danci1973

Recently my Boxster 986 2.7 had the coolant pump replaced as the old one sprung a huge leak. Later, I was told that the plastic impeller disintegrated as well...

Now I have a feeling that the engine is running hotter then before - as far as I can remember the temperature gauge was pretty much always in 12 o'clock, straight up position.

Now it seems to wander over that, like that or even more:



I hooked up an OBD-II adapter and the most I've seen was 106 °C (222 °F) in slow, urban traffic with ambient temperature about 30 °C (86 °F).

On open roads the temperature hovers around 95-99 °C (203 - 210 °F) depending on speed and on highway with speeds over 130 km/h (80 mph) it's around 90 °C (194 °F) but takes a loooong time to drop if it was hotter before.

Ambient was about 30 °C all the time.

Are these normal temperatures or should I be worried?

paulofto

Those temps do seem high. Are your front radiator fans kicking in? They should come on when the temp exceeds 190F or about 90C. They should come on when you turn on your a/c as well. The fact that the temp drops when you are moving faster might mean that air is not flowing through the rads when you are moving slow, hence the fans may not be coming on.

Macster

Did the tech back flush the cooling system to remove any possible impeller debris that might have gotten into the engine or the radiators when the impeller failed?

Based on what you have posted I don't think debris is a problem, however.

The temperature getting up to 222F in slow urban traffic on an 86F day is about par for the course in my experience with my 2002 Boxster.

I've actually observed slightly higher coolant temperature. The highest I've ever seen it is 226F and this was in 116F amibent temperature and at other times on cooler days but when pushing the car hard on mountain roads.

The rest of the coolant temperature readings vs. road speed vs. ambient temperature is about right based on my experience.

When I encountered 116F ambient temperature in southern AZ and the intake air temperature was 135F, the coolant temperature was 226F -- and both fans running at high speed -- and I forget where the temperature gage needle was I was very concerned about the coolant temperature.

Back home -- in the KC MO area (and with the car running just fine which should have told me there was no problem) -- I touched base with the SM at the dealer where I had bought the car. He submitted the temperature conditions to the factory and the word from the factory was as long as there was no warning lights on from either too high coolant temperature, low coolant fluid level, or low oil pressure, there was no problem. Essentially this told me the in-dash temperature gage is for show.

Might mention I have seen the coolant temperature reach 226F at other times. The one time I particularly remember was when I was pushing the engine real hard on a mountain road on a day with the ambient temperature in the high 80's low 90's.

Was the T-stat replaced along with the water pump? It is always a good idea to replace the T-stat. They generally outlast the water pump but may not last the life of replacement pump. (My Boxster's water pump lasted 172K miles. The replacement pump has 130K miles on it.)

If the T-stat was not replaced it could be (could be) becoming slower to react to the coolant temperature changes or possibly not opening as far as it was before. I'm really not sure how a T-stat degrades.

If the T-stat was replaced the replacement could react to coolant temperature differently.

I sort of think this is the case with my car and the replacement T-stat. After the water pump/T-stat replacement I noticed the temperature gage needle position a bit higher a bit further to the right than before. Not a lot but the difference was noticable. But the 226F coolant temperature in AZ was with the orignal T-stat and the more recent 226F coolant temperature was with the new T-stat so regardless of any possible differences between the two T-stats the new one is not restricting coolant flow at the higher temperatures. The 226F coolant temperature then is where the engine's heat output is matched by the car's cooling system heat shedding capability.

Couple of things: Be sure the radiator ducts are free of trash. While it has been my experience even with a lot of plant trash present cooling is unaffected these should still be kept clean of trash build up.

Also, be sure the heavy rubber radiator ducting material is properly positioned. I have found now two times for some reason the leading edge of this can somehow move out of position and hang down into the radiator opening. The first time I was able to push this back into position with my fingers. But I was unable to do that this time and I keep forgetting to run the car by the dealer to have a tech do this.

The radiator electrical wiring and especially the special resister wants to be properly mounted/secured. My tech buddies tell me often when a car comes in this wiring/resister instead of being properly secured is shoved/jammed up in between some plastic panels. This is wrong. The resister wants to be mounted correctly to receive air flow to help keep it cool. But it doesn't want to be exposed to possible road water splash as this can damage the resister.

Next with the A/C off be sure both radiator fan motors come on low speed at the same time when the temperature reaches -- in the case of my 2002 Boxster 2.7l car -- at 212F. The fans should run until the coolant temperature reaches 205F.

You can cause this by driving the car around town until the engine is fully up to temperature then on your driveway rasing RPMs to say 1500 and holding until the radiator fans come on and noting the coolant temperature.

If the coolant temperature continues to climb the fans are switched to high speed when the coolant reaches 216F and are shut off when the coolant temperature reaches 205F.

Please note it is important the fan motors come on but you must check to ensure both fan motors are moving about the same amount of air. And to be thorough the exhausted air is the same temperature. You can use a digital thermometer to check the air temperature from both radiators.

In one case believe it or not -- this with my 2003 Turbo -- the passenger side radiator fan motor shaft snapped. The motor still ran but of course the fan was not spinning and no air was being pulled through the condenser/radiator.

Another time the driver side radiator fan motor while spinning the fan was not moving nearly as much air. The tech checked and found no fan stage errors but found the driver side fan motor was drawing more current than the other and I had him replace the fan motor.

Back to the Boxster: I have had one radiator fan motor "fail" -- that is fail to come on at low speed -- and this was addressed by either the tech replacing the resister or by replacing the fan motor. I can't recall now what the tech did.

