Temp goes to HOT 5 minutes after shutoff

[thechief]

[font=arial] The coolant temperature of my 1995 Ranger 3.0 L w/ 100,000 miles has always run right in the middle of the gauge at operating temperature. If after the engine is up to temperature, I stop for 5 minutes (like to get gas), when I restart the engine, the temperature is at HOT, and stays there for about 1 minute, then suddenly drops back to the middle of the gauge. It has done this a couple of times a year for a few years, but in the past few months, it has been nearly every time I stop for 5 minutes. I have flushed and changed the coolant, changed the thermostat and the temperature sensor, and none of these things have had any effect on this problem. There are no other symptoms, coolant doesn't push out into the reservoir when this happens. I pulled the wire from the sensor and measured resistance, and it drops when the temperature increases, indicating that the increase is real, nothing to do with the gauge or associated circuitry. Anyone have any idea what may be causing this?

[rdavid8221]

Originally Posted by thechief

[font=arial] The coolant temperature of my 1995 Ranger 3.0 L w/ 100,000 miles has always run right in the middle of the gauge at operating temperature. If after the engine is up to temperature, I stop for 5 minutes (like to get gas), when I restart the engine, the temperature is at HOT, and stays there for about 1 minute, then suddenly drops back to the middle of the gauge. It has done this a couple of times a year for a few years, but in the past few months, it has been nearly every time I stop for 5 minutes. I have flushed and changed the coolant, changed the thermostat and the temperature sensor, and none of these things have had any effect on this problem. There are no other symptoms, coolant doesn't push out into the reservoir when this happens. I pulled the wire from the sensor and measured resistance, and it drops when the temperature increases, indicating that the increase is real, nothing to do with the gauge or associated circuitry. Anyone have any idea what may be causing this?

It is normal for the temp to rise when the vehicle is just shut off. This is do to the fact the coolant is not circulating. This is normal.

[thechief]

Originally Posted by rdavid8221

It is normal for the temp to rise when the vehicle is just shut off. This is do to the fact the coolant is not circulating. This is normal.

Thanks for the reply. I understand that, due to the heat still in the block, but for it to stay all the way at Hot for a minute (literally), then suddenly, not gradually, jump down to mid-scale on the gauge as if there was no coolant flow and it suddenly started. Also the fact that it only did this a couple times a year until just recently indicates that something was very intermittent, and now has permanently broke. Is it possible that the water pump vane is spinning on the shaft for a period of time?

[rdavid8221]

Originally Posted by thechief

Thanks for the reply. I understand that, due to the heat still in the block, but for it to stay all the way at Hot for a minute (literally), then suddenly, not gradually, jump down to mid-scale on the gauge as if there was no coolant flow and it suddenly started. Also the fact that it only did this a couple times a year until just recently indicates that something was very intermittent, and now has permanently broke. Is it possible that the water pump vane is spinning on the shaft for a period of time?

It could be your water pump; but I Don't think so. I had a 1986 ranger and now I have a 1999 and with both trucks the gauges are wacky. On the 99 the oil gauge won't go up for about a minute when I first start the truck. On a couple of occasions with both vehicles while driving, all of the gauges would just look like they were hit by lightning and be all over the place. It is worth getting checked out for your own sake and peace of mind. Do what you think is right so you can be comfortable.

[Mark E M]

Outside shot.. Check the battery neg. connection, from battery to the engine, if loose I've heard all sorts of problems... from this. Just an outside shot though. Later, Mark.