Overheating '93 - I Need Your Input

[Kitaka]

OK, I've read the posts on this topic, replaced all coolant hoses and water pump, bled the system several times (using the burp method), replaced the coolant bottle, and the motor still overheats at times.

The overheating seems unusual. The car can sit and idle all day long without a problem. When driving on local roads, not a problem. But, when driving at highway speed the temp will start to increase after about 20 minutes of driving. This problem only occurs during warm ambient temperatures (+85 degrees). The system operates fine during cooler periods. I noticed that once the temps rise to near the red zone at highway speed, and I disengage the clutch, the temps quickly rise. Engage the clutch again and the temps drop slightly..(as expected)..but still continues to rise over time. I eventually have to pull off the highway and park for a cool down.

It's as if the motor dreads a heat soak condition and can't recover from it. All cooling fans operate but I eliminated this concern because the system does not cool down at highway speed while coasting. I've pressure tested the cooling system and replaced the pressure cap.....yet the seasonal problem of overheating continues.....in an intermitted fashion. I can't find a source that sells kits that test for exhaust gasses in antifreeze. Maybe you can help on this one also.

So before I go and replace the thermostat, or radiator, what do you guys suggest is the fix?

 

[davidf]

A thermostat replacement is always a good idea if it's never been done. Thats probably your cheapest thing to try first. If it winds up being the radiator, LMK since I have a perfect 55,000 mile radiator in my garage. I'm in TX also so shipping is'nt a problem. You'll get the deal of the century if you need it.:wink:

 

[cparsons]

A thermostat replacement is always a good idea if it's never been done. Thats probably your cheapest thing to try first.

Yeah, what he said. Replacing the thermostat is like $25 in parts and takes an hour or two in your driveway. It's pretty easy...directions are in service manual.

 

[Thanhnsx]

When you do your future oil change. You can take a quick glance to make sure there isn't no coolant coming out with your oil.

 

[Larry Bastanza]

bled the system several times (using the burp method), replaced the coolant bottle, and the motor still overheats at times.

Please explain the "burp method".

Were all four bleed valves purged with full coolant flow?
What is the coolant level now?
Is it loosing any coolant?
I assume you did the timing belt when the W/P was replaced?
Did you follow the tensioning procedure for the timing belt?
Was the belt/WP done at a shop. or a DIY?

Regards,
LarryB

 

[SOURCE 1]

I am thinking a possible water pump.

 

[DutchBlackNsx]

I vote for the thermostat

 

[Zishan]

Driving with hot can damage the engine. (duh :smile Next time it starts warming up, turn the heater on full blast, the temp should drop while driving to about normal.

From what you've described, I would not recommend driving your car. But if you must, try the above mentioned, so your car doesn't overheat and limp it home or to the shop.

Also, try the thermostat. I think if your thermostat goes bad, your fans won't work. If your fans are working, it might not be the thermostat. Someone please correct me if I'm wrong... as I understand it, people change the thermostat(aftermarket) on certain cars so the fan kicks on at a lower temp(so the car runs cooler). Therefore the thermostat controls the fans?

Best of luck,
- Zishan

 

[angus]

Leaking H/G.

 

[usafdarkhorse]

Leaking H/G.

What I speculate as well. Try the thermostat though.

Let us know how it works out!

 

[drew]

If you are not losing coolant, then it probably isn't a head gasket.

It sounds like you have a flow issue....

1. Might be air in the system, bleed it.
2. Might be debris in the radiator fins/ducting
3. Take out the thermostat to see if it matters at all. Reinstall once you are done with the test.
4. Make sure none of the hoses are kinked (under the car, etc...)
5. I would borrow a friends radiator that needs their coolant changed and see if that matters. You might be able to get your radiator flow checked, but at some point a new one is cheaper than testing a perfectly good radiator.

If you could monitor the temperatures going into and out of the radiator, that would be a really good test.

Drew

 

[96cxt]

Driving with hot can damage the engine. (duh :smile Next time it starts warming up, turn the heater on full blast, the temp should drop while driving to about normal.

From what you've described, I would not recommend driving your car. But if you must, try the above mentioned, so your car doesn't overheat and limp it home or to the shop.

Also, try the thermostat. I think if your thermostat goes bad, your fans won't work. If your fans are working, it might not be the thermostat. Someone please correct me if I'm wrong... as I understand it, people change the thermostat(aftermarket) on certain cars so the fan kicks on at a lower temp(so the car runs cooler). Therefore the thermostat controls the fans?

Best of luck,
- Zishan

Going with a lower degree thermostat helps keep the engine temp lower but that doesn't turn on your fans. There is a fan switch on the thermostat housing that turns the fans on/off. You can get a lower degree fan switch to kick the fans on earlier.

