overheating issue

Richard Perrine

LVC Member
Oct 3, 2014
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Have a '95 MK VIII just obtained. noticed new radiator was installed. has overheating issues. boiling over at the resevoir.

replaced thermostat, refilled system through the petcock above water pump, no change, still getting hot after a few mins.

completely removed the thermostat adn o-ring and used some gasket material to seal the motor. re-filled entire system with plain water for heating and leak test before i put in more coolant. STILL overheats within a few minutes. electric fan does kick on. now im scratching my head. system appears to be circulating.

car is sitting out there now, hotter than a $2 pistol and boiling over at the resevoir (cap will have to be replaced im sure). only thing i can think of at this point is cloggged radiator. could it be anything else while im waiting for it to cool back down?
Open the drain on the bottom of the radiator. Stick a hose in the overflow and let it or pour through the radiator....or lack there of...to find if it's clogged.
flushed radiator. clean water pushing through no problem.

filled with straight water again, started boiling over and temp guage pegged after a 3 mile drive, bypassing the radiator cap

no water in the oil, no white exhaust smoke, not losing water.

is it possible its the water pump even though the belt is driving it? could the internal impellers be seized and still turn the outer portion? there is a squeeling noise that appears to be coming from either the WP pulley, or the tensioner, or idler pulley,, cant lock down the location.
Pull the belt off and give the water pump a spin with your hand. It's possible the pump's bearing close to going out and is heavily resistant. If not, pull it out and see what it looks like. Water pumps are very easy to do on this car, just make sure you remove the right bolts holding it to the block. There are a couple that are right next to other bolts that have nothing to do with the pump. It's theoretically possible something happened to the impeller and it isn't moving much antifreeze around. A new one only costs ~35 dollars.
I don't know of any "petcock" above the pump. The cap on top of the crossover pipe is where the system should be filled. When I did my 95's fill, it took about 15-20 min to get all the air out. You can see the flow looking into the opening. The level goes up and down. When it goes down add a little, and wait. When it stays up you have it filled. Your temp gage is most likely show hot. Could be lots of air in the system, making lots of steam.
crossover pipe.jpgHere's a pic of the pipe and fill plug.

crossover pipe.jpg
the fill plug is what I was erroneously referring to as the"upper petcock". Air was my concern too. i removed the upper radiator hose and filled the radiator directly from there, put it back on, then contnued filling through the plug hole, then topped off the resevoir tank. granted this is straight water and i understand it will boil,, but it doesnt seem to be circulating. the cap is defintiely bad now too. going out to check the water pimp to see if turns free or if i can feel anything "off" in it.
Theoretically you should be having better luck with pure water cooling than 50/50 antifreeze, not worse. Pure water has a higher specific heat capacity than 50/50 antifreeze, its ability to carry away heat.
i removed the upper radiator hose and filled the radiator directly from there, put it back on, then continued filling through the plug hole, then topped off the reservoir tank.

The reservoir tank should be filled first, then put its cap on. You shouldn't have to add any more coolant to the reservoir tank after you have it at correct level.

This link should be referenced for the correct coolant burping procedure. http://markviii.org/psjs_faqs/09297748.shtml#10241949

There is also good info on this procedure here. http://www.reischeperformance.com/refill.html
the old water pump free spun when removed, but i changed it anyways. refilled with clean water. ran it at idle for about half an hour, regularly "burping the system". temp climbed to 3/4 mark.

fan kicks on at about 2/3 mark. drove the car 5 miles, never went above 3/4 mark. steam still bypassing the radiator cap, must be exceeding the 16lb limit.

tomorrow going to drain, reinstall thermostat, refill with 50/50 coolant, burp in idle, and see how we do. might pick up a fan from the scrap yard.
If it seems to run properly after that, but still reads hotter then mid point....word to the wise....change the temp sending sensor. That ended up being my problem after chasing everything else lol.
Has the message center ever started flashing and beeping about engine temperature being out of range, it should say 'Check Engine Temp' and beep like if your trunk was open? If not your instrument panel gauge may simply be incorrect.
Has the message center ever started flashing and beeping about engine temperature being out of range, it should say 'Check Engine Temp' and beep like if your trunk was open? If not your instrument panel gauge may simply be incorrect.

the messge center would only flash CHECK ENGINE TEMP, once the temp was pegged. mostly it stays stuck on DOOR AJAR,, and i did everything i could find to get rid of that message. is also displaying the AIR RIDE message but i know thew air ride system is bad.

this is just a $300 beater car
Spray a bunch of wd40 or something like it into the latch assy on BOTH doors. This has solved door ajar message for lots of us. Don't be cheap spray,spray, spray.
is it the actual latch or the plunger button near the door hinges? the plunger buttons have been sprayed with PB Blaster, and unscrewed a whole turn. for some reason interior lights are staying on (the door panel lights and the ones under the dash to illuminate the floor). ive also sprayed the latches and opened and closed the doors a bunch of times. not helping.
UPDATE: replaced water pump, 2nd thermostat, already has a new radiator, filled with 50/50 coolant, burped system.

ran in idle for about 10 mins, car came up to middle mark on needle guage, fan didnt kick on. drove the car 1 mile and temp guage pegged, fan worked, and message display for check engine temp came on. checked resevoir, not boiling or excessively hot. doesnt smell hot

suspecting both temp sensors are bad (1 controls needle and fan and the other the message display AFAIK).
If it was me I would be doing a hydrocarbon test. If you rev the throttle do you get bubbling in the coolant reservoir?
Did you crank the heat on high when you were refilling? You can leave the cross over pipe cap off while idling to let any air escape and also see if you have flow. Are you sure that the thermostat was installed properly?
thermostat installed properly, the pointed end down, since its the only way it goes in to the housing. coolant pumps out of the crossover pipe when the plug is removed. drove car about 4 miles, and temp guage was showing normal. got behind a slow moving car and the temp guage started to go up to max. car doesnt smell hot but the overflow resevoir was bypassing a little coolant even thuogh a new cap. fan still doesnt kick on til temp guage shows 3/4 mark
unplug the 2 wire temp sendor on the crossover, this will force the fan to full on, does it stop the overheating?
ok, refilled the coolant,, and am running it for only about 5 mins. i revved it up and it defintely does gurgle and overflow the resevoir.

not circulating? another bad thermostat?
If it's overflowing the reservoir then your thermostat is not working properly. Defective thermostats are pretty common.

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