Evening forum Had some issues with the engine running hot. Temp gauge always sticks dead on at 90 but recently been fluctuating up untill the first line then suddenly dropping to usual temp. Checked the bottom radiator hose and it's stone cold so figured thermostat has had it. Just replaced it one year ago but it had a new water pump and the coolant wasn't looking great when I checked. So, bought a new thermo and some G12 and did a full flush then added the coolant as per usual: back filled the top radiator hose, expansion tank with cap off and waited for it to get to running temp whilst massaging the hoses. Been at it for hours now but temp is still slightly above 90 and rides up until the first line. Bottom radiator hose is still stone cold also. I've run gotten absolutely all the air out of the system in anyway I can think of but the thermostat just doesn't seem to be allowing coolant to flow from the radiator (which is getting heat). Anyone have any ideas?
It's just weird that it's acting exactly the same as it was before I did the coolant flush/switched out the thermo. Did the oil today and it was looking good and have no symptoms of a head gasket failure. Will pop the thermo off then I guess and test it!
Must be the stat. I’ve always found the Mk2 cooling system really good in so far as I’ve never had an airlock. Always manages to purge itself really well. Check the stat and if you can be bothered run it without the stat as an extra check.
As above. Definitely run it without the stat to confirm the water pump is okay and moving the water. Get the hosepipe in and flush it both ways to ensure there is no other blockage.
You could test the original stat in a pan of boiling water. That would confirm the issue isn't with the 'stat Maybe cook a couple of boiled eggs with it so you aren't wasting energy #humour Are your hoses to/from the heater matrix getting warm? Something else to check the water pump is circulating the water. When I've refilled the coolant I've usually squeezed all the visible hoses to 'assist' the bleeding process.
Update: Tested the original stat and it was super grimy and sticking. Water pump is brand new last March and working fine. Cleaned up the stat and it opened bang on at 87/90. Did the same with the new one and it was also working as it should. So.. put the new stat back in and did the entire bleed process again. The issue I'm having is that the system wasn't getting hot enough to open the stat and bleed any air locks in the heater matrix. Revving it like a good un with hot air on max finally managed to get the stat to open and released a pitiful amount of bubbles (though at this point I'm happy to see any air released). Fan came on as it should. Top thin hose to expansion tank blowing bubbles and pushing coolant through so left the cap off and just let as much air out as possible whilst giving the local Thai massage parlour a run for their money on the hoses. Did this for nearly 2 hours... Got to the point where I'd have to turn the heat off just to let the temp get hot enough where the stat would open and then smash the heat on quickly and try to get air out. Mostly the coolant would just sit flush with the expansion tank cap and flow out without anymore air releasing. Otherwise, the bottom hose is getting hot as it should and if I close the cap temp would rise just above 90 and the fan comes on. Now, tell me I'm being pedantic, but I've just had a solid drive and the temp still sits at the top of the 90 line with the slider set to cold. If I whack the heat on max on full blast then it happily sits at 90 but with the heat off it's still sitting a tad too high. That's fine right now whilst the weather here in Norway is a balmy 4c but I'm concerned how summers going to be. Also, after the drive i parked up and revved her.. fan does comes on but once again it just brings the temp down to basically resting on the top of the 90 line. I'm guessing there is still a tiny amount of air still trapped in the system. I just hate having to constantly keep looking at the temp gauge and seeing it not right (it was always dead on 90 before I flushed it). So if anyone has any tips/tricks on venting that last bit of air I'm all ears, as I can't for the life of me figure out how to get that last bit if air out.
Heater on hot or cold makes no difference btw, there's no valve on the coolant. Sliding to hot just uncovers the heater matrix inside the heater box. What's your oil temp like? I often drill a 2.5.mm hole in a stat to help bleed coolant and to lower temps a little.
Full disclosure this is all happening on an Audi 80 B2... But it's pretty much the same engine as the 8v. It's strange that with the heater on max the temp lowers vs totally off it climbs. Oil temp is fine as is pressure. Was thinking about drilling a small hole in the stat, just annoying that before the flush it was fine and now not. Really feels like an air lock but I'm totally stumped on get that last bit out. If you drill a hole in the stat does it make a difference which side you drill. Stat sits vertical so wondering if it makes a big difference if you drill left, right, top or bottom. EDIT: On the other hand, the point of the stat is to basically give on demand heat... Something pretty essential in these parts. Surely if I put even a small hole it's just gonna take an ages to get heat into the cab or?
