Wierd Overheating Problem - Sc400, '92

[djhillssc]

My SC400 was in the shop twice this year - once back in January for a new power steering pump, and then just this last week for some routine maintenance (alignment, etc). While it was in the shop this last week, the mechanic said he noticed a small coolant leak coming from around the thermostat housing. Fine, told him to replace the thermostat.

Thursday afternoon, I get the car back. It overheats within 10 miles, on the freeway. They tow it back in to check it out.

Friday afternoon, they call me and tell me no worries they got it fixed. I pick it up. It overheats within 10 miles. They tow it back in.

Saturday morning they tell me it was a faulty new thermostat - no worries, they replaced it free of charge. It overheats again within 10 miles.

Beyond frustrating!

Here's what I know:

1. It only seems to happen when the car is under load - ie, freeway back to my house is all up hill (not steep, but it is up), it's 110 degrees outside and I have the A/C on.

2. I have not had it overheat even with fairly extensive driving on surface streets (40 mph) - though it doesn't really seem to cool down to normal on the surface streets if it's overheated on the freeway and I exit.

3. It has a new thermostat.

4. The coolant level is fine, and it does not appear to be leaking coolant (unless it overheats, then it comes out of the overflow tube on the coolant reservior).

5. The hydraulic cooling fan is coming on properly, and "speeds up" to a blistering wind when the car heats up.

6. If I turn on the *heat* full blast, the engine cools back to normal operating temp *very* quickly. (Only tried this at idle though, not while on the freeway, will try if it seems important).

Anyone have any idea why this his happening? Anything I can point to to troubleshoot it further myself? At this point the shop that was working on it wants nothing more to do with it (I think they're in over their head and afraid I'm going to pin the problem on them).

I appreciate any advice anyone can give!

Thanks,

Dan

[dcfish]

My SC400 was in the shop twice this year - once back in January for a new power steering pump, and then just this last week for some routine maintenance (alignment, etc). While it was in the shop this last week, the mechanic said he noticed a small coolant leak coming from around the thermostat housing. Fine, told him to replace the thermostat.

Thursday afternoon, I get the car back. It overheats within 10 miles, on the freeway. They tow it back in to check it out.

Friday afternoon, they call me and tell me no worries they got it fixed. I pick it up. It overheats within 10 miles. They tow it back in.

Saturday morning they tell me it was a faulty new thermostat - no worries, they replaced it free of charge. It overheats again within 10 miles.

Beyond frustrating!

Here's what I know:

1. It only seems to happen when the car is under load - ie, freeway back to my house is all up hill (not steep, but it is up), it's 110 degrees outside and I have the A/C on.

2. I have not had it overheat even with fairly extensive driving on surface streets (40 mph) - though it doesn't really seem to cool down to normal on the surface streets if it's overheated on the freeway and I exit.

3. It has a new thermostat.

4. The coolant level is fine, and it does not appear to be leaking coolant (unless it overheats, then it comes out of the overflow tube on the coolant reservior).

5. The hydraulic cooling fan is coming on properly, and "speeds up" to a blistering wind when the car heats up.

6. If I turn on the *heat* full blast, the engine cools back to normal operating temp *very* quickly. (Only tried this at idle though, not while on the freeway, will try if it seems important).

Anyone have any idea why this his happening? Anything I can point to to troubleshoot it further myself? At this point the shop that was working on it wants nothing more to do with it (I think they're in over their head and afraid I'm going to pin the problem on them).

I appreciate any advice anyone can give!

Thanks,

Dan

The radiator needs to be flushed and/or replaced. Common on the ES models and not surprised on the SC model.

[djhillssc]

The radiator needs to be flushed and/or replaced. Common on the ES models and not surprised on the SC model.

Thanks for taking a second to reply - is there any way to test the radiator specifically? Can you give me some insight into the logic as to why it would only affect the car when I'm driving at freeway speeds (70 mph)?

Just don't want to shell out more money for that only to find out it's not the problem either...spent way too much already!

This forum is awesome - thanks in advance for anyone who takes a minute to respond!