Bottom line is the temperatures vs. operating conditions vs. ambient temperatures are about "normal" based on my experience/observation, but you want to make sure everything is operating correctly, the fans work right, the radiator air ducting is positioned correctly, etc.

danci1973

Many thanks to both of you...

Yes, fans are kicking in, albeit I'll have to check if they both do. I'll also have to check if the radiators are dirty.

I don't know if the system was back-flushed, however they did comment that 'it was a mess and a pain to get all that out of there'. I guess they would've known what to do.

The T-stat has been replaced, the new one is 83 °C (181 °F) type. Not sure what the old one was...

I also had them replace the coolant reservoir as the old one was quite 'yellowed' and opaque.

Macster

The old T-state was probably the same as the new one.

Yesterday it was pretty hot here. 97F or thereabouts. I didn't take a pic but the temp gage needle in my Boxster got nearly to the same location as the needle in your pic. I didn't bother to check the coolant temperature with my OBD2 code reader/data viewer.

Just a head's up: The coolant cap can leak vapor. As a result the coolant level will drop over time. With my Boxster and me using it almost every other day it took about a month for the level to drop enough to trigger the dash warning light.

This after the light had come on earlier and added around a gallon of distilled water to bring the level back up to where it wanted to be.

My advice is if the cap is original, or is "old", replace the cap with a new one. Last time I checked the newer cap comes with a part number that ends in "02" or "04".

Really I don't think you have anything going on to be worried about. Just keep an eye on the coolant level and half an eye on the coolant gage. You need to do this regardless.

If you ever start to see the needle moving up over to the right and continuing to move to the right look for a place to safely pull off the road and shut off the engine. The only time I've had to do this was when I hit some road debris late at night and busted a radiator. I could see coolant vapor trailing behind the car and knew what I was in for. In fact now I'm not sure the coolant needle moved all that much. I do know at some point the coolant warning light came on probably due to the coolant level dropping.

Rennzenn

I had a very similar situation with my 996... Pump went, flushed lots, replaced pump, pretty good til days got hot, then temps got about the same range as yours. That was followed by finding oil in the coolant. It's either a cracked head or fails head gasket, likely because of a hot spot caused by an impeller piece. Shoulda back-flushed again. Now I'm dropping the engine for a rebuild. Maybe I'll get ported & polished heads out of this.

Macster

Enough 996 heads have cracked without having gone through a failed water pump impeller and possible partial coolant blockage.

More often I suspect what happens is if the crack isn't due to material fatique, or casting inclusions, the cooling system has a leak that allows pressure to bleed away. It is pressure that prevents the hot coolant from flashing to steam. If this pressure is not sufficient then at the hottest spots -- around teh exhaust ports -- the hot coolant will flash to steam and this steam blocks coolant flow and the area gets super hot and a crack (or worse) is the result.

Still, I can't argue with any real conviction that the OP can't have a problem with impeller debris in his engine's cooling system.

While the coolant temperature is not that uncommon, the early Boxster cooling systems were adequate but only barely, but given the OP's engine cooling system suffered a failed impeller with all that can bring it may be worth the expense for the peace of mind to bring the car in and have the cooling system back flushed, both the engine and the radiators.

The shop should know how to do this. My WAG is the T-stat needs to be removed along with of course the water pump. The flushing must be a true "back" flush the goal is to obviously force water through the cooling system the reverse direction the water pump forces the coolant to remove any impeller debris.

Ideally this wants to be done as soon after the impeller failed and the amount of debris obtained from the filtered coolant and back flush water "matches" the amount of impeller material missing, as best as can be determined.

The only other way this material can be possibly removed is to remove the engine from the car, completely disassemble the engine and send the block and heads (with block and heads stripped of all hardware, seals, o-rings, gaskets, plugs, etc.) out to be subjected to some chemical bath that doesn't harm the aluminum but dissolves the composite plastic material that is suspected of being in the engine.

The shop may even have some kind of custom adapter plate to bolt a plate to the head's combustion surface and force the chemical through the coolant passages to perform a mini-back flush with this chemical to facilitate the removal of all the possible debris.

Because of all an impeller failure brings with it, this is why I stress if anyone suspects a water pump has failed, and if the pump is making noise or has excessive play (which probably accounts for the noise) or is leaking the pump has failed -- he should avoid running the engine any and ASAP get the car *flat bedded* to a shop and get this taken care of. It is not worth risk to try to milk even another mile out of the failed water pump.

Schnell Gelb

A long shot but worth a try - a common place for larger impeller debris to accumulate is the oil/water heat exchanger on top of the engine. Buy the 2 "o" rings and remove it. I found plastic impeller bits in mine .The P.O. had done a schlocky w/p & t-stat replacement just before i bought the car. The engine failed soon after.
For this reason I favor the metal impeller but only if you are super vigilant about testing the w/p bearings frequently. A wobbly metal impeller is a very effective boring tool to carve out the c/s half !

danci1973

I visited the shop that replaced the pump today and they said they did a back-flush and got all the impeller pieces out - they still had my old pump and all the pieces there, so we were able to 'reconstruct' the impeller and nothing was missing...

I guess I'm just a bit paranoid...

Macster

That the impeller debris was fully accounted for is good news.

If there was a local blockage the coolant temperature would very likely *not* be elevated but lower than "normal" (but probably not enough to raise any concern in this regard) and remain so until the engine suffered from the localized overheating by losing its head gasket or the head suffering from a crack.

Given all the "bad news" regarding these cars avoiding becoming paranoid is a full time job.