1991, 240, the temp guage reads eratically high, just below red. It will be about mid range idling, then go up if i put it in drive, but back down towards upper - mid range driving. The top and bottom hoses are hot, maybe about 180 F. Sides of the radiator are hot, but the finned area itself seems cool. I removed the coolant resevoir cap, and some coolant spewed out, but was relatively cool.

Shouldn't that coolant (in the resevoir) be more or less as hot as the radiator hoses? Is it spewing out due to pressure from a bad head gasket? There is no oil in the coolant or oil/water emulsion sludge under the oil cap. Removing the oil cap will show a little smoke in the cam area, it seems kind of hot.

I just bought the car, according to repair records, the thermostat was changed recently.

Any ideas? How does one find and bypass the temp guage compensation circuit to eliminate that as a possible culprit?

All advice appreciated ! Happy turkish day.

 

A really good pictorial on the bypass of the temp. comp board.

http://cleanflametrap.com/tempFaker.html


Good luck

 

This could be a water pump problem, but don't discount the radiator or thermostat. If the lower hose is about the same temp as the upper, you've got a flow problem.

The reservoir tank is in the circuit, but not really in the flow so it should be cooler.
If you can find a mechanic with an IR thermometer, the problem could be pinpointed.

You could also have a bum cap. Scum in the reservoir is a symptom of a head gasket leak. I tend to trust my gauges until they give me a reason not to. If it feels hot, it probably is.
Don't forget the fan clutch.
Ed

 

Sorry, bum feed here

 

I have a cheapie IR thermometer, a tiny little thing i got from Harbor Freight that you point & it gives you a temperature. What temps are normal at various points in the cooling system for a '91 240 that is fully warmed up?

Thanx,

ed

 

Most likely culprit is a bad thermostat. The giveaway is that it heats up more as soon as you get going. If the thermostat was open and the problem was the water pump, you would still get some flow due to fluid convection and some cooling (although limited) cooling while driving. And even if you're not sure, the thermostat is a good place to start since it's easy and cheap.

 

If you have an IR gun, the actual degree value is of little importance. What you want to do is scan the radiator and look for areas that vary appreciably in temp. Coolant enters at the top, cools from the airflow, becomes denser and sinks. It's moved along greatly by the water pump of course. Therefore, the hottest area should be near the top hose and drop evenly as you scan across and especially down. If you find a cool spot surrounded by warmer readings, that's indicative of blockage. Should you need to replace the radiator either 1. pay the dollars and get an o.e. Blackstone or Nissens radiator or 2. If you go the budget route, insist upon the three row radiator originally only used w/ turbo models. To test the fan clutch WITH THE ENGINE OFF reach in and try to spin the fan blade. It should have noticeable resistance to turning, but not difficult. It should turn smoothly, not jumpy nor should it free wheel. After checking the radiator, I'd buy a new thermostat and gasket and pull the housing. There's an amazing number of people who remove thermostats from B23x motors completely, not knowing that can actually make them run hotter. Since the car is new to you, these cheaper items are, IMHO, on the short list for replacement so I then know when they were last replaced. Ditto w/ the reservoir cap. If the head gasket is badly blown, often you can leave the reservoir cap off and rev the motor to 2500-3k when warmed up...coolant will vomit out of the reservoir like the Exorcist. Sometimes though, head gaskets are so imperceptable that the repair shop's chemical test won't pick it up in the coolant. So...test what you can and work from there.

 

Started it up & idled for about 1/2 hr, but didn't drive and the temp guage stayed pretty near the middle of its range. With an ambient air temp of about 40 d F, i got readings of about 160 on the top hose, 180 - 190 off the radiator near the top hose (driver side), about 170 - 180 towards the passenger side of the radiator, and the bottom hose was 150 - 160.

There was no pressure in the resevoir this time. Maybe it was slightly overfilled b4, a little above max.

Wondering if maybe it is OK, and it really is just an erratic guage.

I think i will replace or @ least test the thermostat, tho, as it is cheap & easy.

Thanx for all the helpful advice, always open to more.

ed