D

[dcfish]

The radiator needs to be flushed and/or replaced. Common on the ES models and not surprised on the SC model.

Thanks for taking a second to reply - is there any way to test the radiator specifically? Can you give me some insight into the logic as to why it would only affect the car when I'm driving at freeway speeds (70 mph)?

Just don't want to shell out more money for that only to find out it's not the problem either...spent way too much already!

This forum is awesome - thanks in advance for anyone who takes a minute to respond!

D

It's not circulating the coolant , It is clogged. Back flush it and see what comes out.

[mehullica]

Possible they didn't bleed out the air from the system. There's a 17mm bolt/plug on the top thermostat housing. It's in front of the "L" on the intake manifold and the small black plastic plug wire cover. That's where the coolant should be filled to purge out any major air pockets. Then the overflow bottle will purge out minor air pockets with the cap off and engine running.

[djhillssc]

Possible they didn't bleed out the air from the system. There's a 17mm bolt/plug on the top thermostat housing. It's in front of the "L" on the intake manifold and the small black plastic plug wire cover. That's where the coolant should be filled to purge out any major air pockets. Then the overflow bottle will purge out minor air pockets with the cap off and engine running.

Thanks - I will check this in the morning. This seems most logical to me so far, since the car did not *ever* overheat (or come close) before the shop replaced the thermostat. Seems an odd coincidence that the radiator would just up-and-fail right at that time. I know they refilled the coolant afterwards (would have had to at least top it off) and I watched the tech pour coolant in the overflow bottle...I don't recall seeing him do anything with a plug on the top of the engine...

[fooldall]

Like the guys said, very common once the system is sealed back up to overlook the backflush. Suprised they missed that though- I'd think about switching mechanics if this turns out to be the issue..

[djhillssc]

Possible they didn't bleed out the air from the system. There's a 17mm bolt/plug on the top thermostat housing. It's in front of the "L" on the intake manifold and the small black plastic plug wire cover. That's where the coolant should be filled to purge out any major air pockets. Then the overflow bottle will purge out minor air pockets with the cap off and engine running.

Thanks - I will check this in the morning. This seems most logical to me so far, since the car did not *ever* overheat (or come close) before the shop replaced the thermostat. Seems an odd coincidence that the radiator would just up-and-fail right at that time. I know they refilled the coolant afterwards (would have had to at least top it off) and I watched the tech pour coolant in the overflow bottle...I don't recall seeing him do anything with a plug on the top of the engine...

OK, hopefully we've got it licked. Did as you suggested and when I opened the plug on the top of the manifold...I could see the thermostat...dry. Started the car, and let it idle with the heater running and poured in coolant. It took about 1.5 quarts to fill it up. Then replaced plug, took cap off the overflow bottle and let it run for a few minutes.

I'll let you all know how it goes!

Thanks much!

D

[djhillssc]

Unfortunately, filling the coolant properly did not resolve the problem. So the facts again are:

1. Overheats primarily at freeway speeds, though it's getting worse. Now will overheat on the freeway without the A/C on...and the weather was 15 degrees cooler today here than it was last week.

2. Coolant is full, and filled properly at the block to ensure no air is in the cooling system.

3. Hydraulic fan works properly, and "speeds up" to full bore when it should.

4. Has a new thermostat.

5. Never overheated before the shop put in the new thermostat (which has now been replaced twice in the last week).

Perhaps (as suggested by some) it is the radiator that needs replacing. Or maybe the water pump isn't circulating the coolant well enough?

I just want to make sure before I spend a bunch more money that it's not something simple that the shop screwed up or overlooked when they replaced the thermostat.

Any advice is much appreciated! At this point my plan is to take the car into a shop that can test the radiator and water pump.

Thanks much to all who posted, or post ideas from this point too!

Dan

[mehullica]

If you can get a infrared thermometer that would be great, measure the top and bottom of the radiator to see if working. Then measure the temp of both hoses coming in and out of the engine. If all this happened after the thermostat R&R I would suspect it could be a crap-!Removed! quality thermostat. Or air still in the system. I would run the car with the cap off for at least 10 minutes at 1000-1500 rpm with the heater on to ensure all the air is out.