost effective solution, slow down.
You say 75 isn't fast, to me that is.
The speed LIMIT is not the required speed of travel, it is the maximum speed of travel allowed by law.

And yes, I have had this issue, on every single big diesel truck I have ever driven, the harder you work the engine the hotter it runs.
That could mean climbing a long grade while empty or dead flat as a pancake while fully loaded at full throttle.
If the cooling system was not working properly, you'd be running hot at low speeds too, but your problem is solely based on engine load.

 

[Spike555]

To add to your issue, running the tires at a higher psi will descrese rolling resistance.
Also fresh gear oil, some gear oils get thicker as they wear out, which increases gear drag which makes the engine work harder.
Those are two simple do this weekend things you can do to possible help decrease engine temps at higher engine loads.

 

[Leandro]

Have you checked your fan clutch?

 

[SmoothLC]

What's your engine temp? Got a ScanGuage/DashCommand/Torque app?