Could anyone tell me the basic steps on how and where to replace the thermostat on a '79. Thanks for your help!

 

If the housing is set up like my 87-

Remove reservoir cap and rrain coolant from both radiator (blue plug on pasenger side) and block (two 13 mm bolts in the block just forward of the exhaust collector).

Remove the upper hose and the 2 allen head bolts which hold the tstat housing to the coolant cross over pipe.

Remove old tstat and oring [optional - check condition of seal ring installed in the cross over pipe - applicable to 87 models, don't know about the earlier years]. Check for cleanliness. Install new tstat (vent hole up) and oring (remember - the oring must be installed in such a manner that the oring is between the tstat and the tstat housing that you removed earlier). Also, be sure that the oring is the larger size (if you order from one of the big three - youl'll get the right one). Install the tstat housing to the cross over pipe and tighten the allen head bolts. Connect upper house and refill coolant system with the correct aluminum friendly anti-freeze and distilled water mixture.

Be sure to purge the system of air by squeezing the hoses periodically after you've started the car and let it warm up (BE CAREFUL - hot surfaces and moving belts/fans/etc.).

hth-

 

On the earlier models it is actually easier than the method Jay describes.

Drain about a gallon of coolant from the radiator - any more and you might as well do a full drain and recharge. Save that coolant for reuse (assuming it's in good condition). Otherwise, you may want to do a system drain and refill as Jay describes above.

Place an absorbent towel under the housing/hose end to catch the coolant that will dribble out - do not allow coolant to run down the front of the engine - it could contaminate the timing belt.

Remove the large radiator hose coming off the front center of the engine. The thermostat is located within this housing. Using a 12mm socket wrench with extender, remove the two bolts that secure the front portion of the thermostat housing. Be careful with the wiring harness that runs across the engine here to prevent damaging those old wires.

Gently remove the front housing section. Some additional coolant will seep out. The back side of the thermostat will now be exposed.

Carefully pull the thermostat out of the housing using pliers. Note how the thermostat is oriented for proper installation of the replacement.

There is a black gasket on the front side of the thermostat that should be replaced. This is a flat gasket - not an O-ring type. Be sure to specify the type of gasket you need. Most suppliers will assume it is the O-ring type.

To verify that the thermostat is your problem, I recommend testing it in a pan of water on the stove. Using a thermometer, heat the water to the rated thermostat opening temp. If the thermostat does not open at the rated temperature, it is indeed defective.

Clean up all the thermostat housing mating surfaces, apply grease to the threads of the retainer bolts and reinstall, being carefull not to overtorque those bolts.

Replace the coolant you removed.

 

thanks Randy for the detailed information.

 

Checkmate,
Just did mine on the side of the road,
at SITO.
WE used a 10 mm on those 2 gooseneck bolts - I would recommend a dab of anti-sieze when you reinstall them. If you leave the gooseneck thermostat housing on the hose you can simply hook it on the crossbrace, out of the way, (thanks Dave) while you are tinkering... if it's been in awhile tap on it lightly, and I believe Dave stuck a pair of neelenose pliers or a wrench thru the two support bridges -on the thermostat- and she came out after a few tugs.
If you have a small magnet to put on the socket or a dab of silicone to put in the wrench you shouldn't lose the bolt or washer into the intake valley of lost things. The bolt on the lower/passanger side has a wire bundle and I think a vacuum line in front of it. you should still be able to reach the bolt - don't crush either. Everything else is same as above.
HTH
John S. and - assistant roadside wrench - Dave. <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

 

Great tip! These should all be added to 928 FAQ section.