Coolant Leak - No Hot Air

[rtd111]

94 SC400 124K miles

I had noticed an odd smell in the car, in retrospect, it was leaking coolant, I believe.

A few days later, I noticed the temp needle went to 3/4 + level -- usually its barely at half.

The same morning I noticed the car was not blowing cold air even when I dialed up the temperature (it was cold outside). My wife said she saw a trail of something out of the car (was coolant).

I pop the hood. There was remnants of dried coolant all over -- some even splashed towards the engine cover and thermostat area (the area was dry there but had white spots, of evaporating coolant). The coolant reservoir was empty.

I've refilled it to see obvious leaks. There aren't any.

Poking around, I discovered the coolant pipe near the firewall is the culprit: it's got dried / caked coolant on it. There's some sort of a temp/ac sensor there I believe with intake-outtake pipes. I unclamped the one running along the firewall - it is dry. the one running below is caked and this goes into the interior vents, I deduce (blowing hot or cold air depending on A/c off or on).

Qu:

1) any suggestions on how to diagnose the problem

2) the lower vent pipe has an oddball clamp on it. With the caking around it, its hard to figure out how to remove it. Looks like a pin that I could just pull down to unclamp. Is this right? I will clean up the caking there and try again -- though its hard to reach there. I've removed the two screws that hold the "sensor".

3) Should there have been coolant in the horizontal pipe: the one that goes to the sensor? Also what's the circulation path for the coolant here? I recall in a coolant flush tutorial that this pipe is another way to empty the coolant. Does the car need to be running to have coolant in this pipe?

Thanks for your responses.

[elvisisking]

It sounds like it may be the water pump seal. If so then your looking at replaceing the water pump and the timeing belt. Good luck.

[rtd111]

It sounds like it may be the water pump seal. If so then your looking at replaceing the water pump and the timeing belt. Good luck.

Thanx for the response.

How can I confirm this? Its either the heater solenoid or what you are suggesting. I could make the smaller investment (in the solenoid) and see if it fixes it, or move on to the TB & WP... or

Where do look for the leak -- I don't see any obvious drip with the engine running, hot or cold. I noticed after my 15 miles drive home today that there was just a very small puddle in the undercarriage cover -- right under the reservoir actually.

Note that the heat works now since I topped off the coolant. But it blows hot only when I dial up to max or close to that -- at 71-72 degree setting, I got cooler, not cold air (note that I am in Seattle and did need to use the heat this morning).

Appreciate additional insights.

[elvisisking]

Your getting heat that mean that the WP is still operational. The coolant is probably leaking from the weep hole on the WP. If the seal is bad the leak is only going to get worse. Of course the longer that the car is running the better chance that you will be able to see the leak. I hope that I am wrong with my diagnosis, as I am sure that you know that this is not a cheap fix,

I am unfortunately talking from experience. My three hour drive to northern MN this past weekend took me six and a half hours. My 95 SC 400 with 146K. Started overheating about two hours into the trip. I made it to a gas station bought coolant, I made it another 25 miles and I started overheating again, I did this three more times before getting to my final destination.

[UCF3]

Are you seeing any smoke coming out of the tail pipe? White indicates a coolant leak into the engine. Also when was the last time you completed a Coolant Flush, and is your thermostat going up anymore?

I'm thinking the lack of coolant may have shut the A/C Compressor which may require servicing, and it might have been a clog that caused the leak, but this is just a though. Can you post some pics to this thread so that we can see what you're referring to?

[elvisisking]

Any luck on the coolant leak???

New WP, TB, and T-Stat. Plus labor for my 95sc 400 was $1095.00

Hope every thing turned out ok for you

[eatingupblacktop]

Any luck on the coolant leak???

New WP, TB, and T-Stat. Plus labor for my 95sc 400 was $1095.00

Hope every thing turned out ok for you

Why the throttle body? Did it need replacing?

[eatingupblacktop]

94 SC400 124K miles

Was the WP replaced at your 90k service?

[elvisisking]

Any luck on the coolant leak???

New WP, TB, and T-Stat. Plus labor for my 95sc 400 was $1095.00

Hope every thing turned out ok for you

Why the throttle body? Did it need replacing?

TB = Timing belt

[eatingupblacktop]

Any luck on the coolant leak???

New WP, TB, and T-Stat. Plus labor for my 95sc 400 was $1095.00

Hope every thing turned out ok for you

Why the throttle body? Did it need replacing?

TB = Timing belt

Of course. I was reading another forum and had throttle body on my mind and for some reason couldn't understand why anyone would change their throttle body at the same as the WP and stat. Just did not compute. Must have entered the Twilight Zone.

