Hey guys, I have owned my S for 7 years, just today I noticed that when I come to a stop and the car is at idle, the heat gets colder, then when I rev the motor it gets hot again. I wanted to get some ideas as to what this is about since its never done this before. Thanks much

 

sounds coolant related. have you recently done a flush on the system?

better safe than sorry to check the coolant level when you can. with the car cool remove the rad cap and see how high the level is in the radiator. then get back to us

 

^^

what he said. also what climate are you driving in. do you still have your front inner fender liners?

 

Has to be related to coolant as stated above. I would imagine that you are low on coolant. If this is the case, refill the radiator and overflow tank and loosen the bleeder valve on the block first. This may take a little time and a few cycles of the thermostat kicking on and the fans running. Once there is a steady stream of coolant running out of the bleeder on the block, then tighten it back up. Next, do the same for the bleed nipple on the heater core bypass hard line that runs across the firewall - it should be the upper line that has a nipple that runs almost strait up off of the line and is capped off by a rubber cap and clamp. While you do the heater core, make sure the HVAC controls are set to full hot and you have the fan on enough to be able to feel it with your hand. It may take a few cycles on this one just like the block bleeder valve did but it should eventually get hot and the air will be bled from the heater core. Once you are done with all of this, refill the radiator and overflow tank and check on it after you run the car for the next few days making sure it is all topped off as the motor will bleed off any other air bubbles and pull coolant back into the system from the overflow tank.

 

Hey thanks for the responses and info guys I really appreciate it. I'm a bit confused though since I have not touched the coolant system. The radiator is full, the reservoir is half full where it should be. The car stays at the appropriate 3bar temp, no engine overheating issues, everything normal there. The heat just now gets luke warm when at idle, and back to hot when I drive or bring the motor revs up. Its never done this until now, its always maintained the same heat from idle up. So what has changed?

Chew on that one for a wile guys

I hope its nothing to worry about, that's what matters to me.

 

If your coolant level is ok I would check next the heater valve. It is located on the firewall to the left of the valve cover where the 2 heater core lines run into the firewall. Have another person change the temperature from hot to cold repeatedly and see if the valve is opening all the way.

 

It sounds more like a blocked heater core. I just changed mine out after a cold car for
Most of the winter. I cut my old core open and found that this core has the tiniest passages I have ever seen in a heater core. I have about 140 ,000 miles and have flushed the coolant every spring since I bought it about 5 years and 50,000 miles ago. So, bite the bullet and pull your dash. Oh, I had checked the flow and it was flowing just fine. Just flowing through about 3 of the cores. Send me your email address and I'll send you some pics of my old core. I am now flushing my new used core on a closed loop for several days to make sure it's clean. I tried to flush the original core but only with the engines water pump. So it was only flushing for a little while compared to the hours this one is receiving. It had better heating already so I am anxious to see how this works. I can let it backflow for as long as I want to. I can send you pics of how I have setup the incar bench backflow. Good luck!

 

It was the radiator cap gasket. Just picked up a new cap from Honda for $12, Problem fixed