94 SL2 Overheating

In article >, "Andrew E." > wrote:
>Hi
>
>>> I have a 94 saturn SL2 that's overheating. So far I've done the following:
>>>
>>> 1. The coolant doesn't leak
>
>> How did you determine that? Just checking for drips underneath the car isn't
>> enough -- for example, a leaking head gasket could leak coolant into the
>> combustion chambers where it will be evaporated and blown out the tailpipe,
>> and you'll never see any drips. Have you verified that the cooling system
>> actually is, and remains, full?
>
>Yes it remains full over several months.
>
>>
>>> 2. The radiator is new
>>
>> Why?
>>
>
>Because my other radiator cracked and I had to replace it.

Why did it crack? Overheating, or some other cause?
>
>>> 3. Connected the radiator fan to the battery and the fan spins
>>> 4. Had a mechanic look at all the fuses and relays, all are fine.
>>> 5. Had three mechanics told me that it's the temperature sensor (one of
>>> them)
>>
>> I doubt it.
>>
>> It's possible that a failed temperature sensor is causing overheating by
>> preventing the electrically operated fan from coming on
>
>This is exactly what is happening. The fan doesn't come on even when the
>temperature indicator on the dashboard is way over half. As I said, the
>fan is fine and the relays and fuses have all been tested (by a
>mechanic) and are fine. If the relay is shorted the fan turns on.

Depending on which terminals are shorted, that may or may not be a valid test.
>
>-- but as long as the
>> vehicle is moving at any appreciable speed, there's enough air being forced
>> through the radiator that the fan isn't really needed for cooling, so this is
>> unlikely IMO unless you're doing a lot of driving in very heavy stop-and-go
>> slow speed traffic.
>
>This is exactly when the overheating happens: during stop and go
>traffic. If I'm driving at an appreciable speed the engine stays at the
>1/4 mark.
>
>>The more likely symptom of a failed sensor is a gauge
>> that's *falsely* reporting the engine to be too hot, when the temperature is
>> actually normal.
>>
>> IS the engine actually overheating? (Noticeably hotter than normal when you
>> lift the hood, smell of hot coolant, wisps of steam drifting out from under
>> the hood, clouds of steam pouring out, etc.)
>>
>
>Yes I've had it steam up before and it is *very* hot otherwise.
>
>> If so, I'm betting the problem is a failed thermostat. *Especially* if the
>> thermostat wasn't replaced at the same time the radiator was. (It should have
>> been. They're cheap, and they fail fairly regularly in older vehicles. As long
>> as the cooling system is drained anyway, it's just silly not to replace it.)
>>
>>> So my question is as follows:
>>>
>>> My Hanes manual says that I should replace the thermostat.
>>
>> I agree. :-)
>
>So given the above do you still agree?

Maybe not -- but I'd sure check it anyway. It's an easy test to perform.
>>
>> If you have the same Haynes manual that I do, it's on pages 3-2 and 3-3.
>> Or you could look in the index under "Thermostat, check and replacement".
>>
>> The instructions for checking and replacing the temperature sensor are a few
>> pages later, listed under "Coolant temperature sending unit - check and
>> replacement".
>
>So is this what I'm looking for? Does the coolant temperature sending
>unit cause the engine fan to come on?

Not directly, no. The coolant temperature sensor, and the fan relay, are both
connected to the PCM (Powertrain Control Module). That's what causes the
fan to come on. It's possible that a failure in the PCM, or in the wiring
between the PCM and the fan relay, could be preventing the fan from coming on.

By the way -- the Haynes manual gives a detailed procedure for testing the
coolant temperature sensor, using an ohmmeter. It's in Chapter 6, Engine &
Emissions Control Systems, under "Engine coolant temperature sensor".
>
>>> Where would I get the part numbers for what I need?

Don't bother trying to find part numbers; there's no need -- just call up your
friendly neighborhood auto parts retailer and say "I need _____ for a 94
Saturn SL2. You got one?"

