DCYota

'88 Pickup, 22RE.

Here's what's been done as far as the cooling system is concerned.

Water Pump is new
Fan Clutch is new
Radiator is new (3.0 V6 Rad. was swapped in by the previous owner)
All hoses (upper, lower, etc...) are new
New OEM Toyota Rad. Cap (replaced by me last week)
New Dual Stage Toyota t-stat (replaced by me last week...works by testing it on the stove before install..opens as it should)
Coolant flush and fill recently performed (about 1 week ago).
Coolant level in rad. is fine, as well as the overflow tank.

When I start it up and let it idle, the temp gauge reads normal...never above half..usually just below halfway. City driving is normal at times. Sometimes it stays below half...sometimes it creeps up past the halfway mark, but then settles at about half on the gauge. Through all of this, the heat works just fine...blows nice and hot.

Highway driving is when it gets "interesting". The needle goes up 3/4 of the way to the top, and sometimes more . Never in the red, but sometimes right below the top white line. The funny thing is, when I stop driving it at that point and open the hood, the under hood temps seem normal. I can put my hand on just about anything under there and not get burned. The rad. cap is hot as expected, and the upper hose is hot that comes from the t-stat to the radiator. But it's nothing like what you get when you open the hood of a truck that has obviously over heated.
The radiator itself is also hot as expected, but not scorching hot. No steam escaping from the cap, and no bubbling/boiling going on. The truck runs perfect. No loss of power, no idle issues, no stalling, or anything like that. It runs really well. No white smoke or discoloration at all from the exhaust, so I know it's not a head gasket. Gas mileage is great (about 17mpg consistently) There are no coolant leaks, nothing dripping on the ground or coating any part of the engine.

So what gives? I've ordered a new temperature sensor and a temperature sender today, and that should be in this coming week just so I can rule out the possibility of a faulty gauge and bad readings. After I put in the dual stage t-stat I burped the system with the heat on full, rad. cap off, and let it idle for about 20-30 minutes squeezing the upper hose and getting the air out. All of this was while the truck was parked on a steep incline to get the rad. cap as the highest point in the system.

The one thing I did notice is that while doing the radiator burp, I looked into the top filler neck at the coolant, and it doesn't seem to be flowing at all. Isn't it supposed to be moving from left to right (towards the right side of the radiator)? Could it be that this "new" radiator is clogged by something, or defective from the start? Tomorrow I had planned to take off the lower rad. hose to drain out the coolant, and stick a garden hose in the top of the rad. to see what kind of flow I'm getting.

Anyways, it's driving me nuts. The sender and sensor are the last two things I can possibly order at this point as far as ruling things out that I "think" might be wrong (such as the faulty gauge theory).

Any input or thoughts/recommendations would be greatly appreciated. I've searched and found tons of threads and have spent the last few nights reading a lot of them pertaining to the same or similar issues...but a lot of them seem to have different endings or conclusions, and some just kind of dead end completely with no resolution.

DCYota

...just thought of something else to ask...it may be a long shot but;

I installed an ARB bumper a couple of weeks ago...it doesn't have a winch in it at the moment, but I did mount my license plate over the hole that the fairlead would normally mount to. Does anyone think that this is enough blockage to keep air from moving through the radiator causing this high temp issue?

It may be silly, but I thought since I was trying to rule everything out, I may as well include that as well. Here's a pic of what I'm talking about with the license plate location:



I can remove the plate tomorrow and take it for another drive to see if that helps..but I really don't think that's enough blockage to cause that much of a temp increase...but maybe I'm wrong. Crazier things have happened

87toy.

if its only doing it at highway speed and not streets its getting plenty of air. If it wasent getting enough air it would do it on the streets in stop n go.

at higher speed it makes more heat, that little movement in your temp gauge could only be a 20-30 degree difference.

myyota

I had an 85 4x4 truck that did the same thing, it also has new hoses, thermostat and radiator, it turned out to be a bad temperature gauge sending unit.

DCYota

OK, cool. Thanks for that info so far. I really am hoping the sensor and/or sender replacement this coming week fixes the issue. I'll still do some probing like flushing the radiator to make sure it's not blocked or restricted in any way just so I can rule that out.

Thanks again...I'll keep this updated once I get the sender and sensor in, and go from there.