Motor Vehicle Maintenance & Repair Asked on January 17, 2021
I have a 1997 Caravan (base model) and normally on my drive to work and my highway drives in rush-hour, the engine warms up just fine.
I took a road trip for work, about an hour and fifteen minutes of driving at basically 60-80mph the whole way. The engine never warmed up. In fact it went from being warmed up (about halfway up the gauge) to just barely above the Cold marker.
My blower only works on high, (a problem for another day) so turning on the heat for that chilly drive made the problem even worse (lost like a bar and a half of engine temp for running the heater at 75% temp, full blower, for maybe 10-15 minutes.) I turned off the heat for the last 30-45 minutes of the drive and it still never returned to normal temperature.
It’s the Mitsubishi 3.0L V6, which I believe is a cast-iron block, if that helps.
It’s also a 3-spd, so the engine works pretty hard to maintain highway speeds above 60, it should be producing plenty of heat. What’s the best way to go about solving this problem?
(For comparison sake, in stop and go traffic, on my way into work, it takes about 20 minutes for that engine to warm up, not using the heater.)
It sounds like the engine thermostat has failed in an open state. The thermostat regulates the flow of coolant between the radiator and the engine. When the engine needs more heat, it closes and cuts-off flow through the radiator. When the engine needs less heat, it opens and allows flow to the radiator. With the thermostat stuck open, the flow through the radiator is constant and so your engine will have a hard time keeping it's heat.
This sort of problem can happen anytime, but it's not until the weather starts cooling that it gets noticed. Colder outside air means more cooling from the radiator.
As your your other question, "could any serious damage have been done with the engine below operating temp at highway speeds..." The answer is probably not. You may have lost some fuel economy, but cooling an engine too much shouldn't be too much of a problem. The other extreme, having too much heat, is where engines start to have big problems.
In either case, a replacement thermostat is typically very cheap, usually < $25. Changing it depends on how easy it is to get to and how comfortable you are with draining some radiator fluid and refilling it.
Correct answer by jwernerny on January 17, 2021
In case replacing the thermostat doesn't work, it might just be a broken Coolant Temperature Sensor, which is what sends the info to the gauge.
Answered by riotburn on January 17, 2021
Though I defer to the two previous explanations a third one is also possible because I've experienced this in one of my own past vehicles. I had a small mid-engined sports car that had the radiator in the front and long pipes that carried the to and from coolant round-trip between the front radiator and the engine in the back of the car and during winters regardless of thermostat if the system was too low on coolant the engine block temp sensor would not get enough hot water contact to ever get the temp gauge off the cold market for the entire winter trip, most noticeable around & below freezing 32 degrees F. Even though the car never overheated it definitely wouldn't get the cabin heater hot until I added more coolant to the car. Put more coolant into the system and the temp would pick up and the cabin heater would heat. Ironically the cooling system was so big for such a small engine that even with the a/c on sitting in Dallas, Tx traffic during the hottest of summers in August in Texas that car never overheated as long as coolant was at least 2/3 of full thus adequate.
Answered by Pal Adino on January 17, 2021
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