>> You should be able to find a thermostat for your car at just about any auto
>> parts store, or maybe even in the automotive department at Wal-Mart.
>>
>Does this apply to the coolant temperature sending unit?

You won't find that at Wal-Mart, I don't think... but I'd be really surprised
if the major auto parts chains wouldn't have it.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.

On Fri, 22 Sep 2006 23:33:04 GMT, "Bob Shuman"
> wrote:

>From what you state, it sounds like either a failed coolant temperature
>sensor or the fan relay.


Or the wiring between them. Also there is two temp sensors on that
year engine. One for gage and one for ECM/PCM (engine control module
or powertrain control module which ever you prefer to call it) The
second one is used to control fan.
-----------------
TheSnoMan.com

Hi,

Yes this is exactly what two mechanics told me. But I don't see anything
in the hanes manual about two sensors. Do you know where they are located?


Thanks,
Andrew

SnoMan wrote:
> On Fri, 22 Sep 2006 23:33:04 GMT, "Bob Shuman"
> > wrote:
>
>>From what you state, it sounds like either a failed coolant temperature
>> sensor or the fan relay.
>
>
> Or the wiring between them. Also there is two temp sensors on that
> year engine. One for gage and one for ECM/PCM (engine control module
> or powertrain control module which ever you prefer to call it) The
> second one is used to control fan.
> -----------------
> TheSnoMan.com

On Fri, 22 Sep 2006 17:17:04 -0400, "Andrew E."
> wrote:

>Hi,
>
>I have a 94 saturn SL2 that's overheating. So far I've done the following:
>
>1. The coolant doesn't leak
>2. The radiator is new
>3. Connected the radiator fan to the battery and the fan spins
>4. Had a mechanic look at all the fuses and relays, all are fine.
>5. Had three mechanics told me that it's the temperature sensor (one of
>them)
>
>So my question is as follows:
>
>My Hanes manual says that I should replace the thermostat. Is the
>thermostat the same as the temperature sensor? If not are there
>instructions on replacing it?
>
>Where would I get the part numbers for what I need?
>
>
>Thanks,
>Andrew


From your description, remember I am not there to do the work, so this
is all guessing, and isn't a How-to:

Something with coolant flow must be happening. If you have a fan
comeing on, and coolant level is sufficent, I would suspect coolant
flow is the issue.

I would check the water pump for operation, the dumb way I would do
it, is check if I get heat (strong heat) from the heater. Second, I
would then figure what could be interupting flow, and the internal
coolant thrmistat (a valve that opens and closes allowing flow to the
radator). I would be suspect of that, since I've been told they fail
over time.

I was once told how to check one, a valve thermistat, but figured that
once I open the housing, it saves time to just install a new one.

If a person can safely work yourself, and follow directions from the
Haynes book, I like them better than chiltons, since more pictures.
A person could replace the item themself.

later,

tom @ www.NoCostAds.com

Hi,

So now I have replaced the temp sensor. It had a crack in it and was
misreporting the temperature. So now when the car's temp gauge gets to
3/4 the fan comes on and the engine cools down.

Here's the rub. I've had this car for 3 years and it's never gone beyond
the 1/4 mark on the temp guage. So now I'm thinking that I might have
misdiagnosed the problem. The temp guage was definitely cracked and
broken, but I didn't realize that the car had to be at 220 degrees (3/4
of the guage) before the fan would come on.

Do you think this is a thermostat problem as you originally suggested?
I read the thermostat "Check" portion in the hanes manual and it says if
the upper radiator hose is hot then it's not a thermostat problem.

So I could just ignore the fact the engine gets to 3/4 of the temp guage
because the fan will come on and cool it before it overheats.

Any suggestions?

