Series IIA Overheating with a new radiator

[tmckeon88]

I have a 1969 IIA 88 with a 2.25 petrol engine and it has always had very consistent heating/cooling behavior for the 20 years I've been driving it. The temperature gauge has always sat right at the top of the "N" of Normal, which is on the warm side, but that was always where it rested. I was experiencing some hot running last month which I attributed to an old, corroded radiator so I replaced it with the 4-core Proline unit from RN. It is still running a bit warm though, although not boiling over or leaking, because the level in the radiator remains full whenever I check it.

Two questions: 1) what should I check? and 2) where is the temperature sensor for the temp gauge? I don't see an obvious fitting anywhere- the little fixture beside the thermostat housing has nothing plugged into it.

Any suggestions would be helpful-
Tom

[TedW]

Hi Tom:

Why do you think it's running a little warm? Is the indicator in the same spot that it used to be in? My engines (original and replacement) have always run with the indicator in the spot you described.

You can always check your coolant temp with one of those snazzy infrared thermometers. Lacking that, you can always liberate your meat thermometer from the kitchen and check the coolant through the top cap opening when hot. You will probably discover that the engine isn't running as hot as you think it is.

Just my $0.02 - Wiser heads are certain to chime in.....

Ted

[tmckeon88]

Hi Ted-

The needle on the gauge is edging into the red, which it has never done in the past. Could there be an air pocket somewhere that's impeding the circulation? I let it run up to temp with the cap off so bubbles could work their way out. I'll try the thermometer- what should it read? I don't know what thermostat I have, should I be looking for something in the 170 range?

Tom

[o2batsea]

Jeezis, don't open the radiator cap when it's hot or you may end up in the burn unit! The coolant system operates under about 15 psi so that the coolant boils above 212F. If you open the cap you will be rapidly depressurizing the system along with releasing steam that wants to expand, what is it, like 300 times its liquid volume?
Anyway, assuming the radiator is new-ish, and the water pump impeller isn't eaten away to a nub and the passages aren't clogged with rust, and you have the proper thermostat, then you should suspect the gauge.

[SafeAirOne]

The other day, I noticed that my temp gauge is reading only slightly above the white "cold" arc on the gauge when the engine should be up to normal operating temperature. When I got home, I removed the wire from the temp sender and grabbed my ohm meter. With the ohm meter on the 0-200 ohm scale, I measured the resistance between the terminal on the temp sender and a ground on the engine.

The reading was 85 ohms, and using the trusty graph in THIS LINK HERE, I saw that the sender measured the coolant at 185 degrees Fahrenheit, so my gauge or voltage stabilizer is faulty. Nothing to worry about.

You can perform the same test--I believe that the gauges are the same on the IIAs and the IIIs, so the senders operate the same.

If the sender ohm reading is at or below your thermostat rating, then your gauge or, more likely, voltage stabilizer is off.

If the sender ohm reading indicates high coolant temp, then figure out a way to measure the ACTUAL coolant temp safely to see if it is, in fact, hot or whether the sender is bad.

[Manny]

You might need to burp your system. You may have air trapped somewhere.

[TedW]

Jeezis, don't open the radiator cap when it's hot or you may end up in the burn unit! The coolant system operates under about 15 psi so that the coolant boils above 212F. If you open the cap you will be rapidly depressurizing the system along with releasing steam that wants to expand, what is it, like 300 times its liquid volume?

FWIW I've never had this problem: I just put a cloth over the cap and turned slowly. That said, I agree with Manny that you may have some air in there somewhere.

Ted

[tmckeon88]

I'm going to try running it awhile with the cap off to see if more air comes through. I did that what I first filled it and it seemed contented enough, but it's still warm. I also replaced my heater core this spring with a new one and I'm hoping that is not somehow interfering with the process. I've removed my radiator cap when it's hot before and I use a rag and great care. But I intend to just run it from cold with the cap off this time.


Tom

[SafeAirOne]

Not sure where the temp sender is on your engine, but on the 2.5 its on the left rear of the cylinder head, amongst the head bolts by the bulkhead. I find that if I remove the sender and fill up the empty cooling system till it comes out the sender hole, then install the sender and top off the system, there's not a whole lot of air that gets trapped.

[tmckeon88]

I found the temp sender OK, it's under the thermostat housing. Since I last posted I have flushed and back flushed the cooling system from several different outlets. I also disconnected the heater core and flushed that- it was suggested that perhaps water did not flow through it in either direction, but it seems to fine. I tried reversing the hose connections on that, but the car still overheats after driving 5 miles or so. It creeps fairly slowly up into the red. I have a new thermostat on the way and I will try installing that. I will also try bypassing the heater altogether and seeing if the radiator works without that in the loop. That postpones the problem of a heater for a while, I guess. Any other ideas?

[SafeAirOne]

Did you say you put an ohmmeter on the temp sender "found it OK", or are you relating that you were trying to locate the temp sender on the engine and you've "found it OK"? After 20 years of driving it, I suspect you tested it and it checked OK.


Have you considered that the cooling system might be just fine, but some other problem exists that is causing the overheating?

Things such as:

Excessively lean fuel mixture

Cracked head

Defective lubrication system

Worn water pump (I know...that's part of the cooling system.)

Bad instrument voltage stabilizer

Poor instrument panel ground

Bad alternator regulator

Bad temp gauge

etc...

[tmckeon88]

I'm pretty sure it's not the gauge - After driving it a bit you can hear it wheezing and hissing as pressure tries to get out of the radiator. It has blown the expansion tank hose right off- I replaced that and clamped it more securely and now it will fill the expansion tank with overflow fluid pretty quickly. No change in lube issues that I can see- there's plenty of oil pressure. I bypassed the heater altogether and it still overheats. I talked to Rob at RN and he suggested removing the thermostat altogether and running without it. My new water pump is arriving tomorrow and I will install that and see what's what. (I tried turning the thermostat bolts today and thankfully they all moved!)

I am not sure about the leanness of the fuel mixture- I have a Weber carb which tends to run rich, in my experience, but I did do a tune up not long ago and leaned out the mixture screw a tiny bit. It starts, runs and idles well.

The investigation continues.

Tom

[tmckeon88]

Addendum: as far as the temp sender goes, I just meant that I located it without trouble. I haven't tested it, but it seems unmistakeable that the car is overheating.

[SafeAirOne]

Addendum: as far as the temp sender goes, I just meant that I located it without trouble. I haven't tested it, but it seems unmistakeable that the car is overheating.

Yeah, you're right.

Well, I think that presuming the fan belt is on and the mixture's not too lean, the thermostat and water pump are your last hopes to get this problem solved fairly painlessly.

[tmckeon88]

Well, I think I got it fixed- I replaced the water pump and thermostat, which required removing the radiator again, since I couldn't extract one of the long water pump bolts with the fan pulley in place. The fan and pulley also would not come off initially- just rusted onto the water pump shaft. Some PB Blaster and propane applied and it came apart. (Good thing, because those pulleys are NLA.) I replaced everything, including a new thermostat and got it all buttoned up and it seemed to run at its normal temp again. I also hooked the heater hoses up and it still seemed to be OK, so I don't have to face replacing the heater just yet. I suspect it was the thermostat because the water pump looked fine when I got it loose. I'll keep it as a spare.

Thanks to everyone who had suggestions for me.

Tom