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Discussion Starter #1
This is a sequel to my earlier post here.

Just to refresh, I bought a 2001 MR2 Spyder in Orlando, Florida the weekend before last. I drove it to Tampa where my wife and I were staying with her aunt (we live outside Atlanta). During the 100 mile trip to Tampa, the engine started running hot. I turned on the heater full blast and the temperature settled out a little above normal. I stopped to check the car out and found everything I could see to be in good order:
  • coolant level was good; no sign of leakage and an attempt to "burp" the coolant system indicated no sign of air in the system
  • both cooling fans were working
  • no sign of coolant in the oil, oil in the coolant, or vapor of any kind in the exhaust (using a mirror); car performed as expected (the temperature notwithstanding), so no indication of a head gasket leak
  • exhaust (including cats) had recently been replaced, so no reason to suspect a backed up cat
  • air blowing from the heater was very hot, so coolant flow through the engine was confirmed
My diagnosis on the road was that the thermostat was bad. Since I was able to adequately control engine temperature with the cabin heater, I elected to drive the car the rest of the way to Tampa.

Without the space or tools to do the job myself, I brought the car to a local mechanic that my aunt and a friend of hers had used in the past. He is honest and knowledgeable so I turned my newly adopted baby over to him. The mechanic rechecked all of my troubleshooting steps and came up with the same diagnosis I had: faulty thermostat.

He replaced the thermostat. While he was in the neighborhood, he saw stains indicating leakage from the water pump. He sent me pictures and we agreed it was a good idea to go ahead and replace it while he was in there.

After replacing the water pump and thermostat, he refilled the system, dried the engine and bay out with compressed air, and checked the coolant system for leaks. He was surprised to see coolant leaking from two bolts that hold the engine mount to the block. (These are the two backed-out bolts you see near the vertical center of the attached photo.) He applied some RTV sealant to these bolts and the leaking stopped ... from there.

So here is my first question: I suspect these bolts penetrate the water jacket and, as a normal measure, must be sealed to prevent coolant leakage at that point. Is this the case? Or is something amiss here?

Moving on. After sealing those two bolts, the mechanic recleaned and rechecked for coolant leaks. He discovered a steady drip of coolant, but as of 9:30pm last night, he was still unable to find the source. He verified that it is not coming from the thermostat, the water pump, or the engine mount bolts mentioned above. There were no detectable coolant leaks when he received the car, which suggests the leak would be from something that was disturbed during the work.

Question number two: Does anyone have any idea where he might look for this coolant leak?

We need to get this car home and put it into service. Any input would be much appreciated. Thanks.

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Coolant should not make it to those bolts. This means that the front cover is not properly sealed to the block. Even with no visible external leaks, you might get coolant to leak into the oil. The only solution is to remove the front cover completely, clean all surfaces completely and reseal with sealant per the shop manual. Loctite or Permatex Ultra-Grey is a good choice for sealant.
Dave
 

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Discussion Starter #3
Coolant should not make it to those bolts. This means that the front cover is not properly sealed to the block. Even with no visible external leaks, you might get coolant to leak into the oil. The only solution is to remove the front cover completely, clean all surfaces completely and reseal with sealant per the shop manual. Loctite or Permatex Ultra-Grey is a good choice for sealant.
Dave
dblotii,

I just looked through the BGB and, based on what I'm seeing, I'm wondering if a leak between the water pump side of the cover and the timing chain side could also be causing the original cooling issue. I'd like to know your thoughts about that.

Thanks.
 

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dblotii,

I just looked through the BGB and, based on what I'm seeing, I'm wondering if a leak between the water pump side of the cover and the timing chain side could also be causing the original cooling issue. I'd like to know your thoughts about that.

Thanks.
I don't see how. The pump side is sealed by an o-ring which is pretty foolproof. I think it is likely that when the mechanic changed the pump, the loosening of the bolts allowed the seal formed by the front cover sealant to fail. Or possibly the front cover wasn't properly installed at some point.

If you are lucky, the sealant on the bolts will stop the external leak and there are no internal front cover coolant leaks. Keep a close eye on the oil for signs of coolant. If the leak persists, the only cure is to redo the front cover installation.

Dave
 

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Not sure about the 01 but my 05 required 2 smaller bolts than the oem bolts when installing the updated water pump. I’m sure using the longer bolts would do some damage.
 
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