# overheating after thermo install



## b4drivin (Jan 19, 2009)

this has been asked many times before but i was wondering something. i have a 87 golf 1.8l 8v and decided to replace the thermo today. at the time i bought the car the previous owner said that it was stuck open. with the temps dropping outside i wanted to replace the open one foe one that actually works. any how did the install today and found that there was no thermo, which kinda made me pissed. so i installed the new one, added fluid, started the car up, temp gauge came up fine but then it started overheating. pulled off, shut the car off, popped the hood, checked upper and lower hoses. upper one hot, bottom cold. drifted it home. Here is the question, i read up on about drilling the thermo before installing to allow coolant to enter the other side. is there another possible way to fix problem without draining coolant, uninstalling, drilling, then re installing? any help would be greatly appreciated.... thanks


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## ps2375 (Aug 13, 2003)

Fill the motor with the upper rad hose.


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## ziddey (Apr 16, 2006)

the way I always do it is leave the cap off. massage the hoses. put cap on very loosely and drive like that for a day. top off coolant, tighten cap.

can the tstat be installed backwards for these cars? known good tstat? how overheated did it get? did your heat work?


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## b4drivin (Jan 19, 2009)

*going to try*

thanks on the feedback, going to try both this evening once i get off work. hopin it solves the problem...


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## b4drivin (Jan 19, 2009)

*any other suggestions*

yesterday i filled upper radiator hose, squeezed hoses, started the car and ran it with the cap off. nothing, still overheated. pulled it back in the shop, lifted it, took out thermostat and drilled an 1/8 inch hole in it, put it back together, started it up. temp gauge went up but nothing like it was at least until i drove it. temp gauge climbed and climbed. any other suggestions other than the water pump being bad?


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## b4drivin (Jan 19, 2009)

*clog*

is it possible for the radiator to be clogged... thought about taking the hoses off it and flushing it.


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## b4drivin (Jan 19, 2009)

*update*

well i took off the hoses to the rad. ran water through it and no clog. decided to just take out the thermo.. refilled, started up and took it home with no overheating problems. would really like to figure out what the problem is so i could have some heat for the winter. any suggestions from anyone would be appreciated greatly.

really thought i would have some replies to help out... thought this was the ultimate vdub site...


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## ps2375 (Aug 13, 2003)

Two things:

1. Is the thermostat installed correctly?

2. Have you checked the water pump or replaced the water pump?


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## Fat Rabbit (Nov 18, 2001)

I'd have to second the above post. Was the thermostat installed correctly? The longer spring end of the thermostat installs toward the engine up into the water pump housing.

The thermostat you installed may also be bad. I have found them bad new out of the box. Although I usually just replace thermostats you can test the thermostat by boiling it in a pot of water to see if it moves enough. At a minimum you need just over 1/4" difference between hot and cold lengths.

Sometimes the impeller on the water pump breaks free from the pump shaft causing no or poor pump operation. So that is also a possibility if the thermostat checks out OK. 

I see that it has also been suggested that you fill the radiator through the upper radiator hose. I fill both the block and the radiator through the upper hose. FR


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## b4drivin (Jan 19, 2009)

*update*

thermostat was installed correctly with spring up toward engine. water pump propellar isnt broken free, i had a friend turn the engine over while i watched the propellar from underneath... filled the radiator and block from the upper hose... and still it overheats.... is it possible that there is switch, gauge or something on that side thats bad... i also did check the thermo prior to installing by boiling it in water....


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## dkfackler (Feb 8, 2010)

Do you have a coolant reservoir? If so, be sure the small hose connected to the upper part of the reservoir is clear. It should dribble a stream at idle; more as RPM increases. There may be a factory restrictor in the line and if it gets plugged, you get an air bubble which can't be bled out and you will overheat.

Remove that small line and blow compressed air through it. I suppose it could be gooked up at the other end, so trace it and be sure the whole line is clear.


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## ps2375 (Aug 13, 2003)

Is the motor actually overheating, or are you just going by what the gauge says? I have seen those read incorrectly. And, just watching the pump turn with no water (load) is not much of a check. For the price and all the trouble you are having, I would put a new pump in to be sure.


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## b4drivin (Jan 19, 2009)

*already did*

when i flushed the system i did shoot air through the small hose... my temp reads hot cause the car is actually overheating... how can i tell, well lets see the oil gauge comes on, notifying me that the oil is low, in which i can only determine thats its getting so hot thats its thinning out the oil so much to have it not register...


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## ziddey (Apr 16, 2006)

exhaust gases in the cooling system? head gasket?


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## b4drivin (Jan 19, 2009)

*compression test*

what ways are there to do a compression test to see if it is a head gasket? from the simplest to hardest.


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## ziddey (Apr 16, 2006)

compression test won't show much. check if you've got HC in your coolant


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## dkfackler (Feb 8, 2010)

b4drivin said:


> what ways are there to do a compression test to see if it is a head gasket? from the simplest to hardest.


Test compression-- if you have 2 adjacent cylinders with very low(say 40 PSI lower than the others), it's pretty conclusive.

Get the tester that screws into the plug hole-- the tester that you hold in by hand won't work nearly as well. Pull the fuel pump fuse or take the harness plug off the ignition distributor if you have one. Hold the throttle open as wide as possible and crank the engine until the gauge is at its highest reading. Write it down. Repeat for remaining cylinders. compare numbers. Repeat test.


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## b4drivin (Jan 19, 2009)

*HC*

whats HC?


