My temp gauge keeps teeter totting on the highway I can not use the ac at all now what would cause this to go real high then back down over and over?

Asked by May 19, 2016 at 11:14 PM about the 2004 Subaru Legacy L 35th Anniversary Edition Wagon

Question type: Maintenance & Repair

I have a Subaru Legacy where when I am
on the highway the temp gauge goes real
high and the. Back. Down to normal over
and over and I sure can't use the ac!!

7 Answers

5,605

I wouldn't drive it until you get it fixed. Whether it's a thermostat, water pump, head gasket, leak, or other issue.. just don't drive it and warp the heads (if they aren't already?).. I'm guessing head gasket since the load from the AC is making it worse? Try to get some "ball park" estimates from local places and get a feel for who has the most realistic prices, explanations, best bang for buck. maybe even google maps search (and skim reviews) for mechanics. HTH

5,605

Also read this: https://allwheeldriveauto.com/subaru-head-gaskets- problems-explained-part-ii/

2,800

Search the forum, as I've addressed this in length several times. Quickly: OE t-stats and water pumps are always fine, so ignore unless someone put in an aftermarket one on you; check rad for exterior front surface debris (leaves, mud, dirt); back-flush heater hoses (under windshield). Be sure to purge air fully. Still overheat under load? Sniff expansion tank for HC, indicating exhaust gas percolation. If so, you need HGs ($1600), suggestiing tossing this baker's dozen years Subie. But do the simple stuff first (but it ain't a t-stat nor water pump).

1 out of 1 people think this is helpful.
5,605

what is HC? Hydrocarbons?

2,800

Yup. First gases will bubble up under light throttle; eventually full- time at hot idle, with even violent explosions when revved up. One of the few times I wear eye protection.

55

also your gauge might be going out

2,800

In my 30yrs exp servicing thousands of Subarus I've NEVER seen a faulty temp gauge.

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