There are many reasons as to why your car is heating up. I suspect that its your head gasket beacuse it's over heating under load. But before you start pulling the heads off flush your radiator and change out the thermostat and fan switch. You can get the lower degree ones from http://www.mishimoto.com/ they aren't that expensive, and make sure you dont have any air in your line when you fill the system.

Rahim

 

[davidf]

Driving with hot can damage the engine. (duh :smile Next time it starts warming up, turn the heater on full blast, the temp should drop while driving to about normal.

From what you've described, I would not recommend driving your car. But if you must, try the above mentioned, so your car doesn't overheat and limp it home or to the shop.

Also, try the thermostat. I think if your thermostat goes bad, your fans won't work. If your fans are working, it might not be the thermostat. Someone please correct me if I'm wrong... as I understand it, people change the thermostat(aftermarket) on certain cars so the fan kicks on at a lower temp(so the car runs cooler). Therefore the thermostat controls the fans?

Best of luck,
- Zishan

To this day of 2 years ownership, I've yet to see my rad. fan operate, ever. I know my condensor fans both work but my car has never ever had a heating issue. I have to go knock on wood now.:wink:

 

[nsxotic911]

Learn from me, having overheated and subsequently blown civic engine and a toyota pickup engine because of mucking with it, if you start seeing any overheating STOP MUCKING with it. Thankfully, haven't done so to the NSX.. yet.


TOW IT and I mean TOW IT to a good shop and start fresh. DO NOT TURN ON THE CAR.
1.) Bleed everythign properly, it's really hard to get EVERYTHING right, people overheat their engine all the time by missing a smalll detail - I almost did this.. I said almost folks.
2.) Go from there..

Again, TOW IT to Acura dealership or someone that knows what their doing with the NSX's. If they just say throw out parts until it works, that's the wrong shop to take it to.

They should either know exactly what they're doing, or be eyes deep into the service manual.

Test the thermostate first, test the radiator cap, check the bleeding.. pull any codes.. from a couple of years of diy'r home mechanic, I've learned that you should spend 5x the amount of time diagnosing before you turn on the car/start changing anything.

Good luck! If you come back with a blown engine because you continued to muck with it, I warned ya

PS: How do you know it's overheating? Are you pulling the temp from the ECU/engine or from the gauge. If the gauge, just so you know, it will be at least 230 before it goes passed the middle line, and that is extremely hot. If it goes at 260, which is very easy to do, and MAYBE the next line up, and if you've done this a couple of tiems, you're f'd. If it's gone 2+ above the middle line, you're f'd....

Did I mention not to turn on the car eyt?

PS: I noticed that you said it hit red a couple of times... well, I hate to say it, but your engine is likely screwed at this point. Do a comp and a leakdown test to see how bad, check for coolant in oil and vice versa....I'm with the other guys, probably a hg leak at this point

 

[nsxotic911]

To this day of 2 years ownership, I've yet to see my rad. fan operate, ever. I know my condensor fans both work but my car has never ever had a heating issue. I have to go knock on wood now.:wink:

The thermostat is a valve that controls whether coolant, after it's passed through the radiator, enters the engine. If the thermostat is closed, water coolant is inthe lines/radiator just sits there. Only after the engine is warmed up to the right temperature, and thus the thermostat opens, will water flow into the engine, and the engine push out the water towards the front of the car. Once the temperature hits based on the sensor, the radiator fan turns on. The water then stays behind the thermostat until it opens (if it closed) and cycle repeats.

This is how I undersatnd it

 

[drew]

This is how I understand it

Yes.

The thermostat's job is to keep the engine at its minimum temperature range. If an engine is too cold it will be very inefficient along with gunking up the oil passages (permanently starving the engine of oil).

The radiator is to make sure the engine does not exceed the maximum temperature range.

Like porridge you don't want it to be too hot or too cold, you want it "just right".

 

[davidf]

The thermostat is a valve that controls whether coolant, after it's passed through the radiator, enters the engine. If the thermostat is closed, water coolant is inthe lines/radiator just sits there. Only after the engine is warmed up to the right temperature, and thus the thermostat opens, will water flow into the engine, and the engine push out the water towards the front of the car. Once the temperature hits based on the sensor, the radiator fan turns on. The water then stays behind the thermostat until it opens (if it closed) and cycle repeats.

This is how I undersatnd it

Oh I know the process but you'd think in 2 yrs I'd catch it running. I even have the screen out of my VIS hood. Fortunately my temp stays rock solid all the time.:wink:

 

[Kitaka]

OK I changed the thermostat and the condition remains. in response to your suggestions I have already:

Bled the system (at all 4 points). confirmed that no water is in the engine oil, verified that the coolant tank is full, verified that the radiator fan comes on, there are no kinked hoses, radiator fins are clear and undamaged, and w/p tensioning was done during t/b replacement (a DIY project).

