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Discussion Starter #1
I bought a 2001 Spyder today to replace my 2006 that someone tried to make a left hand turn through last month. I drove from Atlanta to Orlando to see the car. Stayed overnight with family in Tampa, then drove the 100 miles to Orlando this morning. I had high expectations for the car based on the seller's description and the pictures. I got there and was not disappointed. The car was clean inside and out. The engine bay looked good - like it has been tended to. The seller does none of his own automotive work (in fact, doesn't seem to know a lot about the mechanical stuff) but has had the car serviced by a local Toyota dealership for the four years that he's owned it. And the car only has about 65,000 miles on it. The price was right, so I bought it.

After the transaction, I started to drive the car back to Tampa. About 30 miles into the trip, I noticed the temperature gauge was reading much too high - not enough to overheat, but enough to know that something was definitely wrong. The temperature needle on my 2006 was always horizontal, right in the center of the band, which is where this one was while I test drove it and for the beginning of my trip. Now it was just above the 3/4 point.

I turned on the cabin heater full blast and the temperature immediately dropped to just above what I would expect to be normal for this car. I pulled off the highway at a truck stop a few miles down the road to investigate.

I checked coolant level and it was at the full mark - bright orange with no indication of contamination in the bottle. I checked the oil and there was no indication of coolant in the oil. I checked the exhaust with an inspection mirror and there was no water vapor or oil vapor in the exhaust. Also, the car was performing as I would expect an MR2 to perform (with the exception of the temperature), so there was nothing to suggest a head gasket issue.

I pulled the liner and spare tire tub out of the trunk and observed the cooling fans running. They work fine. There was no indication that air flow through the radiator is blocked.

The entire exhaust was recently replaced due to a restricted catalytic converter. The precats were removed and the new exhaust was installed by the dealership service department. Also, the ambient temperature in the engine bay was lower than I expected. (with my 2006, I wouldn't be able to rest my hand on the sheet metal beside the exhaust with it running. This one I could.) I think I can rule out a restricted cat.

With the heater running wide open in the cabin, the temperature was fairly stable, maintaining in a safe band between what would normally be normal and about 3/4. The air blowing in through the heater was very hot, suggesting the water pump is working fine.

I drove the car the rest of the way to Tampa, making the 100 mile trip with the heater on and the temperature maintaining as described above. The car performed fine the whole way at speeds between a crawl (rush hour, construction zones, etc) and 65-70 mph. Most of the way I ran about 60 mph.

Given all that, my diagnosis is a bad thermostat. Does anyone disagree? Have I missed anything? Something else I haven't ruled out?

I don't have the tools or the space to replace the thermostat here in Tampa, so I'm looking at making the 500 mile drive home the same way I got it here unless I can find a shop that can do it tomorrow.
 

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If you have the bleed hoses (two) I would check that there is no air in the system first. I just purchased a new rad for mine as the original is starting to crumble.
 

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Discussion Starter #4
Could be a partial blockage in the radiator or system cooling tubing too.
This is true, but very rare in my experience. (In fact, I've never personally seen it happen.) Is this a thing with the MR2's? Something I should expect? Aside from someone adding stop-leak to the coolant system, I can't imagine how it would happen. Should I consider it as a viable possibility?

Thanks for the reply.
 

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If you have the bleed hoses (two) I would check that there is no air in the system first. I just purchased a new rad for mine as the original is starting to crumble.
I'm not familiar with the bleed hoses? Where are they located? What do they do?

Thanks.
 

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Watching this thread with interest. I've never had a problem with mine running hot, the needle stays right in the middle like you originally mentioned. However, now that I'm running an OBD2 bluetooth link to a tablet with a spread of digital gauges, I see that my normal running temperature is actually 190-195 F. To me, that's too hot - I think it should be around 180.

