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In your starting post, you said:
The coolant level is correct, the temp needle reads slightly below the middle and the car has a great heater.
Now you say the heater works too well when the engine is cold, but not very well when the engine warms up. Some clarification would be useful.

The temp gauge should read a little below the mid-point when the engine is at operating temperature. If your gauge indicates normal temperature with cold coolant, the gauge may be faulty.

If you're judging coolant temperature by how well the heater is working, perhaps the problem lies with the heater. The heater core may have a problem.

If the coolant temperature is actually too low, check to see if the radiator fans are running. There are two fans: One for the A/C and one for the coolant. They don't come on very often. If either fan is running, it might cause the coolant to be over-cooled, but if that's happening, it should show up in the temp gauge reading.


Given only the info so far supplied, I'd say you have a genuine mystery.
 

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Discussion Starter #22
In your starting post, you said:


Now you say the heater works too well when the engine is cold, but not very well when the engine warms up. Some clarification would be useful.

The temp gauge should read a little below the mid-point when the engine is at operating temperature. If your gauge indicates normal temperature with cold coolant, the gauge may be faulty.

If you're judging coolant temperature by how well the heater is working, perhaps the problem lies with the heater. The heater core may have a problem.

If the coolant temperature is actually too low, check to see if the radiator fans are running. There are two fans: One for the A/C and one for the coolant. They don't come on very often. If either fan is running, it might cause the coolant to be over-cooled, but if that's happening, it should show up in the temp gauge reading.


Given only the info so far supplied, I'd say you have a genuine mystery.
The gauge reads a little below the mid point, as you say it should, once it's up to temp. The heater blows HOT when at idle/low RPM but not as hot, just hot enough actually, while at driving RPM. This is while the temp gauge is right below mid-point.

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I would be willing to bet the PO had this code and chased it replacing parts and sensors he finally pulled the T stat out or gutted it. That would cause the water to be hot during idle low rpm but as soon as you drive and rom increases the water flow is accelerated by the pump and cools down. After this didn’t clear the CEL code he sold the car. Now you get to add the t stat and replace the O2 and presto you have a great running car and the PO will one day discover he sold a good car because he didn’t use the wealth of info provided by this great group.
 

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Discussion Starter #24
I would be willing to bet the PO had this code and chased it replacing parts and sensors he finally pulled the T stat out or gutted it. That would cause the water to be hot during idle low rpm but as soon as you drive and rom increases the water flow is accelerated by the pump and cools down. After this didn’t clear the CEL code he sold the car. Now you get to add the t stat and replace the O2 and presto you have a great running car and the PO will one day discover he sold a good car because he didn’t use the wealth of info provided by this great group.
This is another possibility I've considered, or it may simply be a slightly stuck open thermostat. Either way I suppose it needs replacing. The engine runs great and the gauge needle stays where it should even while at highway speed. Went for an about 30 mile drive last night, at 30°,heater blew very warm but not HOT. If it were hot all the time as it is at low RPM it would be unbearable.

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The temperature gauge is not an accurate indicator of coolant temperature because it has a deadband that spans the normal operating range. I suppose that the idea of this was to prevent customer anxiety over normal temperature fluctuations. For whatever reasons, it will only show you too high to too low, and it will hide normal variations with speed or load.
 

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I would be interested in knowing what the OBDII shows for temps at idle and higher speed. I expect the temp sensor sends info to both the ECU and gauge. If I recall correctly the reader shows in the range of 180 degrees driving and I have to high idle awhile to get the fans on. The spyder seems to have a very good cooling system.
 

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Discussion Starter #28
Got both upstream sensors changed this morning, cleared the CEL then went for a 15 miles drive. Cap was correct, NO CEL!!!! Thank you very very very ~ Cap.
Less than $50 and 20 minutes saved me $$$.

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Discussion Starter #29 (Edited)
Now I'm getting code P0204 , indicating a catalyst problem. It doesn't have one, maybe that's the problem. LOL.
In the Volvo world we put a spacer on the rear O2, or have it tuned out,when going catless. Will a spacer take care of this?

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You mean a 420 ( Damn Dyslexia! )

Yes a spacer will work in the Toyota world as well
 
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