Heat Only When Rpm Above 900

[sprintuser]

Greetings, I have a 1997 LS with 154000. It is starting to get cold in Wisconsin and I lately noticed that when idling, the car does not produce heat...................only when the RPMs are increased above 900 does heat start coming from the vents, otherwise, its cold/ambient temperature air.

I called a local parts store and the gentleman told me it must be the temperature control valve getting stuck. THe higher RPMs are causing more pressure from the water pump and thus opening the valve.

I tried checking the coolant level last night but it was hot and starting steaming out, so I closed it right away.

Questions for your respected input:

1. Do you folks agree with the diagnosis?

2. If the diagnosis is true, has anyone changed/does anyone have the directions to change the temperature control valve?

3. Should I change the coolant? Also, the timing belt was changed at 92000 miles, not sure if the water pump was. I don;t have any leaks on the garage floor, will this problem have an impact on my water pump?

Thanks in advance!

[python]

sounds like u r low on coolant, check it in the morning before u start it up, most guys at the parts places dont know too much, some do but in general they are just order takers...i would call a shop before i would take advice from a parts guy,or just have it looked at if ur coolant is at the level it should be

[sprintuser]

THanks for the input. I am thinking of doing a coolant flush. Has anyone documented on how to do that on a 1997 LS?

[thisisludicrous]

This is one of my precious few areas of expertise on our cars. Same thing happened to me, my mechanic told me I needed a new coolant tank cap. Sounded too easy, but I let him top off the tank and put on a new cap - and it worked.

Don't let me talk you out of the coolant flush, but I wouldn't try to overthink the problem until you try this easy fix for less than $15.

There are a few threads on this in the archives, if I was my proficient at searching and linking, I'd provide the link. At the risk of sounding immodest, try using the search for "thisisludicrous," and that should bring up my thread on this topic, at least.

Best of luck.

[Alexander the o.k.]

I would agree in principal with the heater control valve being stuck in the semi open position. You may be able to test this. Just look for a small valve high up on the left side firewall (on a '92 anyway) with a hose attached at the 6 o'clock position, and a cable (coming from the firewall) at the 9 o'clock position. This is your heater control valve. When the engine is hot, put temp on 85 *, then pull on the cable to ( help me here guys, either all the out, or push all the way in) to open it to allow the hot coolant to flow into the heater core. If it is stuck, say halfway, then that's your problem. Replace it.

Then do the flush and put in Toyota coolant only.

[Top Jimmy]

Hats off to you guys. Just did a quick coolant level check and found it lacking. Brought it up to proper level and curred the "no heat at idle" blues.

Now, in the process of this fix, I discovered error codes 14 and 15 when running the AC diagnostic test. I know that 14 is an open or short in water temperature sensor (though I don't know the effects nor fix). However, I have been unable to determine from any source what error code 15 means.

Thanks!

-Jimmy

[Marklouis]

I just experienced this issue in My 95, and topping off the radiator fluid has corrected the problem - thanks Python!

[sprintuser]

Thanks for all the helpful input folk. I have not logged in fora while cause I slammed my LS at 40MPH into a pavement (slipped on black ice and hit the right side on the pavement). Have been dealing with that issue.

At the time the suspension was being worked on, I went ahead and drained the coolant (from all three points; the radiator plug and the two engine bolck drain plugs under the car). When we re-filled the engine block, there were a few minutes of concern. The temp went almost red (turend the engine off before it could get to red), but the system burped, filled up more coolant and everything was well........................except the 'no heat at idling' issue.

So, I will try and find the temp control valve and see if it the culprit (thanks Alexander!). I will keep you guys posted.

[astar617]

I also will look for this... having the same problem on my 96 LS400 and coolant level was quite full, so heater control valve check will be next... stay tuned...

[ck42]

I also will look for this... having the same problem on my 96 LS400 and coolant level was quite full, so heater control valve check will be next... stay tuned...

Just had this same problem about 2 weeks ago. I also was having a slow coolant leak somewhere mysterious...so it went in the Indy for both issues.

Turned out both problems had the same cause. it was the heater control valve. Malfunctioning...AND it was leaking. Something like $80 for the valve and .5hr labor to install. All is well again.

With mine though, it took revving the engine to about 2700RPM before the heat would suddenly start flowing. It was really weird how it went from ambient to instantly hot as soon as I hit the magic RPM point.

(Coolant level was not low when it was behaving like this...despite there being a slow leak - I was keeping it topped off)