Running cooler than normal

[manoa matt]

I've bee driving it daily for a few months now and everything has been normal up untill yesterday. Typically my water temp gauge reads between the 1 and 0 of the 190 mark, usually hovers over the 9. It never really ran under the 1 and never past the 0. I've never had an overheat problem either. The water pump, thermostat, hoses, and radiator are virtually new. The coolant is good and there is no air in the system.

The rad. fan switch, coolant temp gauge sender, and overheat switch/sender are the only things that are not new or age/condition unknown. Lately the temp has been holding steady just before the 1 of the 190. The fan still comes on when it should. The lower rad hose is hot, but I'm not sure I could tell the difference between 180 and 190 with my hand.

My theories are: 1. the thermostat is not fully opening, 2. the fan is coming on too often, 3. The temp gauge sender is going bad.

When the fan switch goes bad it usually stops the fan from working. What happens to the temp gauge sender?

An intestering side note: I've done the brown wire fix months ago but never did the headlight relay trick. When I turn on my headlights, the engine rpms stay the same but my tachometer drops a few hundred rpms. I think the headlights are just sucking power from everything else. The wierd thing is that the water temp gauge and gas gauge will read higher when the lights are turned on.

Why am I suddenly running a few deg cooler? I will pull the thermostat and rad fan switch and test their operating temps in a pot of boiling water, what else could it be?

[Danno]

My theories are: 1. the thermostat is not fully opening, 2. the fan is coming on too often, 3. The temp gauge sender is going bad....
Why am I suddenly running a few deg cooler? I will pull the thermostat and rad fan switch and test their operating temps in a pot of boiling water, what else could it be?

well, I can tell you right now, it isn't "1. the thermostat is not fully opening," that usually makes it hot, not cool. But the reverse could be true, I guess. Not fully closing.

[So Cal Mark]

since the gauge reading changes with electrical load, you most likely have a bad ground from the inst. cluster

[manoa matt]

I understand why the gauges change when I turn on the lights, that has happened for a while now.

What I don't understand is why I'm reading a few degrese cooler all of the sudden. This is in the day time with no accessories or lights on. Could it be the water temp thermo switch, or the water temp gauge resistor?

[pope]

I dont see this as a significant problem. Just watch it and observe. It sounds like things are just breaking themselves in and working in conjunction with other parts. Sounds more like an engine break-in period than anything. But...keep watching it.

If it was a 25 degree change, thats one thing...but this is not that.

[racydave]

The ground pod for the dash is to the right of the ign switch. My fan does not run often in the summer. Id bet its the new thermostat! One of thoes laser temp guns would be fun to play with...

[manoa matt]

Well, like all my other wierd problems, two things got mixed up.

I remember now my machineist switching the temp sensor and the temp overheat switch when I had my head redone.
The temp overheat switch has a larger base and when screwed into the forward hole in the head the base of the sensor interferes with a bump in the head casting. When the sensors are switched there is no interference. He thought the previous owner got them mixed up so he switched them. I should have double checked the wiring so its sort of my fault.

After correctly hooking up the sensors, the temp reading at the gauge is higher but it still reads a bit low. Now the needle hovers over the 9 instead of before the 1.

Here are some readings I took with a infrared laser thermometer: $ 20 at radio shack

Ambient: 78F
Temp at rad inlet: 188F
Temp at rad outlet: 165F
Metal temp of head near sensors: 190

I am going to pull and test the external thermostat this weekend to make sure it is fully closing to eliminate that possibility. I will also correctly ground my instrument cluster so there is no variation when the lights are turned on. I think I'll add the sensors on the next vendor order to see if I can get a more accurate temp reading and for piece of mind.

I hope it is not the thermostat, its less than one year old and $40 for a new one is not cheap. I have the correct water outlet casting to switch to the in-head thermostat. I can get the 2 hoses and the in-head thermostat for about half of the price of a new external type thermostat. I hate to keep installing 40 thermostats that last less than one year. I wish our vendors would offer a 1 year warranty on some of the parts, limited lifetime on others.

I've heard that flow with the in-head type is not as good causing variations in water temp in the head from front to back. I did eliminate the heater core and hooked up the heater tube to the head so flow to the back should be a little better. Consequently when I removed the heater core and connected the heater tube to the back of the head the car ran a few deg cooler.

Any comments regarding in-head thermostats??

Matt

[So Cal Mark]

the bolts that hold the water outlet to the head are very susceptible to stripping. As for warranties, when we buy parts from Europe, they come with no warranty at all. Any warranty offered to the customer is on our dime and raises the price they sell for. When you complain to a supplier, your option is to buy somewhere else.

As an aside, most of the thermostats I've seen that supposedly had failed worked just fine when tested in hot water. The theory of the thermostat is to maintain a constant temperature in the engine, so if yours is running 190 all of the time I'd say you have an ideal situation