You will get heat in the car as soon as the coolant in the system has warmed-up. By the stat being closed the engine heats-up quicker in cold weather. Heat from the Heater has nothing to do with the stat being open. I suspect the reason for the temp dropping with the slider on hot and the blower on is because you are transferring the heat from the heater matrix into the car, hence dropping the temp of the coolant. The radiator and fan are there to stop the engine/coolant overheating. If you had no stat in and it's cold the radiator will stop the engine getting to operating temp quickly because it will cool the coolant regardless of the fan cutting in.
A couple of things. Firstly some people may know where 90 degrees on their temp gauge is but ours has no numbers at all, just marks so no idea where 90 degrees is. Secondly have you put an infrared temp gun on the pipes at all? How do you know what the actual temperature is? Our gauge only goes to the first quarter mark or just above but infrared temp gun confirms engine coolant is running at 90 degrees.
Thanks for the replies! I understand the purpose of the stat... The reason i was mentioning the heater was that I had to turn off the heat whilst bleeding to get enough heat into the system to get the stat to open. Did write this all in the OP but think wires have gotten crossed. As for the temp gauge, unless it's suddenly become faulty after the flush I have no reason to doubt it's accuracy. Of course it is possible that after the flush the gauge has suddenly become faulty, but I think it's much more likely that I have an air lock... Anyway, I'll break out the thermo gun tomorrow and check the pipes also just in case.
All I've ever done with my Mk2 16v is just fill it with coolant, it's basically self bleeding. I would imagine the 8v is the same. If coolant fan is cycling on/off and its not boiling the header tank I'd think it should be fine.
Yes I agree ,the 8V is no differant , always found they are self bleeding I usually run then with the cap off and watch for bubbles then when temp comes put the cap back on and job done @ that stage the system is free of air . What I found with my 89 8V GLI (jdm import) was a small amount of bubbles were always evident in the header tank ,being an import I suspected the head gasket as it is well known they don't do coolant changes much in Japan or very regular services for that matter ,issue continued for some time and slowly got worse which was then effecting the system by then . Had the system pressure tested and no indication of a failed head gasket , the mechanic mentioned other causes that I had already checked as ok he said that was strange , several weeks latter I noticed oil in the coolant then a week later the headgasket let go in a big way . My point is headgasket issues don't always crop up straight away, the bubbling in the header tank was the first "red light'' but it wasn't possible for me to attend to it as it was my only daily driver . When I changed the headgasket I found a rust track from coolant gallery to oil passage hence the oil in the header tank .
it could be the coolant simply isn't getting warm enough to open the stat, just need to leave it a bit longer. also as said systems with a coolant tank are self-bleeding anyway, if you check ElsaWin there is no bleeding procedure in a nutshell it just says 'fill it up to max, run engine to operating temp, top up if necessary' that being said I still do it, just because I always have
I did another flush and its still having the same issues. Checked the pipes/engine/coolant temp sender with a thermo gun and engine/pipes all running at 90c even though the gauge temp was saying we'll above 90c and triggering the fan to click on. Really odd, so had another dig around and found the spade connector of the sensor had snapped off... Weird thing is that even with no connection to the coolant temp sender the temp gauge works (somewhat). It almost reads right just running too hot. I would have thought that with no information coming in the temp gauge would have been at zero. So it's still getting some information from somewhere? Anyway, just bought a new coolant temp sender so will install and see if that happens.
hmm. if it was a MK1/2/3/etc golf a snapped wire would mean no gauge at all. audi can be funny things, or maybe its not the dash sensor wire you're looking at? either that or maybe the wire is shorting somewhere else, but somewhere dirty, so its not a nice clean short to earth but a slightly resistant short to earth, equalling about 90 degrees
How I miss my 8v Gti.... Yeah it's weird, the Haynes manual isn't that useful for my 86 pre face-lift model but the only suspect I have for the coolant temp sender is where I found the broken spade connector... Yet if I unplug it or not it makes no difference to the reading. Tested the switch and connector for continuity at 20k Ohms and it basically read back as nothing from both sides (0.02). So sounds like a electric gremlin. It's just so odd that the temperature doesn't spike straight away, but rises slowly as it should l, then fluctuatea between just above 90 and the line above it. Surely a bad earth wouldn't behave like that?
that spade connection on the side there is an oil pressure switch (as an admin I can see your deleted post) the coolant temp would usually be in the front or side coolant flange, yellow/red wire if it follows VW colour coding
Yes you're right! But god knows where the coolant sensor is then. It's not on the flange coming out of the side of the head, nor is it on the flange coming out the front.
