GTX running hot

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BlackGT
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GTX running hot

Post by BlackGT » Wed Feb 13, 2019 11:11 pm

I've got an '87 GTX which has recently started running hot - previously at motorway speeds the temp gauge would sit just below halfway, it's now just over halfway, although I can get it back to halfway by running the heater on hot. Looking at the oil temp, it's around 100 degrees C at speed, rising to around 110 degrees C when stopped which seems high.

Ever since I've had the car, it's had a quirk that when stopped the gauge rises to a bit over halfway, then the fan comes on and it drops to just below halfway. I'm assuming that the hot running at speed is a sign of this problem getting worse...

I've changed the radiator and thermostat and flushed through the cooling system with a hose which hasn't make a lot of difference. After the last run, the gauge was over half and the heater was roasting hot, but I felt the radiator bottom hose and it just was warm, and the fan didn't come on. I'm thinking the water pump is the most likely culprit - I had a look at the impeller when the thermostat was out and it looked ok, but I'm wondering now if the impeller is slipping on the shaft.

Has anyone had this problem in the past / have any advice?



mark1gls
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Re: GTX running hot

Post by mark1gls » Wed Feb 13, 2019 11:33 pm

1st off I would check the spade connector onto the temperature sensor, the wires can fray over time and It could be hanging on by a few threads of wire or the spade connector get lose, you can squeeze it a little to make it a tighter fit.

Normal running is 1/2 around the rd LED light then when it gets to 3/4 the fan kicks in and it cools to about 1/2 way.

How old is the engine oil, older oil will run hotter than fresh oil., 10,000 or 12 months between changes.

What coolant did you use and was it ready mixed or concentrated?

Normal for the bottom hose to be cold after a run when the weather outside I’d colder as the thermostat opens when hot and closes when coolant drops cooler. During 1 winter my thermostat stuck open coolant would not get above 1/4 and my oil (water cooled oil cooler) would not get above 80 degrees when driving/moving at 50/60 mph and once stopped in traffic it would get to then normal 90ish degrees

The water pump runs off the alternator belt, check it’s at the right tension.

Check for any air lock, with a cold engine make sure the heater is set to hot, remove the expansion tank cap and run the engine, you should see a small jet of water from the thinner hose from the rad and if you rev the car the flow should increase. Let the car idle for about 5 mins with the cap off and squeeze the main hoses to check the amount of water in the tank moves up and down and burb the coolant system , refit cap and the pressure in the hoses should increase over the next few mins.
Turn off the engine once the fan has kicked in and stopped then let it cool down for a few hours or over night and top up coolant if needed.


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mr.brown
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Re: GTX running hot

Post by mr.brown » Thu Feb 14, 2019 10:56 am

Same problem on a GT and I flushed and changed everything - pump, stat, rad, heater matrix and it still did it. Upgraded to the GTX fan and changed temp sender and it still did it. Finally bought an IR thermometer "gun" and found it wasn't overheating after all - it was the gauge.

With respect to the "quirk" - when driving you are getting cool air flow. When stopped, this flow stops and under-bonnet temps rise initially. As the fan works independently of the ignition, it's natural that it will kick in.



BlackGT
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Re: GTX running hot

Post by BlackGT » Thu Feb 14, 2019 2:45 pm

Thanks for the replies and advice - much appreciated! To answer some of the points:

I changed the oil a couple of weeks ago

I'm using concentrated OAT coolant, 50/50 mixed with water (I know it's not the recommended type, but the car had been swapped to OAT when I bought it and it seems ok)

I've checked the alternator belt, it's fairly new and not slipping

I'm fairly sure it's not an air lock causing the problem as it was occurring before I changed the coolant, and prior to that the system hadn't been touched for 2 years. I bled the air using a similar method to what you described, sounds like it's worth checking again though. I'll also check the coolant sensor wires (do you mean the sensor on top of the expansion tank?)

That's interesting about about similar symptoms caused by a bad gauge - the thing that makes me think this isn't the case it that the oil temperature displayed by the MFA, which is an independent measurement, also gets too high.

With the "quirk", although I agree with your explanation, but if the coolant is circulating properly shouldn't the fan temperature. sensor switch on the fan as soon at the temp begins to rise, meaning that the gauge should hardly change? I have a mk3 Golf with what seems like an identical cooling system setup, and the gauge stays bang on the centre at all times once it's warmed up. The oil temp reported by the Golf is also a constant 86 degrees.



mark1gls
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Re: GTX running hot

Post by mark1gls » Thu Feb 14, 2019 4:08 pm

The coolant temp sensor is one on the front of the head, big hose to top of the radiator, check that connection and the oil temp sensor on top of the oil filter. The sensor on top of the expansion tank is low level coolant and it's triggers/works the red LED in the temp gauge.

The temp needle should rise once stopped in traffic, it will go up to 3/4 before the fan kicks in then back down to 1/2 way, just worry if it goes above the top line and near the red.

