Which gauge do i trust?

Griff71 · Posted: Sun Apr 24, 2011 10:20 pm Post subject: Which gauge do i trust?

Ok i have been having overheating issues again recently mainly a stock vw gauge telling me i am running way too hot. Also on one occasion i have thrown a hose again and lost all coolant. As some of you may know from my last posts i have got so pissed with overheating issues i had chosen to ignore it and continue as if all was well. Figured if engine cooked itself i would have to get another and this irritating issue would be over.

Well i am still clocking up miles with the VW guage in the red flashing like mother******. I have not heard the fan come on in ages yet all checks suggest it's ok. (I can check this via the Subaru connections which will run through fuel pump and cooling fan in sequence).

The other day i thought enough is enough so did a combustion check confirming no head gasket failure. Compression test is perfect all equal psi and no loss of power. So I finally delved into my wallet and found some pennies to purchase a digital gauge and sender.

Now the stock VW guage will be flashing and needle will be way over to the right>HOT, within 10 minutes of driving. However the digital gauge will sit at 76-78oC whilst driving 60-70mph. In traffic or at idle it will sit at 88oC rising to 92oC with the fan kicking in instantly bringing the temp down to 85oC. Reading up these are the temperatures suggested for normal running temp.

So despite all seeming well it appears my vw gauge has packed up and i in fact have no cooling issues. However this does not explain pressure build up and throwing a pipe. Which to me suggests boiling due to HG failure, maybe a blockage. Have checked again and again for leaks but yet to find any.

Any advice or ideas would be appreciated. Any one else experienced similar?
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89 Crew Cab (Subaru 2.5na)
71 Drag Bug (1955cc dual 40s)
65 Ragtop Bug (low & stock)

james72 · Posted: Sun Apr 24, 2011 11:22 pm Post subject:

To get the stock VW temp gauge to read correctly from the subaru loom a 27ohm resister needs to be wired in line, or the temp gauge reads high.

Those digital reading seem spot on mate, pressure build up could be a dodgy header tank cap, if your sure the HG is OK
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1989 VW Magnum Multivan EZ30

rjes · Posted: Mon Apr 25, 2011 4:05 pm Post subject:

Definitely check the header tank cap vents when it really does get hot. If it's not venting you could end up replacing the water pump, radiator and heater matrix after they all fail as a result (direct or indirect) of the pressure being too high. This is exactly what happened to my mate's conversion not long after installing it. The pump, matrix and rad cost £200 ish before finding the real cause - the new cap on the new header tank he'd bought was stuck closed. One second hand one (which he had lying around in his garage the whole time) later, and he's used if for about another 3 years now with no cooling system problems.
The caps are not very reliable. The two way valves inside them often fail either permanantly closed or permanantly open. I've seen more than one new one which doesn't work.
Griff - If I remember right, I did your harness work? If so, unless either you've removed it or I somehow forgot to fit it, your harness will already have the resistor.
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Regards,

Richard,

R J Engineered Solutions
Quality Subaru Powered VW Components
www.rjes.com

Griff71 · Posted: Mon Apr 25, 2011 8:57 pm Post subject:

Yes Rich you did do my harness so i most likely have a resistor still fitted. If i remember rightly this fitted at the radiator and had to be taped up. Remember doing it and don't think i have looked at it since. I am just wondering whether my mate has changed it when i had electrical issues.

As for caps i have so many now the one on the van was off a mates that had no issues.

Confident the temp is ok now as fan comes on at 92oC and will sit at 76oC all day long whilst driving. Have been out and about and had the most fun i have had since i first fitted the motor nearly 3 years ago. Chasing bikes is such a buzz especially when they ask what the hell you got in there? Even had a guy on a fireblade say 'sweet ride mate' today.

Hopefully i wont have a pipe come off again though. Do wonder whether it did just get overly hot in traffic.
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89 Crew Cab (Subaru 2.5na)
71 Drag Bug (1955cc dual 40s)
65 Ragtop Bug (low & stock)