I plan to again pressure test the cap and system just to make sure. At this point my next step is to have the radiator rodded out. Any other ideas?

 

[DutchBlackNsx]

There are still a lot of questions in this thread left unanswered, especially Larry B's.

Just to add another question, did the problem just started to show, or did it got triggered after some event?

BTW, i got a free coolantsniff at me local Honda dealer. Its quick. Try that as well.

 

[goldNSX]

DITO: Larry's question point in the right direction. No answers so far.

As far as bleeding is concerned: If one ever looks in the manual bleeding is very, very simple. Moreover, for the remaining small amount of air after the procedure, the NSX system is self-bleeding.

I agree with DutchBlackNSX: a coolantsniff is fast and cheap and will save you from speculations about a $$$$-bill (HG). But Larry's questions first.

 

[ralph cerbone]

OK, I've read the posts on this topic, replaced all coolant hoses and water pump, bled the system several times (using the burp method), replaced the coolant bottle, and the motor still overheats at times.

The overheating seems unusual. The car can sit and idle all day long without a problem. When driving on local roads, not a problem. But, when driving at highway speed the temp will start to increase after about 20 minutes of driving. This problem only occurs during warm ambient temperatures (+85 degrees). The system operates fine during cooler periods. I noticed that once the temps rise to near the red zone at highway speed, and I disengage the clutch, the temps quickly rise. Engage the clutch again and the temps drop slightly..(as expected)..but still continues to rise over time. I eventually have to pull off the highway and park for a cool down.

It's as if the motor dreads a heat soak condition and can't recover from it. All cooling fans operate but I eliminated this concern because the system does not cool down at highway speed while coasting. I've pressure tested the cooling system and replaced the pressure cap.....yet the seasonal problem of overheating continues.....in an intermitted fashion. I can't find a source that sells kits that test for exhaust gasses in antifreeze. Maybe you can help on this one also.

So before I go and replace the thermostat, or radiator, what do you guys suggest is the fix?

ok lets start at begining,was it overheating before you serviced cooling systen?

 

[Larry Bastanza]

"I can't find a source that sells kits that test for exhaust gasses in antifreeze."

Block Tester:

http://cgi.ebay.com/ebaymotors/NAPA...id=p4506.c0.m245&_trkparms=65:1|39:1|240:1318

Works very well. You can also get this at any local NAPA store, and I am sure most autoparts stores have something like it.

And I am adding one more question, it was mentioned above:

When did this start to happen, after the timing belt job?

HTH,
LarryB

 

[ftuhy]

This almost sounds too obvious, but I'll suggest it anyway. Has airflow to the radiator been blocked by something? Paper, cardboard, basketball, large bird, etc etc. Did you change anything on the front bodywork, including possibly removing the lower black air dam if its stock bodywork?

The temperature on my NSX is so stable its almost ridiculous. Below freezing, idling, 100 mph on a hot day, ac on, ac off - its always at approximately the same spot on the gage. The only problem I ever had was a few years back the thermostat stuck partially open (the o-ring on the moving disk "mushroomed"). As a result it would take 10 or more miles to warm up in the winter. I replaced the thermostat and it now consistently warms up in 2 to 3 miles.

Hmmm. I wonder if the o-ring mushroomed on your thermostat, but flipped in the other direction, preventing it from fully opening?? Note that my replacement was a NAPA thermostat that doesn't use that internal o-ring -- its the only non-OEM part on my engine.

Honda is the only car maker I have seen that uses that internal o-ring. It seems to be a case of overdesign and an extra point of failure. Mine was not the first NSX with that specific thermostat failure.

Final note. I have a long, steep driveway. When I change my coolant and bleed the system, I do the extra step of parking it on the steep part of the driveway and then do a final bleed. I do this twice, once with the front pointing uphill and once with it pointing downhill. So, I'm a little anal about my favorite toy...........:wink:

 

[nsxotic911]

"I can't find a source that sells kits that test for exhaust gasses in antifreeze."

Block Tester:

http://cgi.ebay.com/ebaymotors/NAPA...id=p4506.c0.m245&_trkparms=65:1|39:1|240:1318

Works very well. You can also get this at any local NAPA store, and I am sure most autoparts stores have something like it.

And I am adding one more question, it was mentioned above:

When did this start to happen, after the timing belt job?

HTH,
LarryB

Larry, what does a block tester do and how does it work?

 

[Larry Bastanza]

You add a special fluid to the tester tube, which is blue in color. You install it onto the top of the coolant bottle. With the engine running, the tool has a squeeze ball that goes on top and will draw gases through the fluid in the tube. If the fluid turns yellow, you have combustion gases in the coolant. So yellow = pull engine, pull heads, do valve job, resurface heads, etc...

HTH,
LarryB