'99 Grand Caravan Heating Up

My '99 Dodge Grand Caravan is heating up. The van has 103K and has a 3.3 engine. The temp gauge has always run about half way up the gauge. Now going down the highway, the gauge almost hits the HOT mark. The weird things is when I get back into town driving, the temp gauge goes back down.
The radiator is not blocked and both fans are running. Seems like the fans always run. Do I have a head gasket going? Have noticed a light knock on startup sometimes. Could a bad head gasket cause the knock sometimes? Do you think I have a rod knocking? The oil always looks good and the level never changes.

When you are at speed, the cooling system is working at it's peak capacity trying to maintain cooler temperatures under load. As you come into town the demand on the cooling system declines. If coolant flow is resistricted, the temperature will rise above the normal range. A restriction could be a weak pump, partially clogged radiator, partially closed thermostat, or a collapsed hose. Could even be as simple as old/weak coolant or a slipping surpentine drive belt.

If you haven't in the past two years, I would drain and flush the system and change the thermostat at a minimum. If the hoses are 4 or more years old, consider changing them.

Yes, a leaking head gasket can create a knock. Coolant leaks past the gasket thinning and decreasing the lubricating capacity of the oil, allowing parts to wear faster. That said, if you aren't seeing water vapor coming out the tailpipe and/or notice a decreased acceleration or missing, you're probably ok. Another sign is oil in the coolant or visa versa. You likely won't see it on the dipstick but, if you drain the oil it will appear a lighter brown and may have whitish swirls in it if contaminated by coolant. Coolant will have tiny black dots or a heavy rainbow appearance on the surface. A compression check can reveal a bad gasket.

Thank you for the reply. I just replace the water pump about 4 months ago.
Replace the thermostat last night. Will test again today. I changed the oil yesterday and did not notice anything unusual in the oil. Did notice water vapor out the tail pipe. Doesn't look white. Will do a compression test and repost.

Monte.

Have not had time to do a compression test.
Seems like the thermostat swap fixed the problem. The van is running cooler than it ever has. Think the thermostat was going bad for a long time and the fans were keeping her cool. Wonder if the fans shut off going down the highway? If they do, that would explain why the van was heating up down the highway.

Any way, my fans are not constatly running and I'm back on the road.

Thank you automotiveforums!

Monte Heeren

Happy to hear all is well. Thanks for posting the fix.