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## dkfackler (Feb 8, 2010)

b4drivin said:


> whats HC?


HydroCarbons


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## Twinrocco's (Jan 8, 2009)

H/C Bentley says overheating can be caused by hot combustion gasses leak into the colling system. Iam having the same problem. the car had a growling noise at the frount of the engine.I replaced the pump. Now its over heating. I think I dont have the colling system filled correctly. The fluid not circulating .Iam letting the car sit over night an going to fill the radiator from the top . hope to get it flowing. Let us know how you make out. If I dont have any luck Iam going to need help as well.


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## b4drivin (Jan 19, 2009)

*just cant comprehend*

i filled from the upper rad. hose, to it and the block. still overheated. havent had a problem since taking the thermo back out and leaving it out. now just dont have heat for winter time unless problem can be sorted. the only other thing i thought of for the winter time was to cut a piece of 20 gauge and block off some of the rad.


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## grumpylamp (Nov 29, 2010)

*same problem and solution...*

just registered on the site to solve my same problem

My 87 cabby has run 'hot' for the last 2 years since I got it.... dash gauge was near the far right line... small lower gauge read about 1/3 up....

finally checked to find the upper hose very hot and lower hose cool

took out the thermo and the dash gauge never goes above !/2 and usually hovers near the first mark on the left... lower gauge is also a bit cooler

put a new thermo in and upper gauge goes up to near the top, perhaps not at far as it used to... 

ran water through the radiator and with the car running ran water through the upper intake to the radiator which came out the upper hose ( I thought this would show that the water pump worked and the radiator was not clogged).

Northern california doesn't need a heated car in winter, but I'd still like to know what is up... will drilling out the thermo solve this issue?

just sharing and wondering


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## b4drivin (Jan 19, 2009)

as far as drilling out your thermo some old timers around my shop said that they used to that to prevent air lock... which happens when replacing thermo and filling back up with coolant somewhere along the line it doesnt fill properly and an air bubble can form causing the flow to be rejected. in turn over heating the car... not sure 100% that this method even works, i tried and failed but others might have luck...


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## TheBurninator (Jan 7, 2009)

You guys aren't filling the system correctly. You need to burp it.

1) Fill the motor the best you can from the upper radiator hose
2) Fill the radiator as best you can also
3) Fill the overflow tank, leave the cap off
4) Start the car and let it come up to temperature
5) Fill the overflow tank as needed
6) Make sure your fans are coming on (sure sign that the thermostat is opening and working)
7) When the overflow doesn't take any more fluid then you have a properly burped coolant system

This usually takes about 15-20 minutes depending on how cold or warm it is outside. Rev the motor a bit while you do it to work the bubbles out of the system and out of the heater core.


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## ragnar's vw (Oct 3, 2004)

is the left side of the radiator getting hot (where the fan temp switch is)? if it is getting hot and the lower hose is getting hot, and you have coolant flowing throught the small hose into the expansion tank you have good water flow. if the one side of the rad. is cool the rad. is plugged or you have an air pocket. the fan should come on when the entire radiator is hot. if no hot water gets to the switch the fans will never come on. i had a blocked bleed line to the exapnsion tank and it did the same thing. it acts like a plugged rad. but it just wouldn't let the air bleed out of the system.


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## b4drivin (Jan 19, 2009)

ill try the new suggestions, but as far as the fans coming on the previous owner said that due to a battery going bad, melting the wires to the fan switch as well as others theres a toggle to run those now once i see that they need to be kicked on from inside the cab. burping the system ill start with following your steps then the whole rad. thing next.


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## scirocco16v (May 17, 2000)

See above about "air lock" this is very common on VW 4 cylinder engines. In the shop I work in we always apply 25"hg of vacuum to the system before filling it to prevent air bubbles. There's an awesome tool that uses shop air to do this. If you do get an air bubble in the system it can prevent coolant from making it to the T-stat and thus it will not open and cause overheating.


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## r1racing707 (Dec 24, 2010)

*???*

In the shop I work in we always apply 25"hg of vacuum to the system... what is 25'hg


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## VeeDoubleYouGuy (Nov 4, 2003)

definitely air lock. keep burping the system until you get circulation. all symptoms point to air lock let it get hot then cold then hot and squeeze hoses basically anything to make pressure in the system fluctuate and dont forget to run the heater core on high and rev the engine. you wanna get air from the highest point in the system so maybe put the car on a ramp etc....?


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## r1racing707 (Dec 24, 2010)

im having the exact same problem. cold lower hose hot upper. new ater pump and new thermostat. any ideas?


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## TheBurninator (Jan 7, 2009)

VeeDoubleYouGuy said:


> definitely air lock. keep burping the system until you get circulation. all symptoms point to air lock let it get hot then cold then hot and squeeze hoses basically anything to make pressure in the system fluctuate and dont forget to run the heater core on high and rev the engine. you wanna get air from the highest point in the system so maybe put the car on a ramp etc....?


The highest point is the overflow tank anyways. No need to put the car on ramps.



r1racing707 said:


> im having the exact same problem. cold lower hose hot upper. new ater pump and new thermostat. any ideas?


Did you check the thermostat before putting it in?


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## r1racing707 (Dec 24, 2010)

it was a brand new thermostat. is it possible to be in backwards?


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## scirocco16v (May 17, 2000)

Vacuum in automotive scales is measured in inches of mercury. "=inches Hg=mercury. For example, when you put a vacuum gauge on a decent running car's intake manifold, you should see 18-22"Hg.


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