Thanks,
Andrew

Doug Miller wrote:
> In article >, "Andrew E." > wrote:
>> Hi
>>
>>>> I have a 94 saturn SL2 that's overheating. So far I've done the following:
>>>>
>>>> 1. The coolant doesn't leak
>>> How did you determine that? Just checking for drips underneath the car isn't
>>> enough -- for example, a leaking head gasket could leak coolant into the
>>> combustion chambers where it will be evaporated and blown out the tailpipe,
>>> and you'll never see any drips. Have you verified that the cooling system
>>> actually is, and remains, full?
>> Yes it remains full over several months.
>>
>>>> 2. The radiator is new
>>> Why?
>>>
>> Because my other radiator cracked and I had to replace it.
>
> Why did it crack? Overheating, or some other cause?
>>>> 3. Connected the radiator fan to the battery and the fan spins
>>>> 4. Had a mechanic look at all the fuses and relays, all are fine.
>>>> 5. Had three mechanics told me that it's the temperature sensor (one of
>>>> them)
>>> I doubt it.
>>>
>>> It's possible that a failed temperature sensor is causing overheating by
>>> preventing the electrically operated fan from coming on
>> This is exactly what is happening. The fan doesn't come on even when the
>> temperature indicator on the dashboard is way over half. As I said, the
>> fan is fine and the relays and fuses have all been tested (by a
>> mechanic) and are fine. If the relay is shorted the fan turns on.
>
> Depending on which terminals are shorted, that may or may not be a valid test.
>> -- but as long as the
>>> vehicle is moving at any appreciable speed, there's enough air being forced
>>> through the radiator that the fan isn't really needed for cooling, so this is
>>> unlikely IMO unless you're doing a lot of driving in very heavy stop-and-go
>>> slow speed traffic.
>> This is exactly when the overheating happens: during stop and go
>> traffic. If I'm driving at an appreciable speed the engine stays at the
>> 1/4 mark.
>>
>>> The more likely symptom of a failed sensor is a gauge
>>> that's *falsely* reporting the engine to be too hot, when the temperature is
>>> actually normal.
>>>
>>> IS the engine actually overheating? (Noticeably hotter than normal when you
>>> lift the hood, smell of hot coolant, wisps of steam drifting out from under
>>> the hood, clouds of steam pouring out, etc.)
>>>
>> Yes I've had it steam up before and it is *very* hot otherwise.
>>
>>> If so, I'm betting the problem is a failed thermostat. *Especially* if the
>>> thermostat wasn't replaced at the same time the radiator was. (It should have
>>> been. They're cheap, and they fail fairly regularly in older vehicles. As long
>>> as the cooling system is drained anyway, it's just silly not to replace it.)
>>>
>>>> So my question is as follows:
>>>>
>>>> My Hanes manual says that I should replace the thermostat.
>>> I agree. :-)
>> So given the above do you still agree?
>
> Maybe not -- but I'd sure check it anyway. It's an easy test to perform.
>>> If you have the same Haynes manual that I do, it's on pages 3-2 and 3-3.
>>> Or you could look in the index under "Thermostat, check and replacement".
>>>
>>> The instructions for checking and replacing the temperature sensor are a few
>>> pages later, listed under "Coolant temperature sending unit - check and
>>> replacement".
>> So is this what I'm looking for? Does the coolant temperature sending
>> unit cause the engine fan to come on?
>
> Not directly, no. The coolant temperature sensor, and the fan relay, are both
> connected to the PCM (Powertrain Control Module). That's what causes the
> fan to come on. It's possible that a failure in the PCM, or in the wiring
> between the PCM and the fan relay, could be preventing the fan from coming on.
>
> By the way -- the Haynes manual gives a detailed procedure for testing the
> coolant temperature sensor, using an ohmmeter. It's in Chapter 6, Engine &
> Emissions Control Systems, under "Engine coolant temperature sensor".
>>>> Where would I get the part numbers for what I need?
>
> Don't bother trying to find part numbers; there's no need -- just call up your
> friendly neighborhood auto parts retailer and say "I need _____ for a 94
> Saturn SL2. You got one?"
>
>>> You should be able to find a thermostat for your car at just about any auto
>>> parts store, or maybe even in the automotive department at Wal-Mart.
>>>
>> Does this apply to the coolant temperature sending unit?
>
> You won't find that at Wal-Mart, I don't think... but I'd be really surprised
> if the major auto parts chains wouldn't have it.
>

