Help! My classic is overheating. I was driving back on open highway (no traffic) from having a bunch of stuff done, and glanced down at the digital LED readout. Holy fish--it read 230°! Just a few minutes before it had been 145, which made sense for the air temperature. This car has never gone above 190, even in summer, so something is clearly wrong. Question is, what? She has a 1275 cc engine, and had been running just fine before this, no complaints or noises.

Fortunately I was able to immediately shut down the engine and coast to the shoulder. I saw no fluids anywhere, including on the ground. When the engine was cool enough, I opened the radiator cap, and saw plenty of fresh antifreeze. It had just been replaced as part of the servicing I was coming home from. Also done at that time was a new fan belt, oil change, tune-up and a bunch of items unrelated to cooling, like rear brakes and a new steering rack, all done by a well-respected classic British car mechanic. A mechanic friend brought some water, on the theory that perhaps there was an air bubble in the system, but there was never a time with the engine running that the level went down enough (or bubbles showed) to suggest this was the cause.

By this time the engine was running in the normal 145 to 150 range. I got back on the highway and watched the gauge like a hawk. I could see it run around 150, spike up to about 175, then back down. I assume this was when the thermostat was opening and closing. I drove the remaining 7 miles to my neighborhood with it never getting above 191, and that level for only a few seconds before going down to about 170. Just short of my street it suddenly spiked again to 230, and I pulled over and shut the engine off. A short time later it was down in the normal range and I pulled into my garage.

So, that's the long story. Suggestions for troubleshooting? Does this sound like a thermostat? If not, what do you think I should check? What are the chances that it's the gauge, and how would I check that? Can't afford to just throw money at it, and I'm not sure I want to drive 65 miles back to the shop without knowing what's going on.

 

How long did you wait for the engine to become cool enough to remove the cap without scalding yourself? At 230F I think you'd have to wait some time.

Before you go much further I think you need to confirm the temperature via some other means.

One way is to use an infrared thermometer and take the temperature of various items/locations. The water pump housing/T-Stat housing is a good place.

If the T-Stat is suspect it has to be nearly closed. Thus the temperature there would be high while the temperature at the hot inlet at the radiator would be lower because the T-Stat would be preventing hot coolant from flowing to the radiator.

If the high temperature is for real and you confirm the hot coolant is *not* being routed to the radiator then the T-Stat is suspect #1.

 

If you were driving spiritedly it could be the fan belt slipping. If the timing was retarded the engine could get hot, but it would stay hot. Sticking thermostat maybe? What temp is it's rating? I like the idea of using an infrared thermometer to verify temps. You had several systems worked on, so a call to the shop seems in order.

 

I had a similar experience and it was a sticking therm'

I whacked mine with a screwdriver handle and it has never stuck again ... but it is a cheap thing to replace.

Harbor Freight has a couple of "non-contact thermometer" for between $20 and $30 .... I have one I use mostly to check temp's of the grates on my grill b4 I toss on meat ... it works fine. I've verified accuracy with a cooking thermometer and it is spot on ...

try running with the heater on full ....

if you don't know why I suggest this ..... maybe a classic ain't for you . . . . unless you have a deep pocket book

 

RockC--I'll try to borrow an infrared thermometer--seems like a good idea. I know lots of people who likely will have one.

BRGPA--not driving spiritedly, just cruising on open highway at about 55.

Capt_bj--yes, I know why you suggest it, but I didn't think of it at the time. We've lived with a classic for 51 years, but it's an aircooled Porsche, so not quite the same! Pockets are sufficient, but don't want to waste money.