kitttransam

Ever since I upgraded to afr 180 heads a few months ago my temp gauge seems to read high. About 10-15 degree difference. I checked the temp from the ECM on my laptop and it reads normal. Close to my infrared temp gun reading. I even changed out the temp switch on the passenger side and no change. I have tried making sure my cooling system is burped and I think I got all the air out. Scratching my head on this one.

GREGGPENN

Subscribed...

I observe the same on my 89 L98 with AFR 195s. I may have incorrectly assumed the temp difference was due to the LOCATION of the two sensors in the block/intake. That's because I was reminded of the water circulation path....which ends in the intake manifold, then enters the radiator at the top. That means [if anything] the dash should read lower than what the ECM "sees".

It's been several years, but I thought the ECM uses the sensor in the intake while the dash uses the one down by the dipstick. Could it be the other way around? If so, the readings would make more sense.

Are you sure it wasn't that way before the AFR heads? (I never noticed it until I did datalogging -- which was AFTER the new motor was built. So, I don't know if was the same before-hand.)

Edit: What did you point your gun at to get it's reading?

antfarmer2

Analog always lies ignore it.

kitttransam

Yeah before the head swap on a cool morning when driving to work my gauge would go down to 195. Now it'll go down to 205-207. I pointed my gun at the thermostat housing. Couldn't get a good reading pointing it at the head. The ECM does go by coolant sensor in the intake.

antfarmer2

Yes that is right try burping some more and water wetter.

WVZR-1

I doubt the suggested redo on burping and the added aggravation of the change over to "water wetter".

Confirm the resistance of the sender in the cylinder head and compare that to the FSM specs. There's a very wide +/- BUT maybe you could use it to just validate what you suspect. You don't need to rely on the dash gauge your only confirming cylinder head sender operation. If the the cylinder head sender is way out of the expected values then maybe you buy new sender and recheck.

ddahlgren

Analog gauge is commonly wrong. The other thing not discussed is the difference in cooling passages between heads. You only have one place to add metal for a stiffer deck, chambers and larger ports. That is the internal cooling passages.

kitttransam

I'm honestly thinking that it is the heads causing the temp difference. I put a new sensor in too and nothing changed. I actually emailed afr about this a few months ago and all they told me was probably air in the system. But I don't think that's the case.

antfarmer2

Yes it is very hard to pour a few ounce bottle in but if your up to the challenge two bottles dropped my temperature 8 degrees. and burping is just way to much work too. I have found if you jack it up it can get it out a bit easyer.

GREGGPENN

Do later years use a "needle"? I wouldn't call the early digital ("atari") dash analog.

kitttransam

If I was to burp again could do it in my driveway. It'll put my car at an incline.

GREGGPENN

I had water wetter before my recent coolant change. I didn't re-add it because I didn't think it helped (back when I put it in). OTOH, I feel like my temps are a bit higher than before. So maybe it does give a small bump.

kitttransam

I don't think I need water wetter. Have a Dewitt's radiator and the Dewitt's spal fan.

kitttransam

I just had a thought. When I did my head upgrade I bought an extra intake that I ported out. This intake has the spot for the cold start switch which I blocked off. Wonder if it's possible to relocate the temp sensor for the gauges to the intake. Is it the same threads?

antfarmer2

My 94 has the digital and analog the latter lies.

Ratboy

A few years back a head gasket went on my 89. I had installed the afr heads a couple years previous to that and coolant temps were normal until that gasket went. After the head gasket job I gained about 5-10 degrees as you describe. AFR said the same thing about burping the system, but it never came back down. Never got too hot either, just not as cool as it used to be. I suspected that I may have swapped the intake manifold gaskets - One end only has a 1/4" hole while the other is slightly larger than the port. Swapping them would have affected the circulation IMHO. I never went back in to check since I also had the Lingenfelter/Accel intake which was a major pain to r&r. There seemed to be a lot of conjecture about the gaskets since some of them have full size ports on both ends depending on the application. My car also had the "steam port" that routes coolant from the back of the manifold to the heater hose, which I think was a partial year or Corvette only design. It seems Chevy employed different strategies over the years for coolant balance. If I still had the car I would pull it apart just to figure it out, but at the time it was winter in NY and with no garage, I wasn't up for it.

GREGGPENN

That's a good point. The restricted intake gaskets "held" coolant in the back of the intake for a longer period of time. When I swapped to AFRs, I'm pretty sure I used gaskets with the rear ports open. Would that raise temps for the dash sending unit?

Seems like the removal of any restriction would lower temps....meaning mine should have dropped with the rear ports opened AND HV water pump AND bigger radiatior. Kinda goes to the theory of coolant speed...

Normally, you read that any increase in coolant speed improves cooling. OTOH, I've read a post here/there where the ADDITION of a restricting piece lowered temps. (Take, for example, the L98 rear intake passage.)

kitttransam

I just realized something since intake gaskets were brought up. I believe my intake gaskets are fully open in the rear. Wonder if that could cause a problem. I bought the gaskets afr recommended.

kitttransam

Yeah I have to use 1256 felpro intake gaskets. I looked on summit and the only ones with the rear blocked off are stock style and ports. Is there a way to block the rear ports while using the 1256 gaskets?

GREGGPENN

Here's a better explanation...

In reading through older threads (where I mentioned this temp issue), someone pointed out that water makes it way from the water pump intake to the return via many routes. Water that travels through the heads (and to the rear of the motor) gets hotter. In short, the cts used to pass info to the dash might just have hotter fluid. That's because SOME water passes on a straighter path [up to the thermostat housing] -- which means cooler water is mixing with the water as it enters the return hose.

When the restrictive intake gasket is removed, more water passes through a longer path (through the heads) resulting in an increase of water temp near the dash sensor.

When you measured temp at the housing, the fact it matches what the computer "sees" is expected. The trick would be to measure temps near the dash sensor to make sure it's really reporting the correct number.

I suspect the temperature really IS hotter with the new style intake gasket...especially since you noticed lower temps BEFORE the head/intake swap.

Note: This is an unproven theory. I'm proposing it based on additional feedback of how coolant flows.