In article >, "Andrew E." > wrote:
>Hi,
>
>So now I have replaced the temp sensor. It had a crack in it and was
>misreporting the temperature. So now when the car's temp gauge gets to
>3/4 the fan comes on and the engine cools down.
>
>Here's the rub. I've had this car for 3 years and it's never gone beyond
>the 1/4 mark on the temp guage.

... probably because the gauge wasn't getting the correct input from the
faulty sensor.

> So now I'm thinking that I might have
>misdiagnosed the problem. The temp guage was definitely cracked and
>broken,

You mean the sensor, right?

> but I didn't realize that the car had to be at 220 degrees (3/4
>of the guage) before the fan would come on.

Considering that (according to the Haynes manual) the thermostat isn't even
fully open until 212, that's really not too surprising.
>
>Do you think this is a thermostat problem as you originally suggested?

Not anymore, no.

>I read the thermostat "Check" portion in the hanes manual and it says if
>the upper radiator hose is hot then it's not a thermostat problem.

Well, is it?
>
>So I could just ignore the fact the engine gets to 3/4 of the temp guage
>because the fan will come on and cool it before it overheats.
>
>Any suggestions?

Have you actually checked the upper radiator hose yet? If it's hot, then, like
the book says, the 'stat is OK -- and I was wrong. If it's not hot, then
replace the 'stat too.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.

Yes the upper hose is very hot.


Andrew

Doug Miller wrote:
> In article >, "Andrew E." > wrote:
>> Hi,
>>
>> So now I have replaced the temp sensor. It had a crack in it and was
>> misreporting the temperature. So now when the car's temp gauge gets to
>> 3/4 the fan comes on and the engine cools down.
>>
>> Here's the rub. I've had this car for 3 years and it's never gone beyond
>> the 1/4 mark on the temp guage.
>
> .. probably because the gauge wasn't getting the correct input from the
> faulty sensor.
>
>> So now I'm thinking that I might have
>> misdiagnosed the problem. The temp guage was definitely cracked and
>> broken,
>
> You mean the sensor, right?
>
>> but I didn't realize that the car had to be at 220 degrees (3/4
>> of the guage) before the fan would come on.
>
> Considering that (according to the Haynes manual) the thermostat isn't even
> fully open until 212, that's really not too surprising.
>> Do you think this is a thermostat problem as you originally suggested?
>
> Not anymore, no.
>
>> I read the thermostat "Check" portion in the hanes manual and it says if
>> the upper radiator hose is hot then it's not a thermostat problem.
>
> Well, is it?
>> So I could just ignore the fact the engine gets to 3/4 of the temp guage
>> because the fan will come on and cool it before it overheats.
>>
>> Any suggestions?
>
> Have you actually checked the upper radiator hose yet? If it's hot, then, like
> the book says, the 'stat is OK -- and I was wrong. If it's not hot, then
> replace the 'stat too.
>

In article >,
says...
> So I could just ignore the fact the engine gets to 3/4 of the temp guage
> because the fan will come on and cool it before it overheats.
>

3/4 is known to be normal.

Ok, so that said, why would have the car never gone to that? The sensor
that was cracked was the PCM sensor, not the guage... and the guage
never showed the car overheating before...


Andrew

BläBlä wrote:
> In article >,
> says...
>> So I could just ignore the fact the engine gets to 3/4 of the temp guage
>> because the fan will come on and cool it before it overheats.
>>
>
> 3/4 is known to be normal.

In article >, "Andrew E." > wrote:
>Yes the upper hose is very hot.

Then your thermostat's probably good, and the problem was indeed the sensor.
Everything should be OK now.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.