Am I wrong about that? I recently had the water pump replaced with a 2ZZ and I have an underdrive pulley on it, but I had the digital gauges before that and the temps have remained the same. Whole system was flushed and filled with Toyota 50/50 pink coolant.
 

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This situation is consistent with a stuck thermostat, and that would be the first thing to replace. If the thermostat does not improve things, then it is time to look for obstructions.

You do not want to gamble with overheating your engine. You can greatly reduce its lifespan, even if there are no immediate consequences. I would park the car until you resolve this.
 

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I'm not familiar with the bleed hoses? Where are they located? What do they do?

Thanks.
There are two bleed vents, one for the heater and one for the rad. Toyota included two clear hoses rolled up, I believe under the front plastic shield (been a long time). When I used the hoses during a coolant change they where collapsed and not venting well, close to useless but managed. The hoses are attached to the vent valves and elevated high then valves opened, level ground is required. It may not resolve the issue but is a free check for air blockage which can cause cooling temp issues. I would also check the rad hoses for temperatures, both should be very warm just before the fan comes on, care for safety is advised. My ODBII reader gives the operating temp which is nice to see an actual number.

Personally I would not drive any distance with this problem. I did so 45 years ago and ruined a head gasket. The system circulates water through the heater circuit while the themo is closed with the water pump pushing coolant to the rear of the block. I don't know if checking for heat at various hoses will help any, most are inaccessible from the top.
 

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Watching this thread with interest. I've never had a problem with mine running hot, the needle stays right in the middle like you originally mentioned. However, now that I'm running an OBD2 bluetooth link to a tablet with a spread of digital gauges, I see that my normal running temperature is actually 190-195 F. To me, that's too hot - I think it should be around 180.

Am I wrong about that? I recently had the water pump replaced with a 2ZZ and I have an underdrive pulley on it, but I had the digital gauges before that and the temps have remained the same. Whole system was flushed and filled with Toyota 50/50 pink coolant.
You have to understand that coolant comes out of the head hotter than it goes into the pump inlet (at the thermostat housing). Coolant pumps are designed to provide enough flow so that at full load there is roughly a 10degrees C temp rise from inlet to outlet of the engine. If the coolant is leaving your head at 195, then it is going in at roughly 182 at full load. Your OBD2 temp sensor is in the head, so it is close to the coolant-out temp.
 

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There are two bleed vents, one for the heater and one for the rad. Toyota included two clear hoses rolled up, I believe under the front plastic shield (been a long time). When I used the hoses during a coolant change they where collapsed and not venting well, close to useless but managed. The hoses are attached to the vent valves and elevated high then valves opened, level ground is required. It may not resolve the issue but is a free check for air blockage which can cause cooling temp issues. I would also check the rad hoses for temperatures, both should be very warm just before the fan comes on, care for safety is advised. My ODBII reader gives the operating temp which is nice to see an actual number.

Personally I would not drive any distance with this problem. I did so 45 years ago and ruined a head gasket. The system circulates water through the heater circuit while the themo is closed with the water pump pushing coolant to the rear of the block. I don't know if checking for heat at various hoses will help any, most are inaccessible from the top.
Find the factory shop manual for filling the cooling system and you will understand the function of the bleed hoses.
 

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I see that my normal running temperature is actually 190-195 F. To me, that's too hot - I think it should be around 180.

Am I wrong about that?
The thermostat starts opening at about 180, but isn't fully open until about 195 F, so you gauge reading seems normal. The fan should not come on until about 199 F
 

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Interested to see where you get with this as i have a similar issue, if i get any progress on mine i will report back but ive now changed the thermostat and bleed the life out of the system and yet it still sits around 95c/203f as it always has since i got it as a standard car 18 months 8k miles ago including some trackday!, only reason im looking to sort it as im now turbo'd and want coolant system to be working perfectly which i beleive is to sit around 85c/185f under normal usage.
 