[rtd111]

Are you seeing any smoke coming out of the tail pipe? White indicates a coolant leak into the engine. Also when was the last time you completed a Coolant Flush, and is your thermostat going up anymore?

I'm thinking the lack of coolant may have shut the A/C Compressor which may require servicing, and it might have been a clog that caused the leak, but this is just a though. Can you post some pics to this thread so that we can see what you're referring to?

Sorry, I have been out the past few weeks & too much work.

No there is no white smoke from the tail pipe.

Here's the status. After I filled the coolant around end of May, I've not had to fill it further. There may be a slow leak - on occasion, when I open the hood, I see a small puddle on the undercarriage.

Actually, now that you mention it, the a/c has become weak though it does blow a bit of cold air. The hot air still comes on at about 76 deg (I would expect it at 71 - Seattle weather was rainy / cold couple of weeks back).

Basically, the problem remains unresolved, and it seems to be on a "slow burn".

I will post pics in the next posting -- car's not here right now. Thanx for all your responses. Expect to be more regular with replies.

[jdish]

Are you seeing any smoke coming out of the tail pipe? White indicates a coolant leak into the engine. Also when was the last time you completed a Coolant Flush, and is your thermostat going up anymore?

I'm thinking the lack of coolant may have shut the A/C Compressor which may require servicing, and it might have been a clog that caused the leak, but this is just a though. Can you post some pics to this thread so that we can see what you're referring to?

Sorry, I have been out the past few weeks & too much work.

No there is no white smoke from the tail pipe.

Here's the status. After I filled the coolant around end of May, I've not had to fill it further. There may be a slow leak - on occasion, when I open the hood, I see a small puddle on the undercarriage.

Actually, now that you mention it, the a/c has become weak though it does blow a bit of cold air. The hot air still comes on at about 76 deg (I would expect it at 71 - Seattle weather was rainy / cold couple of weeks back).

Basically, the problem remains unresolved, and it seems to be on a "slow burn".

I will post pics in the next posting -- car's not here right now. Thanx for all your responses. Expect to be more regular with replies.

I just had the same problem in my SC400, It ended up blowing steam when I couldn't find the leak, found that it was the hose by the firewall at the back of the engine. It was tough to get to but it fixed the problem. I believe that it runs to the heater core which would explain why your not getting heat. I had tried to run the defrost to keep it cool when it was overheating but no heat was coming out since the path was open and the coolant couldn't flow. You really can't see the bottom of the hose unless your right over it so it is hard to detect, I Strongly suggest just replacing it as it is one that would get left since it is hard to get to. Hope this is helpful.

[rtd111]

I just had the same problem in my SC400, It ended up blowing steam when I couldn't find the leak, found that it was the hose by the firewall at the back of the engine. It was tough to get to but it fixed the problem. I believe that it runs to the heater core which would explain why your not getting heat. I had tried to run the defrost to keep it cool when it was overheating but no heat was coming out since the path was open and the coolant couldn't flow. You really can't see the bottom of the hose unless your right over it so it is hard to detect, I Strongly suggest just replacing it as it is one that would get left since it is hard to get to. Hope this is helpful.

Coming back online after a few months: the SC400 with the problem I stated has been sitting idle for the last 4 months. I had my brother's car but that is going away so I need to fix this problem in the next 3-4 weeks.

Answering a prev qu: the timing belt and water pump were replace about 6-7 years ago, at 75K miles. I bought the car used at the time and it had the 90K service done by the Lexus dealer. I have all the records.

Also, I tested the thermostat yday: the valve opens around the 80-90 degree-C temp.

Per the quote above, what tube is this? Can you point to it in the manual or send a pic?

In reading similar threads on the LS400 forum, one diagnostic is an air pocket in the system. I had drained and refilled coolant about 2 years ago now (Dec 06) and this problem started about 14 months into that (Mar-Apr 08). So could the air pocket theory apply? Note that its been about 6-7 months since this problem first surfaced.

So, any new learnings in this group that might help? Thanks in advance.

[rtd111]

Any thoughts or suggestions, folks?

Given there is a problem with coolant leak only when running (escaping when hot and under pressure), and its not the thermostat, perhaps there are a several more directed questions here for various suspects:

- How do I test there is no leak in the radiator?

- How to test the heater core and the sensor there to make sure coolant path is not "clogged"

- how to check for air in the system

- how to check the water pump

Looks like something is causing very high pressure in the system and the coolant is being forced from the weakest points (???)

Thanks.