cb

Any comments or suggestions would be much appreciated.

The story:

Every time I turn my truck on and get it up to highway speed, from cold, the temperature gauge rises, and continues to rise until just below the red (overheating zone), and then the needle quickly drops down to a normal engine temperature and stays there for the entire trip, no random fluctuations in the gauge.
Further, it is not burning coolant, but after driven, the coolant level in the rad goes down and up in the reservoir. Let sit for two days, the coolant level goes back to a full rad and normal reservoir.

The water pump was replaced in November, so I inclined to suspect it.

toytech76

what about your tstat? A faulty tstat or a headgasket issue can cause that

abecedarian

when was the thermostat last replaced?
I'd almost be willing to rule out the headgasket since you say the temp stays constant after that initial 'excess reading'.

LIYOTA

i have the same problem. replaced the water pump and thermostat checked the HG. Happens less frequently now but still with some regularity. Im almost thinking its my temperature guage grounding out or something.

Noltz

I'd wager a faulty t-stat. Sounds like it's sticking. The gauge can be verified with a rheostat or use a laser thermometer while it warms up.

norcalsvx

probably a t-stat this is from 4crawler


Thermostat:

After everybody looked at me like I was crazy for saying that it ran hotter with the heat on, I went to the dealership and bought t-stat part # 90916-03070. This did the trick. What happens on the 22R and 22RE engine, when the coolant goes through the heater core it gets cooled off enough that when it gets dumped back in on top of the t-stat it shuts it. Therefore the temperature in the engine continues to go up. The t-stat that I have mentioned has two valves in it, one at the regular temp. and one smaller on at a cooler temp. If the cool water shuts the big one, the smaller one stays open. The overshooting/spiking temperature gauge may aslo appear independent of heater operation.

All this may happen because of some flow instability in the cooling system or the lack of a by-pass hose, which on other systems, keeps hot coolant running on the t-stat. On the subject of the overheating thread, an engine can run hotter with no t-stat. But it would probably be a system configured differently than the 22re. Mine runs cold when the t-stat is removed. Just a minor change in components can trigger this problem. In my case, I had a rebuilt engine installed. No problems with the original engine, but the new one (block and head - wame water pump, t-stat, radiator, etc.) was enough to trigget the temperature gauge overshoot.

Another advantage of the 2-stage thermostat is that the thermal "inertia" of a thermostat is greatly affected by the mass of the temperature sensing element (a.k.a. slug) on the thermostat. The normal single-stage t-stat has one big valve with a large spring and a large slug to force the spring open. The 2-stage t-stat, on the other hand, has a tiny valve and a medium sized valve, with tiny and medium sized springs and slugs. This lets the smaller t-stat valve react very fast to engine temperature changes and the medium sized valve, although a bit slower, still operates faster that the one large valve.

A lower-cost version of this can be done by drilling one or more small holes around the edge of the single state t-stat to allow some coolant to flow all the time. This functions like the normal bypass hose on other engine designs.

On the subject of thermostats (or turd-mo-stats for Toy4x4 old-timers:-), I once tried one of those "fail safe" thermostats. A normal t-stat has a spring that holds the valve closed and the slug forces the valve open in response to coolant temperature. The slug has a sealed chamber with a temperature sensitive medium in it that expands when heated. The typical t-stat failure mode is that the chamber leaks or swells, preventing the t-stat from opening. The fail safe thermostat has a catch that is engaged when the t-stat valve opens fully and then the valve is held open. I guess the idea is that if the engine ever does begin to overheat, the t-stat locks open and prevents further damage. Well anyway, I had installed one once, and it worked fine. One day, I lost the silicone oil out of my fan clutch (didn't notice this until later when I popped the hood and saw the results) on a hot (100F) day. I recall seeing a slight temp rise once, but nothing too bad. Some weeks later, on a cool night, I turned on the heater and got almost no heat. This is when I popped the hood, saw the oil sprayed all over and put two and two together. Pulled the t-stat out and sure enough, it was latched open, so I guess it did its job. However, I now had to replace the t-stat, since once it locks open, it can't be reused. But I guess this also shows the engine runs cooler with at least a wide open t-stat in it.