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Interested to see where you get with this as i have a similar issue, if i get any progress on mine i will report back but ive now changed the thermostat and bleed the life out of the system and yet it still sits around 95c/203f as it always has since i got it as a standard car 18 months 8k miles ago including some trackday!, only reason im looking to sort it as im now turbo'd and want coolant system to be working perfectly which i beleive is to sit around 85c/185f under normal usage.
See my recent post.... where in the engine do you expect to see 85C? The thermostat in our engines is in the coolest location. The temp sensor is not.

Dave
 

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See my recent post.... where in the engine do you expect to see 85C? The thermostat in our engines is in the coolest location. The temp sensor is not.

Dave
Measured by the temperature sensor on side of the head as other have found is the case on these, have you found different ? thermostat is 82c which is when its fully open but is flowing coolant before that point to try keep stable temperatures.

Im curious as to what temp (at engine) others find the outlet from radiator heading back towards engine starts to get warm/hot, i cant get mine to do much below 98c at the engine which is why i thought thermostat was stuck closed until that point! changing the stat and testing its opening at 82c which both new and old are didnt change this, these temps are measured both via the OBD and my Link G4 ecu which share stock temp sensor, im going to change out the temp sensor next to rule that out as maybe the temps are actually ok but sensor is not giving correct numbers!.
 

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A few things to keep in mind:

A thermostat is not an extremely sensitive device, due to its mechanical expansion technology. The thermostat has to run through a temperature range, maybe 10C, just to respond to the full range of load. The actual temperature range will be even larger due to gradients in the engine. You can only expect a typical operating temperature for specific conditions of load and speed.

A lot of cooling is done by the radiator and heater pipes that run the length of the car. The heater pipes provide cooling even when the heater is off. All of the MR2s have had a large excess of cooling capacity, and it can be difficult to get the radiator hot for demonstration purposes.
 

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Yes indeed the thermostat is a very primitive device and amazing it works as well as it does to keep engine temps in a fairly small window considering everything that is going on!, it maybe there is nothing wrong with my setup and certainly as its ran about 8k miles and maybe dozen times on track over that without issue show cooling system seems more than capable even if not using the fully circuit.

My concern is that my car isnt circulating the coolant through the radiator by time fan comes on at 92c, so fan has no effect in cooling down the engine, if i disable the fan and heat car up stationary by holding fast idle (wont go above low 90's if i dont increase revs) until i see 98c+ at the engine then coolant starts to flow through the whole system but doesnt drop the temperature at the engine at all, if i switch fan on at this point it cools rad down fast and coolant stops circulating but engine temp doesnt change!...its weird and hence suspecting it might be the temp sensor but after that im kind of stumped!

If my temp sensor is say 10degrees out then that would make sense but it seems to work pretty consistently and in past on other cars ive not seen one fail like this, they are usually miles off correct or dont work at all in my experience but it is a possible that its just slightly out i guess and need to test more on that,
 

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Ok i think ive found the issue on mine.......simple as the coolant temperature sensor reporting higher temp than it actually is it would seem!

Swapped out sensor for a spare used sensor i had and went for a good test drive, now car sits around 89-90c no matter what i do as in hard pulls on boost, sat in traffic or cruising along gently, occasionally over the 40minute test drive it spiked to 92c but soon dropped back down to 90 again, fingers crossed im sorted!

Ive not seen a temp sensor fail in this way before, as in just reading a few degrees over the actual temp and not miles off like they usually do, still you live and learn i guess!
 

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I'm all in with RM. Do not rely on this limp home feature you invented. You can toast this head gasket before you react to the Temp Gauge in stock OEM trims.

Compare the flow rate of your thermo choice as some have low specs, some open wider and provide more flow.

If you find corrosion inside the therm's case then think about checking radiator petcocks and drainage valves at bottom of rad.

My Mr2 Mk1 has a two stage (high/low stock) fan. Relays in front fuse box controls the kick-up from the ECU.

Is this a issue with this Mk3?
 
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