Are you missing any of the radiator cards as that can make a difference to air flow into the radiator as well.

My oil is 90 degrees when moving at national speed limits come winter or summer, stuck in traffic with coolant fan coming on and off in the summer 100-110 degrees. Hammering it it's got to 115 degrees and that's as high as I've seen it.

I've been driving my mk1 Golf as a daily for over 20 years and even driven across Europe on some very hot summers days, to the cold winters we do occasionally get here when my outside temperature gauge is saying -8 degrees.

Briano1234 on the Mk1 golf forum has posted lots of fixes etc, the Mk1 golf cabrio is the same running gear etc as Mk2 Scirocco.

have a look through here for fixes and how to get a better earth and concoctions into the instrument display.

https://vwgolfmk1.org.uk/forum/index.ph ... -of-things

https://volkswagenownersclub.com/vw/sho ... Temp-Gauge


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blakey
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Re: GTX running hot

Post by blakey » Thu Feb 14, 2019 5:32 pm

I previously had an '88 GTX which did exactly the same, after replacing water pump, thermostat, expansion tank & cap and radiator with no improvement, I concluded that it was likely to be the head gasket furred up and expanded around the cooling passageways between the head and block. Unfortunately, I later sold the car for other reasons, so never got to resolve the issue. It never overheated even on the hottest days.

Conversely, I now own an '89 Scala injection, which runs too cool, low coolant and oil temps, even with previous owner fitting a non injection radiator. I'll be changing thermostat soon in an effort to resolve it.


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mark1gls
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Re: GTX running hot

Post by mark1gls » Thu Feb 14, 2019 7:56 pm

Another idea...

What fuel are you using, Super or normal unleaded?

Has the timing been adjusted to the fuel you are using as if the timing is out the engine will run hot....


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BlackGT
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Re: GTX running hot

Post by BlackGT » Sat Mar 02, 2019 10:06 pm

Thanks for the suggestions - the links look very useful too! I'm not missing any radiator cards. I'm using normal unleaded petrol, but the fact that it was fine for almost 2 years of my ownership rules out the timing issue I think.

The old coolant had a tinge of brown, and I flushed the cooling system out with a hose when I changed the radiator. I've just removed the water pump and the new coolant had gone brown, and there is a thin layer of rusty deposit on the water pump and in the pipes - thinking I need something stronger than water to flush it out - does anyone know good products for this?

The water pump housing has score marks around the impeller - I'm not sure if this explains my problem, but looks like it was due for replacement anyway! New one arriving next week :)



mark1gls
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Re: GTX running hot

Post by mark1gls » Sun Mar 03, 2019 10:47 pm

Good guide here on flushing out the system, should get rid of anything in the system.

Ignore the power streering and it’s a golf cabriolet as the basic set up is the same as Scirocco.

https://volkswagenownersclub.com/vw/sho ... r-radiator


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james butler
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Re: GTX running hot

Post by james butler » Fri Mar 08, 2019 10:35 pm

the fact your oil and coolant is high makes me think engine temp is genuinly high
the temp is regulated by thermostat s my first port of call would be to remove it and test it in hot water to see at what temp it opens and how much.
i have tested numerous new stats and found some that open early, some that open late and others that were dead out if the box!
so i would test it and see.
i need to fit a lower temp stat in my rocco to overcome a overheating issue as all 91 degree stats i have so far all open late and not enough.
bad fuel can also effect it like has been said timing and mixture can be affected if you have a bad batch of fuel making it run hotter than normal.


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BlackGT
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Re: GTX running hot

Post by BlackGT » Thu May 16, 2019 10:28 pm

Thanks for all the advice - fitted the new water pump and took a lot of care bleeding it properly ( thanks mark1gls) and all good. Temperature now between 88 and 91 when moving, when stopped it rises to the mid 90s before the fan comes on. Interestingly, turning on the headlights causes the temperature guage to rise a small amount and the oil temperature to immediately jump 5 degrees... Guessing an earthing problem or something.



mark1gls
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Re: GTX running hot

Post by mark1gls » Thu May 16, 2019 11:43 pm

Good the hear it’s running cooler now.
Does sound like an earth issue, check the brown earth wire in the engine bay on the back of the rocker cover, there should be a thicker wire from the coil bracket and another thinner wire attached to the cam cover, the thinner wire earths the instrument cluster and can course all sorts of problems with the instruments, when mine broke if I switched the headlights on the Rev counter would die....

Another mod to help is a headlight relay kit if you don’t have one as it stops all the current running through the light switch then onto the headlights, it reduces voltage loss to the headlights and stops the headlight switch melting over time which can happen.

Something like this or you can make your own loom.
https://www.ebay.co.uk/itm/vw-golf-mk1- ... SwaNBUeNlq


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BlackGT
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Re: GTX running hot

Post by BlackGT » Tue May 28, 2019 1:14 pm

Thanks, will check the wire! Sounds good, I don't have the headlight mod so will look into that too.